SeaData

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ChartPosmanual position — not a vessel position

SeaData

Time (UTC)	CMEMS NWS	Met Office NWS	IBI	MED	EOT20	FES2022	DTU23	TidesAtlas
Data appears once the chart has loaded.

🌊 DMI WAM - 1.1km

Wave total

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Wind wave

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Swell

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Wave period

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Wave direction

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🌊 CMEMS Wave - 1.5km

Wave total

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Wind wave

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Swell

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Wave period

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Wave direction

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Swell dir.

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🌊 Met Office NWS - 1.5km

Wave total

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Wind wave

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Swell

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Peak period

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Mean period

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Wave direction

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Swell dir.

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🌊 MFWAM - 2.5km

Wave total

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Wind wave

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Swell

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Wave period

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Wave direction

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Swell dir.

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Max wave

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Freak index

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🌊 IBI Wave - 3km

Wave total

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Wind wave

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Swell

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Peak period

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Mean period

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Wave direction

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Swell dir.

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🌊 WW3 4km - MET Norway

Wave height

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Wave period

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Wave direction

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🌊 DWD EWAM - 5.5km

Wave total

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Wind wave

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Swell

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Peak period

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Energy period

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Wave direction

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Swell dir.

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🌊 Med Wave - 4.2km

Wave height

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Wave period

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Wave direction

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🌊 WW3 MEDITA - 11km

Wave height

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Peak period

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Mean period

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Wave direction

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🌊 ECMWF IFS

Wave height

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Mean period

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Direction

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🌊 CWA lokaal - Taiwan

Wave height

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Wave period

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Wave direction

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🌊 CMEMS Asia - 9km

Wave height

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Peak period

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Wave direction

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🌊 MET Office ASIA

Wave height

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Mean period

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Wave direction

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🌊 CMEMS Japan - 9km

Wave height

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Peak period

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Wave direction

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🌊 JMA Global Wave

Wave height

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Peak period

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Second period

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Wave direction

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Time (UTC)	DMI WAM	CMEMS Wave	Met Office NWS	MFWAM	IBI Wave	WW3 4km	DWD EWAM	Med Wave	WW3 MEDITA	ECMWF IFS	CWA lokaal	CMEMS Asia	MET Office ASIA	CMEMS Japan	JMA Global Wave
Wave height (m) per source; data appears once compute is active.

Daily progress report

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Time (UTC)	Wave total m	Max wave m	Wind wave m	Swell m	Period s	Direction °
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One source: the model that fits this position best. Empty rows before the model run are shown as —, not as zero.

SeaWave

Waiting for wave data…

Models, ranked

for this position

Above the dashed line: the top 3 that make the readouts. Click a model to show its components.

Checked against satellites

Hs · all models

Components

m · s · direction from

TotalWind seaSwellPeak period (s, right)

Time (UTC)	Tidal m/s	Tidal dir	Total m/s	Total dir	Resid. m/s	Resid. dir
Data appears once the compute layer delivers currents.

— CWA lokaal— WRF 3km— ECMWF IFS— GFS— ICON global— ICON-D2— ICON-EU— JMA GSM— HARMONIE— HARMONIE DINI— MEPS— UKV— AROME- - HDG (heading)- - COG (course over ground)wind arrows point FROM, ship arrows point TO

Shipping forecast

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Loading…

CWA lokaal

Wind—

Gusts—

Direction—

Pressure—

Temperature—

Precipitation—

Cloud cover—

WRF 3km

Wind—

Gusts—

Direction—

Pressure—

Temperature—

Precipitation—

Cloud cover—

ECMWF IFS

Wind—

Gusts—

Direction—

Pressure—

Temperature—

Precipitation—

Cloud cover—

GFS

Wind—

Gusts—

Direction—

Pressure—

Temperature—

Precipitation—

Cloud cover—

ICON global

Wind—

Gusts—

Direction—

Pressure—

Temperature—

Precipitation—

Cloud cover—

ICON-D2

Wind—

Gusts—

Direction—

Pressure—

Temperature—

Precipitation—

Cloud cover—

ICON-EU

Wind—

Gusts—

Direction—

Pressure—

Temperature—

Precipitation—

Cloud cover—

JMA GSM

Wind—

Gusts—

Direction—

Pressure—

Temperature—

Precipitation—

Cloud cover—

HARMONIE

Wind—

Gusts—

Direction—

Pressure—

Temperature—

Precipitation—

Cloud cover—

HARMONIE DINI

Wind—

Gusts—

Direction—

Pressure—

Temperature—

Precipitation—

Cloud cover—

MEPS

Wind—

Gusts—

Direction—

Pressure—

Temperature—

Precipitation—

Cloud cover—

UKV

Wind—

Gusts—

Direction—

Pressure—

Temperature—

Precipitation—

Cloud cover—

AROME

Wind—

Gusts—

Direction—

Pressure—

Temperature—

Precipitation—

Cloud cover—

Ensemble average (all models, now)

Wind—

Gusts—

Pressure—

Precipitation—

Temperature—

Direction—

Best-fitting model

Wind—

Gusts—

Pressure—

Precipitation—

Temperature—

Direction—

Wind (m/s)

Gusts (m/s)

Pressure (hPa)

Precipitation (mm)

Temperature (°C)

Wind direction (°)

Day	Wind	Gust	Dir	Temp	Rain
7-day forecast appears once compute is active.

Time (UTC)	Wind	Bft	Gust	Dir
Three-hourly values appear once compute is active.

Loading models…

Time (UTC)	Wind m/s	Bft	Gust	Dir	Temp	Rain	Press	Cloud
Data appears once compute is active.

Shipping forecast issued by KNMI for the North Sea districts, the Dutch continental shelf and the coastal districts. Written by a meteorologist — not model output.

Loading…

Tropical cyclone monitoring for the waters around Taiwan, issued by the Central Weather Administration (CWA). Positions, intensities and forecast per bulletin.

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SeaWind

Waiting for wind data…

Models, ranked

wind · now

Above the dashed line: the top 3 that make the readouts. Click a model to follow it in Charts.

Wind rose

Day	Rise	Set	Length	Moon	Illum.
7-day overview appears once compute is active.

Port	Country	Dist.	Max LOA	Depth	Size
Loading ports…

Port	Country	Distance	Source	Now	Next HW	Next LW
Loading ports…

Demo — the Demo vessel at the demo position in the North Sea, with today’s forecast. Change any field and press Calculate; with an account you work with your own vessels, drawings and position, and can save them.

Vessel

Positionfollows the mapMoment

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No calculation yetPick a moment and press Calculate. Wave, wind and current are taken from the same sources the SeaWave, SeaWind and SeaCurrent tabs show for this position.

workable < 0.8marginal 0.8 – 1.0not workable > 1.0roll resonancering = the limit; the wedge reaches it at ratio 1.0

What it calculated with

Moment (UTC)	—
Wave source	—
Hs / Tp / direction	—
Wind sea / swell	—
Wind	—
Current	—
Calculation point	—
Wind area	—
Sea state shape	—
Station keeping	—

Waves: SWAN at your position comes first. When SWAN is not used, Wave source says why and the model that won the ranking for this position takes over. The name in brackets is that model — the same ranking the other tabs use.

On the best heading

Motions	—
Limited by	—

Significant amplitudes unless you picked the 3-hour maximum on the Limits tab.

Confidence

—vessel data 50 · environment 30 · validity of the theory 20

Limits of the theory

Heave and pitch: linear theory, indicative above Hs of about Lpp/20. Roll: damping linearised for this sea state (ITTC 7.5-02-07-04.5).
No parametric roll. Green water and slamming as probabilities per wave (relative motion at the bow, Ochi 1964), without the bow wave pile-up.
Roll damping is the largest uncertainty: a factor 2 in damping is a factor 2 in roll amplitude at resonance.
Station keeping is static (mean forces): no dynamic DP control, no thruster interaction or ventilation.
Following seas: encounter frequency can approach zero and is clipped at 0.05 rad/s.

Computed in —. Roll near resonance is on the conservative side: the closed-form model over-predicts it, which for a workability call errs towards "do not work" rather than the other way round.

Positionfollows the mapHorizon—

No calculation yetPress Calculate. Wave, wind and current come from the same sources as the SeaWave, SeaWind and SeaCurrent tabs; every value is the average of the best 3 models for this position, visibility the lowest of them.

Timeline per activity

One block per hour (UTC). An hour counts only if every assessed limit is met AND it falls inside a window at least as long as the activity’s minimum. Hover over an hour for the values; click an activity to see its weather below.

workableworkable, near the limit (within the margin)just over the limit (within the margin, not workable)weather OK, window shorter than the minimumnot workable (limit exceeded)window runs past the horizon, length unknownno model datalower block: chance in % that Hs and wind stay within the limits (ensembles) — brighter is more likely

Windows

The next window per activity that meets its minimum length. Workable counts the hours within the horizon.

Activity	Now	Min. window	Next workable window	Length	Most limited by	Workable	Chance now

Weather against the limits

Line = average of the models (visibility: the lowest model), band = lowest to highest model, dashed = the limit of this activity. Hours near the limit are shaded light orange, just over it dark orange, further over it red. Visibility is drawn up to 12 km. Same time axis as the timeline.

Working limit for safe 24h vessel operations on site

One row per activity. An hour is workable when Hs, wind and current stay at or below the limit and visibility at or above it. Min. window: a calm spell between two bad-weather periods that is shorter than this does not count as workable. Visibility can be set up to 12000 m.

Near-limit margin %Hours within this percentage of a limit turn orange: light when just inside (still workable), dark when just over. 0 = off.

Activity	Significant wave height Hs (m)	Max. wind speed @10 m, 1 h avg (m/s)	Current Uc (m/s)	Visibility (m)	Min. window (h)

Demo: example contract values. Sign in to set the limits of your own vessel.

Fromwaiting for the AIS position…Set speedkn through waterLimitsOff tracknmReverse route

Transit follows a live AIS position and speed. The demo screen has neither, so this tab only shows how it is laid out. Sign in with a vessel of your own to plan a route.

No route yetPress Waypoints on the map, click the track you intend to sail, and press Calculate. Wave, wind and current come from the same sources as the SeaWave, SeaWind and SeaCurrent tabs; the limits come from Contract.

Route and waypoints

Waypoint 0 is the vessel and moves with it — you never set that one.

Route options

The same forecast and the same limits over every track, each at the speed the vessel is making now. Miles are not the whole story: a longer route that stays out of the weather can still be the better one. Click a row to select it.

Route	Passage per hour	Distance	ETA	Over the limit	Max Hs	Verdict

Passage against the Contract limits — set speed vs speed now

One block per hour of the passage, on the same clock. The upper row is the plan, the lower row is the speed the vessel is really making. Same route, same forecast — the speed decides when you are where, and that decides the weather you get. Hover a block for the values.

within the limitswithin, but inside the marginjust over a limitover the limit — slow down, alter course or stopno model data

Weather along the route

Both graphs run over the same route (nautical miles from the vessel, bottom axis) but each reads the forecast on its own clock (top axis). Line = average of the models, band = lowest to highest, dashed grey = the other speed, dashed red = the limit of this activity. Between the sample points the forecast is interpolated; the dots on the axis are the points that were actually fetched.

Speed, tide and ETA

What the set speed and the measured speed give over the ground along this route, with the tidal stream of that hour on top. That is why neither line is flat and why the ETA moves. The pale block is the ETA spread from the last two hours of measured speed.

What this means

Demo — example limits. Sign in to report against your own vessel and contract.

Vessel—TechniquePositionfollows the map

Pick a technique and press Create reportThe report covers the running day and the day after, from 00:00 UTC. It shows what is over the limits and by how much, how long the adverse weather lasts, when work can resume, what the models say and how far they disagree. The limits are the ones saved for this vessel — the report only reads them.

Demo — uploading needs an account. Sign in to read your own supplier forecasts.

Dummy dataThis screen shows an invented supplier forecast so you can see what it does. Nothing here was uploaded and nothing is real. With an account you upload the PDF your own supplier sends, check what we read from it, and release it for the report.

Vessel—Positionfollows the map

Upload or e-mail the forecast your supplier sendsDTN, StormGeo and Infoplaza are read from the text layer of the PDF: the forecast table, the units and the time zone are taken from the document itself and converted to metres, m/s and UTC. You see here exactly what we read before it is used anywhere.A forecast is only data for this vessel if the position in the document lies within 50 km of it. Between 50 and 100 km it is plotted here with a warning and its distance, but it cannot be released and is used nowhere else in SeaData. Further than 100 km, or no position, and it is read (DPR and PDF work) but not plotted.Nothing is used until you press Use in SeaData. Until then it stays on this screen and appears nowhere else.

History — with an account, SeaData stores the conditions around your vessel every hour, so you can look back at any moment or period.

Dummy dataThere is no vessel sending here. What you see below is an invented feed, so you can see what this tab does. With an account you point SeaData.exe on board at your API key and this fills with what your own vessel sends — position, heading, roll, pitch and heave, wind, pressure and temperature, every six seconds.

Feedwaiting for the first burst…EndpointPOST /api/schip/nmea · https, port 443—
waitingAPI key & SeaData.exe

What this feed is used for today: position. That is what goes to the map, the vessel selector and Transit, on top of shore AIS. Heading, motion and weather arrive as well and are kept for six hours so they can be looked at — they are not used in any calculation yet.

Position and heading

What the server reads from your bursts and puts on the map, on top of shore AIS.

Value	Now	From	Age

Motion — measured, not modelled

From $PSDMO: the largest excursion per axis over the window, sign kept — not a snapshot. Roll + is port up, pitch + is bow up, heave + is up, whatever sensor is fitted. Careful with the limits in the Limits tab: those are significant amplitudes and this is a maximum, which typically runs one and a half to two times higher. They are not the same measure.

Weather on board

Wind from the two MWV sentences, pressure and temperature from MDA.

Value	On board	From	Age

Last 6 hours

Six hours is the whole memory — older than that falls off, and nothing goes into the database. One point per minute: for roll, pitch and heave the largest excursion in that minute, for wind and pressure the average.

Last burst received

The raw lines, exactly as they came in.

Refused bursts

A burst with a wrong key (401) belongs to no vessel and cannot be shown here — it is refused before we know which ship it is.

Time	Code	Why	Lines

You place things in the top view and the side view — two orthographic windows at the same scale, one above the other, where a click resolves to exactly one number — on the outline of the standard hull, or on your own drawing once you upload one below. Positions go the way a general arrangement gives them: y along the ship from the stern, x across it from the centreline (+ starboard) and z from the deck (+ up), all from the zero point 0,0,0 at stern, centreline and deck.

Your drawing

Top view (DXF)Side view (DXF)Name

Top, side or both, max 5 MB each. Nothing is built from it: the lines are only placed in ship coordinates.

Top view

A click places

Fill in the vessel type, Lpp and beam in step 1 under Vessel › Config and the hull appears here.

A click moves the selected unit across and along; with nothing selected it adds a unit. The dashed line is the waterline at your draught.

Side view

A click places

Fill in the vessel type, Lpp and beam in step 1 under Vessel › Config and the hull appears here.

Seen from starboard. A click sets the height (and the position along) of the selected unit, the working point or the centre of gravity. The shaded band is below the waterline.

Tunnelacross the ship onlyAzimuthany directionAzimuth, reversedany direction, less thrustMain propelleralong the ship onlyVoith Schneidercycloidal, any directionRudder in DPacross only, at the rudder stockGill jetany directionOther pointdraft marks and the like — drawn, never computedZero point 0,0,0stern, centreline, deck — everything is measured from hereCentre of gravityevery lever arm starts hereWorking pointthe calculation point for the motions — the CoG when emptyWaterlineat the draught you enteredSecond waterlinethe other loading condition, reference onlyRoll axistransverse acceleration measured from here

Positions, all measured from 0,0,0

The zero point is the stern, on the centreline, at deck height — the quadrant mark on the drawing. z is positive up, so anything inside the hull is negative: a tunnel 10 m below the deck is −10. The module converts to lever arms about the centre of gravity itself, and the table below gives every position in both frames.

Centre of gravity

CoG ymfrom the stern; Lpp/2 if empty

what is this?

Longitudinal position of the centre of gravity, measured from the stern - the LCG from the stability booklet, for this loading condition. Leave it empty and it sits at half the length, which is a fair guess for most ships but still a guess. It scales EVERY lever arm in the calculation: each thruster arm, the yaw moment that wind and current put on the hull, and the pitch and roll arms of the working point. A ship trimmed by the stern can easily have its CoG several metres aft of amidships, and on a 168 m hull that is thousands of kNm of yaw that would otherwise sit nowhere.

CoG xmfrom the centreline, + starboard

what is this?

Transverse position of the centre of gravity from the centreline, positive to starboard. Zero for a ship sitting upright, and that is the normal case. Fill it in for a fixed list or a badly one-sided load: it shifts the yaw arm of every unit and of the wind force.

CoG zmfrom the deck, + up (KG - D)

what is this?

Height of the centre of gravity, in the same frame as every other point on this tab: from the deck, positive up - so the KG from the stability booklet minus the moulded depth D, and nearly always negative. It is drawn in the side view. When it is filled in, the ship rolls about its centre of gravity: the roll axis sits at KG, and every transverse acceleration is measured from there. Left empty, the roll axis follows from the depth and the draught (DNV Sec.4 B403).

Other loading condition

CoG y, other conditionmreference only

what is this?

Longitudinal position of the centre of gravity in that other condition, from the stern. Drawn as a second, dimmer node. Reference only - every lever arm in the calculation uses the CoG of the condition you are working in. A hopper that trims by the stern when full and sits level when empty moves its CoG several metres, and seeing both tells you which thrusters lose their arm.

CoG x, other conditionmreference only, + starboard

what is this?

Transverse position of the centre of gravity in the other condition. Normally zero; fill it in for a fixed list. Reference only.

CoG z, other conditionmreference only, from the deck

what is this?

Height of the centre of gravity in the other condition, from the deck, positive up (KG - D). Drawn in the side view. Reference only.

Working point

This is the calculation point: heave, vertical and transverse acceleration on the Waves card are worked out here. It does not have to be a place where work is done. Leave it empty and the calculation uses the centre of gravity. Wind and Current always work about the centre of gravity.

Working point

namexyz

the CALCULATION POINT - empty = the centre of gravity

what is this?

The CALCULATION POINT of the Waves card: heave, vertical acceleration and transverse acceleration are worked out AT THIS POINT and compared with your limits there. It does not have to be a place where anyone works; pick the point whose motion matters - the crane tip, the moonpool, the survey sensor, the bridge - and give it a name, so the answer says which point it is about. Position in the same three numbers as everything else on this tab: x across from the centreline, y along from the stern, z from the deck with positive up. The vertical motion there is heave plus the pitch and roll lever arms, so a point far forward can move several times as much as the centre of gravity does, and the TRANSVERSE acceleration needs the height. LEAVE IT EMPTY AND THE CALCULATION POINT IS THE CENTRE OF GRAVITY: only heave counts there, which is the friendliest answer the ship can give. Roll, pitch and Hs are the same everywhere on the ship, and the Wind and Current cards do not use this point at all - station keeping is always worked out about the centre of gravity.

Loading — the two draft marks

0 % is empty (the lower mark), 100 % is down to the upper mark. The percentage sets the waterline, and with it the draught the whole calculation uses — it replaces the draught from step 1.

0 % - empty, LOWER draft markmz from the deck, so the more negative of the two

what is this?

The waterline with the ship EMPTY: the LOWER draft mark, the shallowest draught she floats at. Given from the zero point of this tab - z from the deck, positive up - so it is negative, and it is the more negative of the two marks because an empty ship floats high and her waterline sits far below the deck. On a 168 m hopper with 12.15 m of loaded draught and a 13.97 m depth, empty might be -7.8.

100 % - loaded, UPPER draft markmz from the deck, so the less negative of the two

what is this?

The waterline with the ship down to her UPPER draft mark: fully loaded, the deepest draught she is marked for. Same frame, so also negative, but CLOSER TO ZERO than the empty mark - a loaded ship sits deep and her waterline comes up near the deck. On that same hopper, -1.82 with 1.82 m of freeboard left. Together the two marks define the whole loading range and the percentage below says where on it you are.

Loaded% of the draft mark0 = empty, 100 = down to the mark

what is this?

Where between the two waterlines the ship is right now, as a percentage: 0 is empty, 100 is down to the draft mark. The module interpolates the waterline between the two, and THAT is the draught the whole calculation uses - it replaces the draught from step 1, and the screen says which figure it ended up with. Everything that hangs off the draught follows: the freeboard and therefore the wind area, the height of the roll axis, and the submergence of every thruster. A hopper at 40 % is a genuinely different ship to compute with than the same hopper at 100 %.

Thrusters

WITHOUT AT LEAST ONE UNIT WITH A POWER FIGURE the Wind and Current plots stay empty - they are station keeping only.

what is this?

One row per unit: type, shaft kW, and the position on the drawing - x across from the centreline, y along from the stern, and z from the DECK with positive up, so a unit inside the hull has a negative z. The height does not enter the horizontal force balance (that is three degrees of freedom and none of them vertical), but it tells you how deep the unit sits: submergence is the draught minus z, and a unit close to the surface ventilates. A tunnel thruster that sucks air loses more than half its thrust while it does so. Power is the SHAFT rating, not the generator rating. Thrust per kW comes from IMCA M 140 section 2: tunnel 0.145 kN/kW, azimuth ahead and main propeller 0.171, azimuth with reversed pitch and gill jet 0.105. The position decides the lever arm and therefore how much heading the ship can hold - two main propellers either side of the centreline hold a heading in push/pull, one on the centreline holds none at all, and until the transverse position could be entered the model could not tell those two apart. A row without a power figure is ignored rather than counted as zero.

Other points

anything you want to see on the drawing

what is this?

Points of your own: draft marks, the A-frame, a hatch corner, the moonpool, a sounding pipe - a name and the same three numbers as everything else on this tab (x across, y along, z from the deck with positive up). They are drawn in all three views and listed in the table with their position in both frames, and they take part in NO calculation whatsoever. That is the point of them: they are there so you can see how the things that DO count sit in relation to the rest of the ship.

What this layout can do

No weather is involved: this is what the geometry and the installed power give on their own, so you can see what moving a unit buys before fetching a forecast. Thrust per kW is from IMCA M 140 section 2. The totals are an upper bound per axis — an azimuth unit is counted in full in all three, and in reality it cannot do all three at once.

Surge, fore and aft—kN after the worst case failure

Sway, athwartships—kN after the worst case failure

Yaw—kNm after the worst case failure

Preferred vesselOpens first after a refresh. One vessel at a time.Saving uses the profile name (step 1) and the loading condition (step 2). Same pair = same profile.

Step 1 · Required

Without these five nothing can be calculated. Everything else may stay empty - then the rule of thumb for the vessel type is used.

Profile name

what is this?

Your own name for this vessel. Together with the loading condition in step 2 it identifies a saved profile, so the same ship loaded and in ballast live side by side as two profiles.

Vessel typesets every rule of thumb

what is this?

Picks the row in the vessel type table that fills in everything you leave empty: hull ratios, block coefficient, GM, roll period, radii of gyration and roll damping. Choose the closest HULL FORM, not the closest job title - the table is about shape. Hull forms the theory does not cover are listed at the bottom of this tab with the reason.

Lppmlength between perpendiculars

what is this?

Length between perpendiculars - stem at the summer waterline to the rudder stock - and NOT the length overall a brochure publishes, which is typically 3 to 5 percent longer. It sets the pitch response, the lateral wind and current areas, and the scale at which a wave counts as long or short for this ship: above Hs of about Lpp/20 the linear theory leaves its range.

Beam Bmmoulded, at the waterline

what is this?

Moulded beam at the waterline. With GM it sets the roll period (T = 2 k B / sqrt(GM)), so it drives the whole roll picture, and it is the reference width for the current force along the ship.

Draught Tmmean, in the working condition

what is this?

Mean moulded draught in the condition you are going to work in - not the maximum on the load line. It sets the underwater lateral area for the current force and, with the beam, the sectional shape the model uses for the wave damping.

Working speedkn0 = stationary / DP. Above 0 the station keeping numbers still appear, with a caveat.

what is this?

The speed you actually WORK at, not the transit speed. It shifts the encounter frequency - the ship meets head seas sooner and following seas later - and that moves the whole polar. A capability plot is defined at zero speed; above zero the station keeping figures are still shown, but read them as the load on that heading and not as a capability number.

Step 2 · Stability booklet

Six values from the stability booklet. GM weighs heaviest: it drives the roll period and therefore the whole polar.

Loading conditionseveral per profile

what is this?

The condition the figures below belong to: loaded, ballast, hopper full, hopper empty. Draught, GM and roll period all change with it, so a full and an empty ship are two genuinely different ships to compute with. Saving uses profile name plus this field, so both can be kept.

Displacementtreplaces the calculated value

what is this?

Displacement in tonnes for this loading condition, from the stability booklet or the loading computer. Left empty it is computed as Cb x Lpp x B x T x rho. It is the mass in the roll equation and it scales the wave drift force.

Block coefficient Cb0.5 tug ... 0.85 dredger

what is this?

The displaced volume divided by Lpp x B x T: how box-like the hull is. Roughly 0.50 for a tug, 0.60-0.70 for a survey or construction vessel, 0.80-0.88 for a hopper dredger or a loaded tanker. The model replaces the ship by a box of beam B x Cb so that the mass comes out right, which makes Cb the way the real hull enters the calculation. Left empty: the midpoint of the range for the vessel type.

GM (this loading)mheaviest weighing field

what is this?

Transverse metacentric height GMt for this loading condition, corrected for free surfaces, from the stability booklet. This is the most valuable field on the tab. The roll period goes with 1/sqrt(GM), and the roll period decides whether the sea puts this ship on resonance: a stiff ship (large GM) rolls short and hard, a tender ship rolls slow and far. Fill this in and the roll period is COMPUTED from it instead of read from the table.

Natural roll periodsone stopwatch measurement

what is this?

The natural roll period in seconds. Get the ship rolling alongside or in calm water, time ten full swings with a stopwatch and divide by ten. Two minutes of work, and it beats every table in this module: GM, radius of gyration and added mass all come together in this one number. If the polar shows a resonance mark, this is the field that decides whether that warning is real.

Moulded depth Dmbaseline to the main deck

what is this?

Moulded depth: the height from the BASELINE (top of keel) to the main deck at the side, amidships. Together with the draught it gives the freeboard, so filling in either one gives you both - and it fixes the height of the roll axis, which DNV puts at the smaller of D/4 + T/2 and D/2 above the baseline. That axis is what the transverse acceleration is measured from, so this field is what makes the height of a working point mean anything. Left empty it is the draught plus the estimated freeboard.

Freeboardmgreen water limit + wind area

what is this?

Freeboard amidships: deck edge above the waterline in this condition. It sets the HEIGHT of the wind area and therefore the wind force in the station keeping chain. Worth entering: measured across a real fleet the rule of thumb for dredgers turned out four times too high - a loaded hopper dredger has about 0.15 x draught of freeboard, not 0.60 - which is 43 percent of the lateral wind area.

Freeboard at the bowmgreen water at the bow

what is this?

Height of the deck edge (or the bulwark top) at the stem above the waterline in this condition. Green water is counted when the RELATIVE motion at the bow - the ship against the wave - is larger than this. Left empty it is the freeboard amidships plus the standard sheer of the Load Line Convention at the forward perpendicular, 50 x (Lpp/3 + 10) mm: 1.3 m on a 50 m ship.

Step 3 · Extended - motions

Everything that sharpens chain A. The roll damping is the weakest spot of the theory: a factor 2 in damping is a factor 2 in roll. The working point moved to Vessel › 2D, where you can put it on the drawing instead of working out its distance from the centre of gravity yourself.

kxxmroll radius of gyration, in metres

what is this?

ROLL RADIUS OF GYRATION. The distance at which the entire mass of the ship could be concentrated and still resist rolling in the same way: Ixx = displacement x kxx^2. Weight far out to the sides - deck cargo at the rails, full wing tanks - makes it large and the roll slow; weight low and on the centreline makes it small and the roll quick. It is typically 0.33 to 0.52 times the BEAM, 0.42 on average across the class societies (Grin, IMDC 2024); this module estimates 0.35-0.40 x B per vessel type. ENTER IT IN METRES, not as a fraction of the beam. It comes from the inertia calculation in the stability booklet; if you do not have it, a stopwatch reading of the roll period is worth more than a guess here.

kyympitch radius of gyration, in metres

what is this?

PITCH RADIUS OF GYRATION - the same idea as kxx but about the transverse axis: Iyy = displacement x kyy^2. It is set by weight far forward and far aft, which is why a ship loaded at the ends pitches slowly. The usual rule is 0.24 to 0.26 times Lpp and this module uses 0.25 x Lpp. No published table of typical values per ship type was found, so this one stays a rule of thumb whatever you do. Enter it in metres.

Roll damping% crit

from a roll decay test

Two successive roll amplitudes to the same side, in degrees:

or use the tick boxes

what is this?

Viscous roll damping as a percentage of critical damping: what bilge keels, hull friction, eddies and appendages take out of the rolling, ON TOP of the wave damping the model computes itself. This is the largest uncertainty in the whole module - at resonance a factor 2 in damping is a factor 2 in roll angle. The default is 20 percent, the value the source paper matches to model tests. The tick boxes build a figure instead (4 percent bare hull, 7 with bilge keels, +4 anti-roll tank, +8 fin stabilisers) and those numbers are rules of thumb without a source. If a roll decay test has ever been done on this ship, its result is the most valuable number you can type anywhere on this tab: open "from a roll decay test", enter two successive amplitudes to the same side, and the logarithmic decrement delta = ln(a1/a2) gives zeta = delta / sqrt(4 pi^2 + delta^2). That is the TOTAL damping of the ship at its natural roll period; for a normal hull the wave damping there is small, so it is a fair value for this field - if anything on the high side.

Bilge keels

what is this?

Bilge keels roughly double the viscous roll damping of a bare hull. Nearly every working vessel has them - tick it unless you know otherwise.

Anti-roll tank

what is this?

A passive or active anti-roll tank, worth about +4 percent of critical damping here. In reality a passive tank only works near its own tuning frequency, so treat this as the optimistic end.

Fin stabilisers

what is this?

Active fins, worth about +8 percent of critical damping here. Fins need speed to make lift: at DP or at a few knots they do almost nothing, so do not tick them for stationary work.

Awp or Cwpm2 / -heave stiffness

what is this?

Waterplane area in m2, or the waterplane coefficient Cwp as a number below 1 - the field takes either and tells them apart by size. It is the heave stiffness (rho x g x Awp): more waterplane means a stiffer and shorter heave. Left empty it is Cwp x Lpp x B with Cwp = 2/3 Cb + 1/3 (Barrass).

Step 4 · Station keeping (DP)

Only meaningful at working speed 0. Without these fields chain B is skipped and the polar shows motions only. The thrusters themselves are on Vessel › 2D: where a unit sits is what decides how much heading it can hold, and that is easier to place on a drawing than to type as a lever arm.

DP classnone / DP1 / DP2 / DP3

what is this?

The DP notation of the vessel. It is used for exactly one thing: how much thrust is assumed to survive the worst case single failure - DP1 keeps 100 percent, DP2 and DP3 keep 50. That 50 is the IMCA M 140 default (loss of one engine room and with it half the thrusters), not a rule; your own figure goes in the last field of this step.

Wind area frontalm2B x (freeboard + 6) if empty

what is this?

Projected area of everything above water seen from DEAD AHEAD, in m2: hull side, deckhouse, containers, crane pedestals, A-frame. It sets the wind force along the ship. A figure here wins over your drawing; left empty it comes from the drawing, or is estimated as B x (freeboard + 6 m).

Wind area lateralm2Lpp x (freeboard + 4) if empty

what is this?

The same projected area seen from ABEAM, in m2. It is typically three to five times the frontal area, which is exactly why beam-on wind is the hard direction for station keeping. A figure here wins over your drawing; left empty it comes from the drawing, or is estimated as Lpp x (freeboard + 4 m).

Wind area centroid heightmabove waterline

what is this?

Height of the centre of the lateral wind area above the waterline, in metres. It is the lever arm of the wind HEEL: the side wind times (this height + half the draught) over the righting moment gives a steady heel that is added to the roll on the Waves card (IMO weather criterion). Left empty it comes from your side view, or is estimated as (freeboard + 4) / 2. For a ship with a large deckhouse it is roughly half the height of that block above the water.

Underwater lateral aream2Lpp x T if empty

what is this?

Projected underwater area seen from abeam, in m2: about Lpp x T, plus skegs, a keel, a dredging ladder or a moonpool trunk. It sets the current force abeam and the current yaw moment, which at one knot are often the same order of magnitude as a fresh breeze. Left empty Lpp x T is used.

Worst case failure% thrust lost50 if empty; IMCA M 140 s3

what is this?

How much of the installed thrust the worst single failure takes away, as a percentage. IMCA M 140 section 3 assumes the loss of one engine room or half the main switchboard, and with it half the thrusters - hence 50 as the default. Your real figure is in the vessel FMEA and can be very different when the thrusters are split three ways. It scales the Wind and Current plots directly.

Not offered, and deliberately so: Jack-up installation vessel - stands on legs while working, Jack-up platform - same reason, Backhoe dredger - works on spuds, not floating freely, Semi-submersible - not a monohull, Catamaran / CTV - not a monohull, SWATH - not a monohull. The closed-form theory behind this module is for monohulls; for these shapes it would produce a number without meaning.

PresetChoosing a preset fills in the values below; adjust any of them afterwards. What stands in the table is what the polar is computed against.

SeaData defaults (strict) — The values from ONDZ section 4, read as significant amplitude. Twice as strict as NORDFORSK.
NORDFORSK - intellectual work (bridge, survey) — Karppinen (1987) 3 deg and 0.10 g RMS, converted to significant amplitude (x2).
NORDFORSK - heavy manual work (deck, crane) — Karppinen (1987) 4 deg and 0.15 g RMS, converted to significant amplitude (x2). The transverse limit is the same 0.24 g as the lighter preset: NORDFORSK sets that one per vessel class, not per kind of work.

These are the limits the polar is coloured against: green below 0.8 of the limit, amber to 1.0, red above. The defaults for roll and vertical acceleration coincide with the NORDFORSK (1987) category "intellectual work" - bridge and survey work. Deck work and crane work sit at "heavy manual work": 0.15 g and 4 degrees.

Limit	Unit	Usual range
Roll significant what is this? Significant SINGLE roll amplitude in degrees - the swing to one side, not the double angle from rail to rail. NORDFORSK / Karppinen gives 3 deg RMS for intellectual work (bridge, survey) and 4 deg for heavy manual work; significant is twice RMS, so read as significant amplitudes those become 6 and 8 deg.	deg	2.0 – 5.0
Pitch significant what is this? Significant single pitch amplitude in degrees. It matters less than roll for people, but it dominates the vertical motion at points far forward or aft: a crane on the bow feels pitch, not roll.	deg	1.0 – 3.0
Heave at working point what is this? Significant vertical displacement amplitude AT THE WORKING POINT in metres - heave plus the pitch and roll lever arms, added in quadrature. The working point is the calculation point; with none entered on Vessel › 2D this is the centre of gravity, where it is heave alone and therefore always the friendliest number the ship can give.	m	0.5 – 1.5
Transverse acceleration what is this? Significant TRANSVERSE acceleration at the working point (the calculation point; the centre of gravity when it is empty), in g - what pushes a person or a load sideways, and the criterion that decides whether you can stand on a deck. It is the roll angle felt as a sideways force, and it has two parts that ADD: the component of gravity along a tilted deck (g x sin of the roll angle) and the swing of the lever arm above the roll axis. At 6 degrees of roll the gravity part alone is already 0.105 g, before a single metre of arm. NORDFORSK / Karppinen gives 0.12 g RMS at the bridge for merchant vessels and 0.10 g for naval and fast small craft; as a significant amplitude that is 0.24 g and 0.20 g. This figure needs the HEIGHT of the working point above the baseline - without it there is no lever arm and only the gravity part remains. Sway and yaw are NOT in it: this model has no sway or yaw response, so read it as the roll-driven part, which is the dominant one.	g	0.1 – 0.3
Vertical acceleration what is this? Significant vertical acceleration at the working point (the calculation point; the centre of gravity when it is empty), in g. This is the number that decides whether people can work and whether equipment holds its calibration. NORDFORSK / Karppinen: 0.10 g RMS for intellectual work and 0.15 g for heavy manual work, which read as significant amplitudes are 0.20 g and 0.30 g.	g	0.05 – 0.15
Hs ceiling what is this? A ceiling on the significant wave height whatever the motions do - the line in the operations manual or the contract that says we do not work above this. It does NOT depend on heading, so when this limit is the binding one the whole polar goes flat at a single value and turning the ship cannot help. That is worth recognising rather than mistaking for a broken plot.	m	0.5 – 6.0
Green water at the bow what is this? Probability PER WAVE that the sea comes over the bow: the relative motion at the stem (the ship against the wave, from the phase of heave and pitch) larger than the freeboard at the bow. NORDFORSK (1987) limits it at 0.05 for merchant ships and workboats. This is one of the effects the linear theory does not contain by itself; here it is counted explicitly, so a heading can close on it. The pile-up of the bow wave is NOT in it, so read it as a lower bound.	per wave	0.01 – 0.1
Slamming at the bow what is this? Probability PER WAVE of a bottom slam, after Ochi (1964): at 0.1 Lpp behind the stem the keel comes out of the water AND the relative velocity exceeds 0.093 x sqrt(g Lpp). NORDFORSK (1987) gives 0.03 for ships up to 100 m and 0.01 at 300 m. The draught at that station is taken as the mean draught.	per wave	0.01 – 0.05
Thrust utilisation what is this? How much of the thrust remaining AFTER the worst case failure the mean environmental forces may use, as a percentage. 80 is the usual figure and it is arithmetically the same as the 1.25 dynamic factor DNV-ST-0111 puts on the environmental forces to cover what a static balance leaves out (gusts, wave groups, control action).	%	50.0 – 100.0

Statistic

What happens between pressing Calculate and the polar appearing, where every number comes from, and where you should not trust it.

What this screen answers
Two chains under one polar
From five fields to a whole ship
Chain A - the motions
Chain B - station keeping
The calculation point
The top view, and the two sets of axes
Height, and the acceleration you feel sideways
The hull outline and your own drawing
Significant or RMS - the factor two that bites
The three plots, three views each
Where the weather comes from
External weather from your supplier
The confidence score
Where not to trust it
Sources

1What this screen answers

You give five things - vessel type, length, beam, draught, working speed - and press Calculate. The module takes the waves, wind and current for your position and the chosen hour, works out for 36 headings how the vessel sits, and colours each heading green, amber or red. Anything you did not fill in is estimated from the vessel type table and labelled as estimated.

There is no threshold at the front door: the module answers on five fields. What it will not do is hide how much of that answer it made up itself - that is what the confidence score is for, and every field you add replaces an estimate with a fact.

2Two chains under one polar

There are two ways the work can stop, and they have nothing to do with each other.

CHAIN A - MOTIONS. Does the vessel roll, pitch and heave too much to work? This is about the PEOPLE and the EQUIPMENT: a multibeam that stops measuring, a crane that can no longer be operated, a deck you can no longer stand on.
CHAIN B - STATION KEEPING. Can the vessel hold position and heading at all? This is about the SHIP: enough thrust against wind, current and wave drift.

Per heading the polar takes the WORSE of the two. A vessel that lies perfectly still but drifts off is no use to you, and neither is one that holds position perfectly while nobody can work.

ratio = max(chain A, chain B)

  < 0.8      green   workable
  0.8 - 1.0  amber   marginal
  > 1.0      red     not workable

Every sector also carries its LIMITER: which quantity closed it down - roll, pitch, heave, acceleration, Hs, or thrust in sway, surge or yaw. That is the most useful number on the screen, because it is the one you can act on: a different heading, a different working point, or waiting for the swell to turn rather than for the wind to drop.

3From five fields to a whole ship

Whatever you leave empty is filled in from the vessel type table. Your input always wins, and the module remembers per field which of the two it used.

Quantity	If you leave it empty
Cb	midpoint of the range for the vessel type
Cwp	2/3 Cb + 1/3 (Barrass)
GM	midpoint of the range for the vessel type
Displacement	Cb x Lpp x B x T x rho
Roll period	from the table - but if you entered GM yourself, T = 2 k B / sqrt(GM)
Freeboard	a fraction of the draught, per vessel type; measured from publicly published vessel dimensions
kxx, kyy	0.35-0.40 x B and 0.25 x Lpp, from the table
Awp	Cwp x Lpp x B
Roll damping	20 percent of critical

That one exception for the roll period is deliberate. If GM and the roll factor are both estimates from the same table, a computed roll period would contradict the roll period column of that same table - that is not an estimate any more, it is noise. So: real GM, compute the period from it; estimated GM, take the period straight from the table.

4Chain A - the motions

The frequency response functions are the closed-form expressions of Jensen, Mansour and Olsen (2004). The model replaces the vessel by a homogeneously loaded BOX of L x B x T with B = B0 x Cb, so that the mass is right. Heave and pitch are solved decoupled; for roll the model is two prismatic beams in line, because a single box does not capture roll at all.

From response to a number on the screen, in four steps:

WAVE SPECTRUM. JONSWAP with gamma = 3.3, rescaled so that the variance on the computational grid is exactly (Hs/4)^2 - without that rescaling a few percent of the energy disappears into the truncated tail and everything comes out too low.
DIRECTIONAL SPREADING. cos^2, zero beyond 90 degrees from the main direction, in nine steps.
PER HEADING. For every frequency and direction: the response, squared, times the spectral density. Summed that is the variance m0. The grid runs 0.10 to 2.20 rad/s in 72 steps - fine enough for the roll resonance of a container ship and wide enough for a workboat.
SIGNIFICANT AMPLITUDE = 2 x sqrt(m0). At the working point heave, pitch and roll add in quadrature, because they are independent in this decoupled model.

vertical^2  = heave^2 + (x . pitch)^2 + (y . roll)^2
acceleration = omega_e^2 . vertical

If the encounter period at the spectral peak falls within 15 percent of the natural roll period, the sector gets a RESONANCE MARK - the white arc in the polar. That is not an extra limit but a warning that this is where the model is at its most sensitive.

5Chain B - station keeping

THE WIND SPEED. The wind formulas below belong to a one-minute mean wind (IMCA M 140); a weather model gives the hourly mean. Station keeping therefore uses the GUSTS from the wind model, and when a model has no gusts the mean times 1.15. The Workability tab shows the mean, the gust and which of the two was used. Together with the 1.25 dynamic factor this is on the strict side. The same wind speed gives the wind heel on the Waves card (see WIND HEEL).

WIND HEEL. A steady side wind heels the ship, and the waves roll it about that heel. The Waves card therefore adds the heel to the roll before it is compared with the roll limit: wind force abeam (the gust, on the lateral area) times the lever from the centre of that area to half the draught, over displacement x g x GM - the set-up of the IMO weather criterion. The height of the centre is the field Wind area centroid height, otherwise your side view, otherwise (freeboard + 4) / 2.

UNDERWATER AREA. The current force abeam and the current yaw moment use the field Underwater lateral area when it is filled in (a keel or skeg adds to it), and Lpp x T otherwise.

ALL TOGETHER. Under the cards one line gives wind, current and wave drift at the same time, per heading. It is never lower than the worst driver alone: wind and current from opposite sides cancel in the sum, but a gust drops away while the current stays, so that cancelling is not counted on.

A STATIC force balance: mean wind, current and wave drift against the available thrust, over all 360 degrees - the method of IMCA M 140 and DNV-ST-0111. The thrusters are ALLOCATED PER HEADING: a linear programme looks for the largest multiple of the environmental load that the units can still hold together, each within its own direction (a tunnel only athwartships, a main propeller only fore and aft, an azimuth any way) and its own capacity, with every moment about the centre of gravity. The utilisation is one over that multiple. Unlike a sum per axis, an azimuth cannot push fully sideways and fully forward at the same time here.

THE WIND AREA comes from your own side view when a drawing is chosen: the area above the waterline under the upper outline of the drawing, and its centre gives the wind moment. Open structures count as solid, so the area is on the high side. The front area comes from the side and top view together. Without a drawing both are estimated from the freeboard. Wave drift is summed per sea component, each with its own height, period and direction.

wind     Fx = 1/2 rho_air V^2 . 0.423 cos(a) . A_frontal
         Fy = 1/2 rho_air V^2 . 0.800 sin(a) . A_lateral
         N  = 1/2 rho_air V^2 . -0.143 sin(2a) . A_lat . Lpp
current  reference areas B x T along, Lpp x T abeam
drift    F = (1/16) rho g Hs^2 L R
all environmental forces x 1.25 (DNV-ST-0111)

Thrust per kW is IMCA M 140: tunnel 0.145 kN/kW, azimuth ahead and main propeller 0.171, azimuth with reversed pitch and gill jet 0.105. After the worst case single failure what remains is DP1 100 percent, DP2 and DP3 50 percent - the IMCA default, overridable in step 4.

Watch outChain B is SKIPPED, with the reason on screen, when there are no thrusters entered. Then the polar is coloured on motions only and the Wind and Current cards stay empty - they are chain B and nothing else. Above zero working speed the numbers do appear, but with the caveat that a static balance at speed is a load figure and not a capability figure.

6The calculation point

The Waves card judges the motions at ONE point: the working point on Vessel › 2D. It is a calculation point, not necessarily a place where work is done - it is simply where heave, vertical acceleration and transverse acceleration are worked out and held against your limits.

Quantity	Where it is calculated
Roll, pitch	the whole ship - an angle is the same everywhere
Heave	at the working point: heave + pitch x arm along + roll x arm across
Vertical acceleration	at the working point, the same sum
Transverse acceleration	at the working point, with its height above the roll axis
Hs ceiling	the sea state itself, no point
Wind, Current, wave drift	about the centre of gravity - the working point plays no part

Watch outNo working point entered: the calculation point is the CENTRE OF GRAVITY. Only heave counts there and the transverse acceleration has no lever arm, so every result comes out at its mildest. The Workability tab names the point it used under "What it calculated with".

7The top view, and the two sets of axes

Vessel › 2D draws the ship you entered, seen from above, and it is where the geometry goes: the centre of gravity, the working point, and every thruster with its type and its power. Click the hull to place something, then correct the numbers - they are what counts, the click is only a way to get near.

You give positions the way a general arrangement gives them, and not the way the formulas want them.

y   along the ship, 0 = stern, y = Lpp at the stem
x   across the ship, 0 = centreline, + = starboard

the model then works with arms about the CoG:
    arm_x = y - y_cog     + = forward of the CoG
    arm_y = x - x_cog     + = starboard of the CoG

Watch outWatch the swap: the model's LENGTHWISE arm comes out of your y and its TRANSVERSE arm out of your x. That looks wrong and it is not - it is the difference between where a thing sits and how long its lever is. The conversion happens in one place in the code, so it cannot be reinvented differently somewhere else.

What the transverse position buys is not cosmetic. Two main propellers either side of the centreline hold a heading by running one ahead and one astern - the classic push/pull - and that is a real yaw moment of thrust times the distance off the centreline. Until a unit could be placed across the ship the model had no way to know about it and put it at zero. An azimuth unit was short-changed the other way: it can point its thrust anywhere, so the largest moment it can make is its thrust times its WHOLE distance from the centre of gravity, not just the lengthwise part of it.

The centre of gravity does the same work for the environment. The wind and current yaw coefficients of IMCA M 140 are referred to amidships, while the thruster arms are referred to the centre of gravity - two different pivots in the same fraction. The moment is now moved to the centre of gravity before the comparison is made. With the CoG 8 m aft of amidships and 600 kN of beam force on the hull, that is 4800 kNm that used to sit nowhere.

The outline itself is a drawing and not a lines plan, and it claims only what is true: it is Lpp long, B wide, and the area it encloses is EXACTLY the waterplane area Awp that chain A uses for the heave stiffness. The shape is solved from Cwp rather than drawn by hand, so a fuller hull on the screen means a fuller hull in the sum. At a common Cwp of 0.78 that construction gives a parabolic forebody - the waterline of a Wigley hull - which is why the two shape constants have the values they have.

Everything the geometry implies is listed under the drawing before any weather is fetched: per unit its thrust in kN, its two lever arms and the largest yaw moment it can make, and underneath the totals the ship can put into surge, sway and yaw after the worst case single failure. That is the table to watch while moving a unit around, and it needs no forecast at all.

Watch outThose totals are an upper bound per axis, not a thrust allocation. An azimuth unit is counted in full in surge, in sway AND in yaw, and in reality it cannot do all three at once. That is the Level 1 simplification of DNV-ST-0111 and IMCA M 140 - a sum per axis rather than a solved allocation per heading - so the capability is optimistic and the utilisation ratio in the polar is a lower bound.

8Height, and the acceleration you feel sideways

The vertical motion at a point does not contain its HEIGHT. That is not an opinion, it is the formula: the vertical acceleration at a point is heave plus the pitch and roll lever arms, and the height does not appear in it. So for as long as this module only judged vertical motion, there was nothing to ask a z coordinate for.

The TRANSVERSE acceleration is a different matter, and it is the one that decides whether a deck can be stood on. Two sources give it the same way - Journee & Massie eq. 8.59 and DNV Rules for Ships Pt.3 Ch.1 Sec.4 B701:

at = sqrt( ay^2 + (g sin(phi) + ary)^2 )

  g sin(phi)   the slope of a tilted deck, felt as a
               sideways push
  ary          the swing of the lever arm above the
               ROLL AXIS

WHERE THE ROLL AXIS SITS. With CoG z filled in (KG from the stability booklet, entered from the deck) the ship rolls about its centre of gravity - the usual assumption of linear seakeeping theory - and the roll axis is at KG. Without it, DNV Sec.4 B403 puts the axis at the smaller of D/4 + T/2 and D/2 above the baseline. Either way the lever arm is the height of the calculation point above that axis. Vessel › 2D says which of the two is used.

Watch outThe two terms ADD, they do not cancel. With phi = phi_a cos(wt) the roll acceleration is -w^2 phi_a cos(wt), so -zb phi'' + g phi comes out as (g + zb w^2) phi_a cos(wt). A point above the roll axis gets both the slope and the swing, in phase. At 6 degrees of roll the gravity term alone is already 0.105 g - close to the NORDFORSK limit of 0.12 g RMS before a single metre of arm is added.

What is NOT in it: sway and yaw. This model has no sway and no yaw response - the closed-form theory does not give them - so the figure is the ROLL-DRIVEN part of the transverse acceleration. DNV has that as the larger of the two terms, but it is not the whole of it, and the limit on the Limits tab says so.

Below the roll axis the two terms work against each other, and at a height of -g/w^2 they cancel completely. That is real, and it is the reason a sensitive instrument goes low and near the centreline rather than up on a deckhouse.

The height of a thruster does not enter the force balance at all - that balance has three degrees of freedom and none of them is vertical. What it does tell you is how deep the unit sits. Submergence is the draught minus the height, and a unit close to the surface draws air; a ventilating tunnel thruster loses more than half its thrust while it does. The module SAYS so and does not subtract anything, because a real ventilation criterion needs the propeller diameter and the wave elevation at the unit, and it has neither.

9The hull outline and your own drawing

Vessel › 2D has two orthographic windows, top view and side view, where a click resolves to exactly one number. Without a drawing they show the outline of the standard hull, stretched to your Lpp and beam. Upload your own top and side view as DXF and the windows draw THAT instead: nothing is built from it, it is only placed in ship coordinates - aligned to the aftmost and lowest line of the drawing, with a correction for where the transom and the baseline really are.

The hull is drawn as a generic OFFSHORE SUPPORT VESSEL, not as a lines plan of your ship: of any given ship this module knows a few dimensions and two coefficients, not a body plan. What it looks like is what a PSV of this size looks like:

a long parallel midbody with a near-rectangular midship section - flat bottom, small bilge radius, vertical sides
a wide, full transom with the bottom RISING towards it (a pram stern): that is where azimuth thrusters hang, under a flat, slightly sloping bottom
a flat keel far forward and a STRAIGHT rise of the bottom aft from about 0.3 Lpp, as on the general arrangements of the Damen PSV 3300 and the Ulstein PX121
round U-sections forward (no V), a rounded forefoot without a bulb, a near-vertical stem that leans slightly forward above the waterline, and FLARE that only starts high up towards the deck
a flat main deck over the full length and no superstructure

It carries one claim, checked by the self-test: the section AT THE WATERLINE is exactly the plan outline, so the area it encloses is exactly Awp. The length of the parallel midbody is solved from Cwp to get there - a fuller hull gets a longer one. The volume below the waterline is MEASURED and shown next to the view, not forced; for a PSV it comes out a few per cent under Cb x Lpp x B x T.

The drawn hull is a reference scaled to your main dimensions, not your lines plan, so a unit just outside it is not flagged. What IS ringed in red and named in the table is a position that cannot be right: behind the stern (y below zero), more than 10 per cent of Lpp forward of the bow, outside the beam, or at or above the waterline for this draught.

Two waterlines can be drawn, and two centres of gravity: the loading condition you are computing, and the other one. The second set is REFERENCE ONLY - nothing in the calculation touches it. What it answers is the question one waterline cannot: a bow tunnel with nine metres of water over it when loaded may have two when light, and that is the trip on which it ventilates.

10Significant or RMS - the factor two that bites

This is the pitfall of the whole module. The output is the SIGNIFICANT amplitude, 2 x sqrt(m0). The NORDFORSK / Karppinen table the default values come from states its figures as RMS, sqrt(m0). Significant is therefore twice RMS.

The SeaData defaults - roll 3 degrees, acceleration 0.10 g - are numerically equal to the NORDFORSK figures for intellectual work, but those are RMS. Read as significant amplitudes our defaults are therefore TWICE AS STRICT as NORDFORSK. That is not wrong, but it has to be a choice, which is why the Limits tab offers all three:

Preset	Roll	Pitch	Heave	Acceleration
SeaData defaults (strict)	3 deg	2 deg	1.0 m	0.10 g
NORDFORSK intellectual work	6 deg	3 deg	1.0 m	0.20 g
NORDFORSK heavy manual work	8 deg	4 deg	1.5 m	0.30 g

All values are significant amplitudes; the NORDFORSK rows are the published RMS values multiplied by two. Survey and bridge work belongs on the middle row, deck and crane work on the bottom one.

11The three plots, three views each

One polar tells you THAT it is tight. Three tell you WHAT is doing it - and that is the difference between waiting for the swell to drop and waiting for the wind to drop.

Plot	What it shows	Available when
Waves	motions from the sea state, plus wave drift	always
Wind	station keeping against wind alone	wind data present and thrusters known
Current	station keeping against current alone	current data present and thrusters known

Each card has three views. POLAR answers which heading - heading is cyclic, so a circle is the honest shape for it. BARS answers how much exactly, because comparing two headings by eye on a circle never quite works. TABLE is not a fallback: it is the guarantee that every number is reachable in text, for a screen reader, for a report, and for anyone whose colour vision the palette cannot serve.

Watch outThe Wind and Current cards carry no motion component at all. A green Wind card does not mean you can work in that wind; it means the wind alone will not push you off position. Read the three cards together: a heading is only workable when it is green on all of them.

12Where the weather comes from

The browser fetches the wave, wind and current data for your position, walks the model ranking per quantity and takes the first source that has data - exactly the same ranking the SeaWave, SeaWind and SeaCurrent tabs use. The table "What it calculated with" names the winning model per quantity.

That is deliberate. If the server fetched the same data by a second route, screen and calculation could drift apart without anyone noticing. As it stands, the number you see on your screen is the number it computed with. Which sources those are, and under which licence, is on the Data sources page at /bronvermelding.

DIRECTIONS. Wind and waves carry coming-from; a current curve carries going-to. 180 degrees is added before the current enters the calculation - without that the current force points exactly the wrong way.
TIMESTAMPS. The curves do not all start at the same hour, so matching is done on timestamp and never on index.
PARTITIONS. Wind sea and swell are computed as two separate peaks as soon as the source gives a PERIOD per partition (a peak period, or a mean period Tm01 that is converted with the shape of the spectrum itself). The model sources on the platform today give the partition heights but not their periods, so for now the spectrum is usually one peak - and a low swell across the heading is then under-represented.
SWAN COMES FIRST. For "now" the waves come from the SWAN run at your position whenever there is one: its Hs, peak period and peak direction, and also the SHAPE of the sea - the peakedness Qp becomes the JONSWAP gamma, the directional spread DSPR becomes the width of the spreading. With no run yet, or a run older than 30 minutes, Calculate starts a fresh one (about 30 seconds). The model only takes over when SWAN cannot give an answer: a forecast hour (SWAN is a snapshot of now), a position outside the SWAN coverage, a very sheltered or shallow spot (Hs under 5 cm or less than 2 m of water), or no result within 60 seconds. The Workability tab always says which of the two was used, and when it is the model, why SWAN was not. The water depth from SWAN is shown, not used: the motion theory here is deep water.

THE SHAPE PER COMPONENT, without SWAN: gamma from DNV-RP-C205 3.5.5.5 (5 for a steep sea, 1 for a long one, from Tp / sqrt(Hs)); spreading cos^2 for wind sea (31.5 degrees) and a narrow swell with the spread of Mitsuyasu cos^2s(theta/2) at s = 25 (Goda), 15.9 degrees. The Workability tab lists gamma and spread per component under "What it calculated with".

13External weather from your supplier

Your contract may oblige you to use a commercial forecast (DTN, StormGeo, Infoplaza). External weather reads that PDF and draws it next to our models. It is a line, never a vote: the go / no-go stays the average of our best three models.

Upload the PDF, or e-mail it to weather@wx.seadata.online from a sender address you have set in External weather.
Only the table is read, from the text layer of the PDF: time, wave, wind, current, visibility, units and time zone, converted to metres, m/s and UTC. A unit that does not match what the supplier normally prints means the file is refused, not guessed.
Up to 50 km from the vessel you can release it (Use in SeaData) and it appears in Reporting. From 50 to 100 km it is only plotted in External weather, with a warning. Beyond 100 km it is read but not plotted.
The box holds 10 reports, each for 72 hours, at most 2 MB per PDF. Refused mail is bounced; the reason is in Profile, Notifications.

Watch outA supplier forecast is a point forecast for the position in the document, not for your vessel. That is why the distance is always shown, and why a far-away point is never used.

14The confidence score

Three parts, 100 together.

VESSEL DATA, 50. Points per filled field, weighted by how sensitive the answer is to it: GM or roll period 15, roll damping 10, working point 8, Cb or displacement 5, thrusters 5, kxx/kyy 4, freeboard 3. Step 1 alone scores zero.
ENVIRONMENT, 30. A full 2D spectrum scores highest, a model forecast with wind sea and swell separated in the middle, and a total Hs and Tp alone the least. From +6 hours a point comes off per hour, with 5 as the floor.
VALIDITY OF THE THEORY, 20. Hs below Lpp/25 scores full, up to Lpp/20 scores half with a warning, above that zero with the note that it is outside the linear range.

The number matters less than the line beneath it. "Improve by adding" names the three missing fields that gain the most, and that is the part you can act on. Below 40 the result is an indication, not a prediction.

15Where not to trust it

Watch outTHE ROLL DAMPING IS THE WEAK SPOT. At roll resonance the wave damping practically vanishes, so the viscous damping decides the answer on its own - and a factor 2 in damping is a factor 2 in roll angle. The absolute roll level is not proven either: it sits roughly 2.7 times above a quasi-static cross-check, and the source paper itself reports that the method over-predicts roll. For a workability call that errs the right way - it says do not work sooner rather than later - but expect the polar to be stricter than reality near resonance.

Heave and pitch: linear theory, indicative above Hs of about Lpp/20. Roll: the viscous damping is linearised for the sea state (ITTC 7.5-02-07-04.5) - half linear, half quadratic, equal to the entered damping at 6 degrees significant roll. That split is an assumption until a roll decay test of the ship exists.
No parametric roll. Green water and slamming are probabilities per wave from the relative motion at the bow (deck wetness above the freeboard at the bow; slamming after Ochi 1964), without the pile-up of the bow wave - read them as a lower bound.
Station keeping is static: mean forces, no dynamic DP control, no thruster interaction or ventilation, no forbidden zones. The worst case failure lowers every unit by the same percentage instead of removing a specific one.
The current coefficients and the wave drift reflection factor are rules of thumb without a free source.
In following seas the encounter frequency can approach zero; it is clipped at 0.05 rad/s.
Monohulls only. The theory is closed-form strip theory, and for the hull forms listed under Vessel › Config it would produce a number with no meaning.

If a result looks wrong, work through this order: is the limiter roll and is there a resonance mark - then a different heading helps more than waiting. Is GM estimated - then the roll period is a table value and can be seconds off. Is the strict preset still selected for deck work. Does station keeping say skipped. And finally: what does the score say.

16Sources

Every number in this module comes from one of these, or it is a rule of thumb - and the Status column says which. Where a source could not be obtained that is written down as well, because a figure nobody could check is worth knowing about before you plan a day around it.

Motions - chain A

Source	What we take from it	Status
J.J. Jensen, A.E. Mansour, A.S. Olsen, "Estimation of ship motions using closed-form expressions", Ocean Engineering 31 (2004) 61-85, doi:10.1016/S0029-8018(03)00108-2purchased; the PDF is on the SeaData server	Every response function in chain A: heave, pitch and roll, the box model with B = B0 x Cb, and the viscous damping as a fraction of critical. Each formula in the code carries its equation number from this paper.	primary source, implemented and tested against the paper's own worked example
U.D. Nielsen et al., "Sea State Estimation Using Vessel Response in Dynamic Positioning", section 2.3open access, DTU Orbit	Independent confirmation of the set-up and of the input list the method needs; the roll radius rx = 0.4 B after Papanikolaou.	confirmed
R. Grin, "On empirical methods to predict the rolling period of ships", IMDC-2024, Amsterdamopen access, TU Delft proceedings	The roll period T = 2 k B / sqrt(GM) and the class society table of roll factors k: Lloyd's 0.41, DNV 0.45 and 0.40, ABS 0.40, ClassNK 0.40, BV 0.39 and 0.33, IACS 0.40 to 0.52, Lewis 0.36. Range 0.33 to 0.52, mean 0.42.	confirmed; our kxx values sit at the LOW end of this range and therefore give a short roll period
C.B. Barrass, "Ship Design and Performance for Masters and Mates", chapter 1free sample chapter, Elsevier	Typical block coefficients per ship type, and Cwp = 2/3 Cb + 1/3.	confirmed for the merchant types; NO source found for Cb of survey, PSV, AHTS, CSV or dredger hulls
ITTC Recommended Procedure 7.5-02-07-04.5, "Estimation of Roll Damping"free, ittc.info	Read in full to find typical roll damping as a percentage of critical. It gives only a component method (Ikeda) and no such table.	NOT found - the damping percentages behind the tick boxes remain rules of thumb, and this is the largest uncertainty in the module
DNV-RP-C205, October 2010 edition, section 7.1.3.6free, rules.dnv.com	Defines the roll and pitch radii of gyration r44 and r55 in the natural period formulas.	definition confirmed; gives no typical values for ships, so kyy as a fraction of Lpp has no source
M. Zu et al., "Seakeeping criteria revisited", Ocean Engineering 297 (2024) 116785, tables 4 and 5 - reproducing Karppinen (1987), adopted in NORDFORSK (1987)open access, KTH	The motion criteria per work category that the limit presets are built on: intellectual work 0.10 g and 3 deg, heavy manual work 0.15 g and 4 deg, light manual work 0.20 g and 6 deg.	confirmed - and the source states these as RMS, which is why the presets double them

Station keeping - chain B

Source	What we take from it	Status
IMCA M 140 Rev. 1, "Specification for DP Capability Plots", June 2000freely available	Thrust per kW per thruster type (sections 2.1-2.5), the wind force formulas and coefficients (appendix 1 section 2), the current force formulas and reference areas (appendix 1 section 4), and the worst case failure assumption of half the thrusters (section 3).	confirmed, quoted literally in the research log; note it dates from 2000 and uses API RP2SK wind coefficients
DNV-ST-0111, "Assessment of station keeping capability of DP vessels" - via Karlsen et al. (MTS DP Conference 2016) and Pivano et al. (2017)the standard itself is paid; both conference papers are free	The Level 1 definition (a static balance of environmental and actuator forces) and the dynamic factor of 1.25 on the environmental forces, which is arithmetically the 80 percent utilisation limit.	method and the 1.25 confirmed; the literal Level 1 formulas and coefficient tables are behind the paywall
U. Nienhuis, "Simulation of Low Frequency Motions of Dynamically Positioned Offshore Structures", RINA, 1986not freely available	The current force coefficients IMCA M 140 refers to.	NOT obtained - the current coefficients 0.10 along and 0.80 abeam are rules of thumb
OCIMF MEG4paid	Cross-check on the reference area convention for current forces.	convention confirmed indirectly; the tables themselves not obtained

The top view and the thruster layout

Source	What we take from it	Status
IMCA M 140 Rev. 1 (June 2000), "Specification for DP Capability Plots", Appendix 1 section 1 and sections 2.1-2.6, 3free PDF, on the SeaData server in PDF-info	The axis system and the fact that the wind and current yaw coefficients are referred to amidships; the thrust per unit power per type (tunnel 11 kg/hp, rotatable 13 ahead and 8 with reversed pitch, main propeller 13, gill jet 8); that a gill jet is to be treated as a ROTATABLE unit and not as a transverse one; that the worst case single failure is normally the loss of one engine room and with it half the thrusters, and that what remains must give thrust both fore-aft and athwartships.	confirmed in the document itself; the gill jet was on the wrong side of that line until v1.3 of mod_dpcap
R. Nordtveit (Teekay), "Thrust Degradation in DP Operations", MTS DP Conference, Houston, October 2007free PDF, on the SeaData server in PDF-info	Model-measured thrust reduction coefficients: main propeller 0.85 loaded and 0.75 in ballast, tunnel thruster 0.80 and 0.65; ventilation of a tunnel unit can take over 50 percent for short periods; barred azimuth sectors follow from the propeller disc diameter and the spacing to the neighbouring unit, and in the measurements 0-30 degrees on one bow unit had to be barred.	read and confirmed, NOT YET APPLIED. These figures belong to one hull in one sea area and include wave and ventilation losses, so using them as a general factor would trade a known optimism for an unknown one. The module therefore still assumes the IMCA figures and says so.
N. Bulten, P. Stoltenkamp, "Improved DP-capability with tilted thruster units and smart thrust allocation", MTS DP Conference 2016free PDF, on the SeaData server in PDF-info	Thruster-hull interaction and the forbidden zones that follow from thruster-thruster interaction; that the allocation algorithm itself is a first-order effect on the capability plot.	read, NOT applied - the loss figures are CFD results for specific thruster units and hull forms and do not generalise to an unknown ship
Tunnel thruster effectiveness against forward speedmanufacturer and patent literature, consulted 2026-09-12	Indication of how much a tunnel unit loses under way: roughly a quarter of its thrust by 3 kn and about half by 7 kn, worst between 4 and 6 kn.	NOT applied. The figures in the literature range from a few percent to ninety, depending entirely on how they were measured, and a static capability balance is defined at zero speed in any case. Above zero working speed the module states a caveat rather than a correction.

Height, the roll axis and the transverse acceleration

Source	What we take from it	Status
DNV, "Rules for Ships", January 2012, Pt.3 Ch.1 Sec.4 B (Ship Motions and Accelerations)free PDF from DNV's own rule server; on the SeaData server in PDF-info, with a reading note in BRON_dnv_rules_ships.md	The roll axis at the smaller of D/4 + T/2 and D/2 above the baseline (B403), and the combined transverse acceleration at = sqrt(ay^2 + (g sin phi + ary)^2) with ary taken on the VERTICAL projection of the arm (B701). That pair is what makes a height mean something.	confirmed, and read off the RENDERED pages: the text layer of those 190 pages holds exactly one radical sign, so the roots are drawn and pdftotext loses them - which already caught one thing, the pitch angle has no root where heave and surge do
J.M.J. Journee, W.W. Massie, "Offshore Hydromechanics", TU Delft, section 8.4.2open textbook, TU Delft OCW; on the SeaData server in PDF-info	The full derivation of the accelerations at a point: eq. 8.59 for lateral (with the -zb phi'' and +g phi terms) and eq. 8.60 for vertical - in which the height does NOT appear, which is why this module never needed z before. Also the operability table in chapter 11 with the same NORDFORSK lateral figures.	confirmed; this is the source CalQlata cites as its reference 43, and it gives the derivation where a class rule gives only the result
M. Zu et al., "Seakeeping criteria revisited", Ocean Engineering 297 (2024) 116785, table 4open access via the KTH repository; on the SeaData server in PDF-info	NORDFORSK / Karppinen (1987) in full, including the LATERAL acceleration this module had no limit for: 0.12 g RMS at the bridge for merchant vessels, 0.10 g for naval vessels and fast small craft. As significant amplitudes that is 0.24 g and 0.20 g.	confirmed, and stated as RMS. Mind that the paper's own text mentions 0.15 g for merchant vessels where its table says 0.12 g - that spread is in the source, so use the figure as an order and not as a boundary to two decimals
CalQlata, "Vessel Motion Calculator" help pageweb page, consulted 2026-09-12; saved with a reading note in PDF-info/BRON_calqlata_vessel_motion.md	Independent confirmation that positions are conventionally given from the aft perpendicular and the baseline, and a pointer to the two sources above.	SIGNPOST ONLY, not a primary source. It cites "DnV RP B401" for ship motions, which is the recommended practice for cathodic protection, and it writes the combined acceleration as a PRODUCT of squares where it is a sum. Everything taken from it was checked against the sources it names

Thruster types

Source	What we take from it	Status
IMCA M 140 Rev. 1, sections 2.1 to 2.6free PDF, on the SeaData server in PDF-info	Thrust per unit power per type, and two rules that decide what a type can DO: a gill jet counts as a rotatable unit (s2.3), and a rudder that takes part in DP counts as a TUNNEL thruster at the rudder stock, with 30 percent of the maximum astern thrust of one propeller when no figures are available (s2.4) - which with the 70 percent astern limit of s2.5 gives 0.30 x 0.70 x 0.171 = 0.0359 kN/kW of the PROPELLER's power.	confirmed, quoted literally
D. Jurgens, M. Palm, "Voith Schneider Propeller - An Efficient Propulsion System for DP Controlled Vessels", MTS DP Conference 2009free PDF, on the SeaData server in PDF-info	That a cycloidal unit steers its thrust through zero in any direction - so it counts as rotatable - and that it is LESS prone to thrust losses from ventilation than a thruster-type propeller.	confirmed for the behaviour, but NO thrust-per-power figure found in it or anywhere else. The Voith therefore carries the rotatable figure of IMCA s2.2 and that is stated in the table. The ventilation finding is used only to make the submergence warning milder for it - nothing is taken off the thrust, for a cycloidal unit or any other

Vessel types and hull forms

Source	What we take from it	Status
Public fleet data - 82 published equipment pages, consulted 2026-09-08publicly available vessel specifications; the raw result is kept on the server	Measured length/beam, beam/draught and freeboard/draught per type across the 53 vessels that publish dimensions, and the common industry category names for the five dredging and offshore types.	measured, n per type is stated in the research log; jack-ups and two inland dredgers were excluded on purpose
The same public data, for hydrostatics-	Block coefficient, GM, roll period and radii of gyration per vessel.	NOT obtainable: of 82 pages exactly one states a displacement, and GM, roll period and radii belong to the loading condition rather than to the ship - which is exactly why this module asks the user for them
Damen Platform Supply Vessel 3300 CD, product leaflet with general arrangement (side view, main deck, tween deck), consulted 2026-09-13publicly available	Reference for the drawn hull: 80.1 m length, 16.2 m beam, 7.5 m moulded depth, two azimuthing thrusters aft. The side view gives the flat keel, the straight rise of the bottom aft from about 0.34 L and the forefoot; the deck plans give the full-width deck to about 0.75 L and the pointed, convex bow.	confirmed as a drawing; the shape parameters (bilge radius, transom height, stem rake, flare) are read off it by eye, not measured
Ulstein PX121 H, vessel introduction (resale brochure) and specification U10782, consulted 2026-09-13publicly available	Second reference: profile with flat keel and rising stern bottom, and the section at frame 0 through the azimuth unit - a flat, sloping bottom with the pod hanging below it, no skeg.	confirmed as a drawing; the X-BOW itself is not modelled

Environment

Source	What we take from it	Status
The wave, wind and current sources of the SeaData platformlisted in full, with licence and required attribution, on the Data sources page at /bronvermelding	Hs, Tp and wave direction, wind speed and direction, current speed and direction for your position and hour - taken through the same ranking the SeaWave, SeaWind and SeaCurrent tabs use, so that the number on the screen is the number computed with.	per source; the winning model per quantity is named under "What it calculated with"

Over SeaData

Elk zeegebied heeft zijn eigen humeur. Het getij dat een uur verloopt over twintig mijl, een stroom die kentert terwijl de wind doorzet, een deining die van ver komt aanzetten. De meeste bronnen vatten dat samen in tabellen voor een heel gebied. SeaData doet het omgekeerde: het rekent getij, getijstroom, golven en wind uit voor précies de positie waar jouw schip ligt — en die data vaart met je mee.

Waarom SeaData:

Alleen officiële bronnen. Getij en waterstand van de hydrografische diensten zelf — Rijkswaterstaat, DMI, MET Norway, SMHI, BSH, Environment Agency en SHOM. Meet SeaData het niet en geeft een dienst het niet uit, dan staat het er niet.
Modellen van naam. Stroming en waterstand uit Copernicus Marine (CMEMS) en het Met Office NWS-model, golven uit WAM en WAVEWATCH III, wind uit ECMWF, ICON en HARMONIE, en getij uit de wetenschappelijke modellen EOT20, FES2022 en DTU23.
Gemeten waar het kan. Boeien en meetpalen van de Noordzee tot de Oostzee — Meetnet Vlaamse Banken, KNMI, CANDHIS en de nationale meetnetten — zodat je naast de verwachting ook ziet wat er werkelijk staat.
Je ziet wáár het vandaan komt. Elke waarde draagt zijn herkomst: gemeten, officieel of berekend. Verschillen tussen modellen worden getoond, niet weggepoetst — want die zeggen iets over de zekerheid van het beeld.
Alles op één kaart. Getij, stroom, golven, wind, regenradar en AIS in één beeld aan boord — geen losse sites en apps meer naast elkaar.

Maak een account aan en vaar met je eigen data.

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Ask about SeaData

197 questions answered. Type a question, or tap one below.

Grey means that layer or button is not active/not being drawn. For example, a dimmed flag or grey button in Map layer means that layer is switched off; normal (not grey) means it's on. Note that folding a block away (like Overlay or Tide stations) never greys anything out, since folding doesn't switch layers off - it just tucks the panel out of view.

SeaData is a maritime data platform. It pulls waves, wind, current, tide, rain radar and AIS traffic from official sources and shows them at the position of your vessel, on one map.

Sign in, then pick your vessel with the Vessels button at the top left. Everything else follows that position: open a side tab on the left for waves, current, wind, tide or Workability, or press the eye button top right for a quick Overview.

For your own vessel, yes. Without an account the map shows a fixed demo position, the Workability tab shows the Demo vessel, and Try it in the bottom bar lets you follow one MMSI for half an hour. With an account the data follows your ship.

Use the Login button in the bottom bar. After signing in the map follows your vessel.

SeaData is in beta. For questions about pricing and plans, contact us - that is not something this guide can answer for your situation.

A browser. There is nothing to install. It works on a laptop, a tablet and a phone, though the map is easier to read on a big screen.

No. Every reading is fetched live, so you need a connection. On a poor link the map still loads but panels may take longer to fill.

English and Dutch. Switch under the cog in the top bar, at Language; the choice is remembered. Buttons and tabs are in English in both.

Yes. The layout adapts: the side tabs move to a row and the panels fill the screen. The map controls sit in the corners.

If no vessel position is known, SeaData falls back to a fixed spot in the North Sea so the panels have something to show. It is clearly marked - the data is real, the position is not yours.

Top right, under Map layer, there is a dropdown with OSM, Voyager, Ocean and Topo. Ocean and Topo show depth and terrain; OSM shows the most detail ashore.

Dashed rectangles showing which forecast model covers which sea. The EU flag under Map layer switches them on and off. Where two models overlap, the finer one is used.

Click the SeaRain tab on the left; it switches our own rain layer on and off. The small cog in that tab sets the region (Europe, Asia or World), the quality and the extras. The old Radar buttons with country flags are gone.

Two possible reasons: there is no precipitation, or no radar reaches that far - radar stops a few hundred km off the coast. In the SeaRain settings choose World: that is a satellite estimate and the only one that covers the open ocean.

Bottom right, click Waves. The sea is coloured by significant wave height and the scale appears right under the button.

Bottom right, click Wind. Same idea as waves: the sea is coloured by wind speed with the scale underneath.

Bottom left, each flag switches the tide stations of that country on or off. Handy if you only care about the coast you are on.

It folds the whole bottom-right block away, so the map is clear. It does not switch anything off - what was drawn stays drawn.

Grey means that layer is not being drawn. Normal means it is. Folding a block away never greys anything out, because folding does not switch layers off.

Click the Overlay icon bottom right or the Tide stations icon bottom left. The triangle shows whether a block is open or folded.

Not yet. The circle around your vessel gives a sense of scale, and the position readout at the bottom follows your cursor.

A range ring around your vessel, so you can judge distances on the map at a glance.

The crosshair button in the top bar, next to the vessel name. It brings your ship back into view at about a 50 km range.

Because no real position is known yet. It stays grey until your vessel appears in the AIS feed - centring on a made-up position is worse than not centring.

Measuring stations: buoys, tide gauges and weather platforms. Hover for a summary, click for the full reading.

The shape says what kind of station it is - offshore platform, island station or coastal gauge. Colour and flag say which country.

Colour shows how the tide for that harbour is derived and how far away it is. A grey dot means it is computed rather than measured.

Not on the map itself. Pan and zoom, or use the vessel button to jump back to your ship.

Your vessel position is in the top bar; the bottom bar shows the position under your cursor. The cog in the top bar sets the format - decimal degrees, or degrees and decimal minutes.

On Fleet+ and Fleet admin, yes: the bullseye button in the bottom bar drops your own point instead of following the ship. While it is on, the button is yellow and the map shows a yellow ChartPos warning - the data is then for that spot, not for your vessel.

It sets how many arrows are drawn for that layer. All the way right is the densest useful setting - arrows about one arrow width apart. All the way left draws none. Waves and Wind have their own slider, and the setting is remembered on this device.

Because the spacing is measured on your screen, not on the chart. Zoomed out you would otherwise get thousands of arrows on one heap, and zoomed in almost none. The arrows you do not see are not calculated either, so zooming out does not make the map slower.

SeaWave, SeaCurrent, SeaWind, SeaTide, SolarNav, SeaHarbour and Workability open a panel for your position. AIS, ForeCast and SeaRain are switches: they put a layer on the map and open no panel.

The clock button in the top bar opens Data status: one ring per source, grouped as Wave, Wind + Warnings, Current, Tide, Observations and Radar. A ring is one refresh cycle. It starts full and green just after a refresh and drains toward red as the cycle runs out; red also means the source is missing or overdue. So one glance tells you which feeds are current and which are lagging.

Click the same tab again, or the cross in the top right of the panel. Clicking a different tab switches straight to that one.

Wave conditions at your position: significant height, period and direction, from several models side by side so you can see where they agree.

Current at your position - total, tidal and residual - with a profile with depth where the model provides it.

Wind speed, gusts and direction from several models, plus a multi-day outlook.

Water level over time: measured where a station is near, official predictions where a service publishes them, and harmonic computation elsewhere.

Sun and moon data for your position: rise, set, twilight and elevation - useful for planning watches and for celestial work.

Two tabs. Port info: harbour information from the World Port Index for every sea port a vessel of 50 m or more can use, with size limits, depths, pilotage, tugs and facilities. Tide ports: every tide port with the level now and the next high and low water.

Official warnings and notices for the sea areas you are sailing in. It is a map layer, not a panel: the tab switches it on and off.

A switch: it puts our own AIS layer on the map, or takes it off. It no longer opens a panel or an external traffic map. Zoomed out you see your own fleet only; zoom in to see every vessel in view.

A dash means no model covers that point, or the value has not been fetched yet. It is deliberately not a zero - no data and a value of zero are different things.

The finest model that actually covers your position. Panels name the source per row, so you can always see where a number came from.

It varies per model and per parameter, from about two days to over a week. The charts show the range each model provides.

The charts start at midnight UTC of the current day, so you see today's run up to now. Longer archives are not part of the platform.

So every chart shares the same time axis and you can lay them side by side. The vertical line marks now.

Now, in UTC. It moves right through the day.

Not from the panels. The API is the route for that, with your API key.

The part of the current that is not tide - wind driven and density driven flow. Total current minus tidal current.

Current at several depths instead of just the surface, where the model provides it. Useful for a deep draught or for towed gear.

Sea surface temperature at your position, from the same models as the current.

Wave models have a grid, and close inshore a cell may be partly land. The finer models reach further in than the coarse ones.

The model does cover your position, but you are close to the edge of its area. The values are usable; treat them with a little more care.

A small program that runs on a PC on board. It listens to the ship's NMEA network and sends what it hears to SeaData about every six seconds, over ordinary https on port 443. Outbound only: nothing has to be opened up on board, and nothing is sent back to the ship. You download it on the API tab of your account, next to your key.

Yes. The key is what tells SeaData whose vessel this is, so it goes in the program's settings on board together with the MMSI. On top of that the vessel must be ticked 'Position via SeaData.exe' in your fleet. Without that tick the server refuses the data on purpose - otherwise you would be sending for months to a vessel you only think is working.

Where AIS does not reach, yes. Shore stations only hear you near the coast and the satellite feeds are minutes to hours old. A vessel that sends its own position stays on the map in those gaps, and does so every six seconds instead of every few minutes. Its position sits on top of shore AIS, because a vessel knows where it is better than a coastal station does. Shore AIS stays as the fallback: switch the program off and the vessel falls back to it by itself.

Position, speed over ground, course and time, plus heading from the gyro, roll, pitch and heave, true and relative wind, air pressure, temperature, humidity and dew point, and depth once an echo sounder is connected. Which of these arrive is ticked per sentence in the program on board. Today the platform uses the position; the rest is kept for six hours so it can be looked at and is not yet part of any calculation.

The tab that shows what your own vessel is sending in. It says whether the link is alive (a ring that fills with every burst), what came in, the last six hours as a graph, the last message line by line, and any refused bursts with the reason. It needs SeaData.exe running on board and your API key set; the demo screen has no vessel of its own, so it stays empty there.

Check three things, in this order: the API key in the program on board matches the one on your account (a wrong key is refused with 401 or 403), the MMSI is in your fleet, and the vessel is ticked 'Position via SeaData.exe'. If the bursts arrive but are refused with 400, there was no usable position in them - if the GNSS drops out the whole burst is refused, including wind and motion. The Vessel Online tab lists the refusals with their reason.

Six hours, and that is the whole memory: it is a window that moves along with the vessel, so anything older falls off. It is kept in a file per vessel and nothing of it goes into the database. A restart of the website does not clear it, but it is never an archive.

Because the vessel does not send it. Current can only be measured on board from $VDR (set and drift) or $VBW (speed through the water), and neither is in the feed. What you see for current elsewhere in SeaData comes from the models (CMEMS, DKSS, DCSMv7, with FES filling the gaps), not from your ship.

A route planner that answers what the weather does on the way, at the hour you are actually there. You set waypoints on the map; Transit then samples wave, wind and current along the route, works out the passage with the tidal current in it and tests it against your Contract limits. It runs the same route twice: at the speed you set and at the speed the vessel is really making. The route stands still once made; your vessel is a point on it.

In your profile, under Vessels, or under the cog in the top bar at AIS vessel (MMSI). Enter the MMSI; the name and position follow from the AIS feed once your ship is heard.

The nine-digit identity your AIS transponder broadcasts. It is how SeaData recognises your ship among all the others.

Three usual causes: the MMSI is wrong, your transponder is off, or you are outside the coverage of the receiving network. AIS is picked up by shore stations and satellites, and mid-ocean gaps are normal.

Fix age in the top bar shows the age of the last fix, coloured green, yellow, orange or red. Positions older than forty minutes are dropped, because a stale position on a map is worse than no position.

It depends on your account type. One vessel on a single account, more on a fleet account. Your profile shows how many slots you have and how many are in use.

Either all slots are in use, or a slot you freed up is still on hold. A released slot stays reserved for a while, otherwise the limit would mean nothing.

In your profile, under Vessels, with the cross next to the ship. Note that the slot does not come free straight away.

The Vessels button at the top left. The one you pick becomes the active vessel and all data follows it.

Ship type: cargo, tanker, passenger, high-speed, tug, fishing, sailing and so on. The legend sits with the AIS layer.

A ship broadcasts its identity less often than its position. Until that message arrives, only the MMSI is known.

Your ship broadcasts AIS publicly, so it is visible to anyone with a receiver - that is how AIS works, and not something SeaData decides. Your account and your settings are not public.

No. Only the last known position is kept, overwritten each time. There is no sailing history.

Registrations are released by hand at the moment. You get a message once it has been done.

Email delivery is not reliable at the moment, which is exactly why approval is done by hand. Your request is in the queue - you do not need to do anything.

Use the password request option on the sign-in page. It raises a notice for the administrator, who will help you further.

No, and that is on purpose. Only a hashed version is stored, which cannot be turned back into your password. That is also why a leaked backup would not expose it. A reset is the only route.

One session per account. If someone signs in elsewhere with your details, your session ends. If that was not you, change your password.

Technically you would keep signing each other out, because only one session per account is active. Practically: no.

No. The session is not tied to an IP, precisely because a ship switches between 4G, VSAT and harbour wifi all day.

In your profile, on the Account tab. Save at the bottom.

It identifies your account for programmatic access. Keep it to yourself - anyone holding it can make requests in your name.

In your profile, on the API tab. Generating a new one immediately invalidates the old.

After a long period without use an account is deactivated, with a warning first. Reactivating is possible.

Official services: Copernicus Marine, the Met Office, KNMI, DMI, Meteo-France, AEMET, IPMA, Rijkswaterstaat and others, plus tide models such as FES, EOT20 and DTU23. Every panel names its source.

Where a station measures nearby, very. Where an official service publishes a prediction, close. Where it is computed from harmonics, it is a model - good in open water, less so in a narrow estuary.

Measured is a real gauge reading. Official is a prediction published by a national service. Computed is our own harmonic sum. In that order of confidence.

Because they are different models with different grids and physics. Seeing them side by side is the point: agreement is reassuring, disagreement tells you the situation is uncertain.

The bottom bar has three rings: SeaWave consensus, SeaWind consensus and S.W.A.N consensus. Each reads the models for your position and shows how well they agree; the S.W.A.N ring compares SWAN with the average of the other models. The button with the arrow picks the moment - now, +3, +6, +9 or +12 hours - fixed steps, because the models only publish every few hours and anything in between would fake a precision that is not there.

The readings come from the CWA (Central Weather Administration) open-data feed for Taiwan, one call that returns all its coastal stations at once - the sea state as it stands now, not a forecast. The feed gives a station id but no position, so each station is placed from a separate station list that maps that id to a name and a latitude and longitude. A station that reports nothing is left blank rather than guessed.

Six feeds from the JMA (Japan Meteorological Agency), all open data: a global wave model, surface wind and mean sea level pressure, a rain radar composite over the islands, tsunami status, ship track observations of sea surface temperature, salinity and current, and the coastal forecast for 48 coastal districts. On top of that a CMEMS wave grid on its own Japan window, and the ECMWF grid extended to cover Japanese waters.

The JMA publishes those bulletins in Japanese only - just the area names carry an English version. The wording is a fixed, limited vocabulary (wind directions, wave heights, a set list of weather terms), so it is translated term by term rather than by a translation service. Where the translation covers less than 60 percent of a sentence, the Japanese original is shown alongside it in square brackets so you can see it was only partly translated.

Those are TRACKOB reports: measurements logged by ships along their route and forwarded later, not a live feed. A delay of one to several days is normal for this source. Every point therefore shows its own observation time and how many hours ago it was taken - read that first, and use the model data for the current state.

Each model is only listed where we actually hold data for it. Many models are global, but the download is not: a window is cut out and stored, and outside that window there is nothing to show. Moving from Taiwanese into Japanese waters swaps one wave grid for another for that reason. An empty panel would suggest a calm sea; leaving the model out is the honest answer.

They show how far a source reaches. Switch on Asia to see the Blue Highway data box, the weather model window and the Japanese radar and wind coverage; switch on T.U s.w.a.n for the areas where the wave model has bathymetry tiles. Each box carries its name in the corner. Outside a box that source has no data, which is why panels change as you move.

It depends on the source, from every few minutes for radar and AIS to a few times a day for the big wave and current models. Panels show the time of the reading.

The source has not published a new run, or a fetch failed. Model runs arrive with hours of delay by their nature.

No. SeaData is a planning and awareness tool. It does not replace official nautical publications, charts or warnings, and the terms of use say so.

It differs per source and is named per row: MSL for most models, LAT or chart datum where a service publishes it that way. Mixing them without looking is a real risk.

Roughly the average height of the highest third of the waves. Individual waves can be considerably higher - a rule of thumb is that the highest wave in a few hours is about twice Hs.

True wind, from the models, at a standard height of ten metres. What you read on deck is apparent wind and will differ.

Metres, knots and degrees Celsius. Position format and speed unit can be set with the cog in the top bar.

UTC throughout, and it is labelled as such. On a ship that is the only sane choice.

Usually the connection. Reload the page with a hard refresh - hold shift while you reload. If the tiles stay empty, the base map service is unreachable; try another base map from the dropdown.

Either no model covers your position, or the fetch failed. Switch to another tab and back; if it stays empty at that position, there is genuinely nothing there.

Your browser is holding the old style sheet. A hard refresh - shift and reload - fixes it.

On a satellite link that is expected: the map fetches tiles and every panel fetches data. Switching off overlays you are not using helps.

Try a hard refresh first. If it persists, note which button and let us know - that is a fault, not a setting.

Check that SeaRain is switched on and that its settings point at the right region (Europe, Asia or World). Far offshore only World shows anything. Beyond that: there may simply be no rain.

AIS positions arrive in bursts and can arrive out of order. A jump of a few hundred metres is normal; a jump of miles suggests another ship is transmitting your MMSI.

Check the datum first - MSL and chart datum differ by metres. If the timing is off by more than half an hour at a station-backed harbour, let us know.

That page does not exist for your account. Some parts of the site are restricted, and they answer as if they are not there at all.

Yes, please. Note what you did, what you expected and what happened, and if you can, the time - that makes it findable in the logs.

No. Choosing not to show them again is stored on your account, so they stay away on every device you sign in from.

Your account details, your vessel's MMSI and last known position, and your sign-in history with IP address for ninety days. No sailing track, no browsing behaviour.

To spot accounts being shared and to investigate abuse. It is kept for ninety days and then deleted.

Only functional ones: staying signed in, your language and your unit settings. No advertising or tracking cookies.

No.

Ask us and you get what is held about you.

The cog in the top bar. The choice is remembered.

Also under the cog in the top bar, next to the position format.

The count next to Platforms under Map layer: how many AIS vessels are drawn. Zoomed out it adds zoom in for all ships, because then only your own fleet is shown.

It counts what is in view, so it changes as you pan and zoom and as ships move in and out of coverage.

The user guide behind the question mark in the top bar, and this search box you are using now.

Through the contact details on the site. Include your account email and the time something went wrong.

No. Everything is done with the mouse or by touch.

There is no print layout. A screenshot is the practical route.

Yes. Positions and readings update on their own; you do not need to reload.

Because even functional cookies have to be announced. There is nothing to opt out of beyond the necessary ones.

The site shows a maintenance notice and comes back by itself.

Yes, over https.

A switch under Map layer. It shows every fixed measuring station at sea - platforms, buoys and masts - with its latest wave, wind, current and visibility reading, from KNMI, Rijkswaterstaat, DMI, Copernicus Marine in-situ, Meetnet Vlaamse Banken, the Met Office, DWD and METAR from offshore platforms. Hover for the key values, click for every source with all its values. It refreshes every 10 minutes while it is on.

It was replaced by Platforms. The AIS layer is now switched with the AIS tab on the left: one click on, one click off. The count of vessels drawn stands next to Platforms.

Offshore platforms with a helideck publish aviation weather reports: METAR is the observation, TAF the forecast for the coming hours. The popup shows the values read from them (wind, visibility, weather) and the raw text as a pilot reads it. Visibility of 10 km or more is shown as 10 km or more, because that is all a METAR says.

Each source reports on its own rhythm, and every value keeps its own time. A buoy that stops reporting keeps showing its last value with its old time - so read the time next to the value before you use it.

It sits with the Tide stations flags bottom left and is on by default. It shows every station within 50 km of your position, whatever the flags say, and dims the flag row while it is on. Switch it off to choose countries with the flags again.

Your own map material. Upload points (TXT or CSV), shapefiles or KML on your profile, tab Areas; switch Areas on under Map layer to see them, with a list to hide each file. Points are drawn at true size, so zoom in to see them.

Typhoon draws the current CWA typhoon track, forecast cone and wind circle, with a banner saying how old the bulletin is; outside the season it is empty. IOC Tidal data shows the sea level stations of the IOC network (VLIZ/UNESCO).

Circles on convective cells above 40 dBZ - squalls, sudden gusts and poor visibility. Switch them on in the SeaRain settings (the cog in the SeaRain tab). Satellite in the same menu adds the hourly NOAA cloud image.

Our own precipitation layer. The SeaRain tab switches it on and off; the cog inside the tab sets the region (Europe, Asia or World), the quality (Fast, Normal or Sharp) and the extras. Switching on picks the region your vessel is in.

The eye button top right. One look before you open a tab: wave, wind, tide, a polar and current, each with the value now and a chart from 6 hours back to 24 hours ahead. The numbers are the consensus of all models; the chart shows the single best model. The polar shows where wind, wave and current come from against your heading and course over ground.

Harbour information from the World Port Index: every sea port in our areas that a vessel of 50 m or more can use, nearest first. Filter by area, LOA, draft and on Fuel, Water, Tugs, Ro-Ro or Medical. Something the index does not know is shown as a dash, never as zero or no - check the port itself before you rely on it.

It was removed. Tide ports in SeaHarbour still lists every tide port with the level now and the next high and low water, and clicking a port marker on the map opens that list on the port. For a full tide graph at your position, use SeaTide.

SWAN is a wave model run right at your position. It takes the swell of a coarser model onto the local depth and lists every quantity as a number: height, swell, periods, direction, wavelength, steepness and the motion near the seabed. It runs when the page loads and every 30 minutes; Recalculate forces a fresh run.

The server runs one SWAN calculation at a time for all users. If another run is busy, you see how many runs are ahead of you and the result follows by itself. If nothing comes free within 45 seconds the request stops and says so; try again shortly. Workability then uses the forecast model instead.

A table in SeaWave and SeaWind with the values every three hours of today, from the best-fitting model - the form in which they go into a Daily Progress Report.

A tab that answers what this vessel can do at this spot. You enter your vessel once; Workability then takes wave, wind and current for your position and shows per heading whether the motions and station keeping stay within your limits. It is a planning aid built on theory and forecast models, not a replacement for the judgement on board.

Every account type. Without signing in, the Workability tab shows the Demo vessel at the demo position, and nothing can be saved.

An example vessel with a drawing that every account gets once, so you see a full result straight away. It is your own copy: change it into your ship, rename it or delete it. It counts towards the vessels your account allows, and once deleted it does not come back.

On the Workability sub-tab pick a Moment (now up to +24 h) and press Calculate. The headline gives the best heading; the Waves, Wind and Current cards say why, each as Polar, Bars or Table. Green is below 0.8 of the limit, amber 0.8 to 1.0, red above.

With SWAN on, the moment now uses a SWAN run at your position; later moments always use the best-ranked wave model. With SWAN off, every moment uses the model. The line under the headline always says which source was used and why.

It answers whether you can work according to contract: per activity, per hour, up to 48 hours ahead. An hour counts only if every limit (Hs, wind, current, visibility) is met and it falls in a window at least as long as the minimum for that activity. The headline says how many activities are workable now and when the next window opens.

For waves and wind the average of the 3 best-fitting models for your position. For visibility the lowest of them, not the average - fog is local, and one model forecasting it makes the hour not workable. The models used are named under the headline.

The average of the total-current models for your position: CMEMS NWS, DMI DKSS and RWS DCSMv7. Where fewer than three cover you, FES2014 fills in, labelled tide only - it has the tide but not the wind-driven part.

They show the weather building up. Light orange: still workable, but within the margin of a limit. Dark orange: just over a limit, so not workable. The margin is set in Working limits as Near-limit margin, 10 by default, 0 switches it off.

Press Working limits (or Set limits in the orange bar) on the Contract tab. Per activity you set Hs, wind, current, visibility and the minimum window; add activities with + Add activity, go back with Reset to example values, and press Save and recalculate. The limits are saved per vessel: pick the vessel under Vessel first.

The selected vessel has no limits of its own yet, so Contract uses example values: Transit, Standby on Location, MBES and Crane. They are not your contract. Press Set limits, enter the limits of your vessel and contract, and save; the bar then disappears for that vessel.

The shortest workable spell that counts. A calm spell between two bad-weather periods that is shorter than this is shown striped amber and does not count as workable. Green stripes mean the window runs past the horizon, so its length is unknown.

The chance that Hs and wind stay within the limits, counted over ensemble members: ECMWF ENS (50 members, wind and waves, up to 72 h) and ICON-D2-EPS (20 members, wind, up to 48 h). It is information only: the colours and windows come from the top-3 average, the chance tells you how firm that answer is.

Because a full count of ensemble members is not a certainty. The count becomes a chance with the rule of Laplace - favourable plus one, divided by members plus two - so it runs from 1 to 99. Hours where current or visibility is already over its limit get 0.

It starts at the last three-hour mark (00, 03, 06 and so on, UTC), so there is always some history to compare with. Those hours are dimmed and count nowhere. The dashed now line marks the present and moves along every minute.

No forecast model covers that quantity at your position, so that limit is not applied - it says so under the headline. A single hour without data inside the horizon is grey: no model data, never silently approved.

That is the ceiling chosen for Contract: a visibility limit can be set up to 12000 m, and the chart draws visibility up to 12 km. A higher value saved earlier reads as 12000 m.

Under Vessel, inner tab 2D, block Your drawing: choose a Top view (DXF), a Side view (DXF) or both, max 5 MB each, and press Upload drawing. The lines replace the outline of the standard hull in the Top and Side view. Nothing is built from them.

A drawing is aligned to its aftmost and lowest line. If a stern platform or a thruster below the keel puts that off the transom or the baseline, enter the correction (Side: transom, Side: baseline, Top: transom) and watch the zero point move. Bow on the left and Top view mirrored fix a drawing that is the other way round.

No. Upload stability booklet (PDF) only stores it with your account, so we can look at it with you if you ask for support. Nothing is read or filled in from it: enter the values yourself under Config.

Not any more. The vessel is shown in two views, Top view and Side view, either as the outline of the standard hull or as your own uploaded drawing.

Under Vessel, inner tab Config, press Save. A profile is its name plus its loading condition: saving the same pair again overwrites it, a different loading condition is a separate profile.

The calculation point: heave and the vertical and transverse accelerations are worked out there. It does not have to be where work is done. Leave it empty and the centre of gravity is used. Wind and current always work about the centre of gravity.

Jack-ups, backhoe dredgers, semi-submersibles, catamarans and CTVs, and SWATH. The theory behind Workability is for monohulls; for these shapes it would give a number without meaning.

In Workability, tab External weather, add the address you send from under Receive by e-mail. Then mail the supplier's PDF to weather@wx.seadata.online from that address. Within a minute it is in the list. An address can belong to one account only.

The mail server sends it back with the reason, and the same reason is in Profile, Notifications. Mail is refused when it comes from an address that is not set, has no PDF, has more than 5 PDFs, has a PDF larger than 2 MB, or when the sender cannot be verified (SPF/DKIM). External weather shows a red Error until you open Notifications.

A forecast is only data for your vessel if its position lies within 50 km of it. From 50 to 100 km it is only plotted in External weather, with a warning; beyond 100 km, or without a position, it is read but not plotted. DPR and PDF always work.

DPR shows the supplier's own values at 06, 12, 18 and 06 UTC the next day, with a Copy button. PDF shows the pages of the original as images; the PDF itself is never opened in your browser.

Two recently added models. HARMONIE DINI is the 2 km wind model of DMI, covering north-west Europe including the North Sea. DWD EWAM is the European wave model of DWD at about 5.5 km. Both take their place in the ranking like every other model.

Ensembles: the same model run many times with slightly different starting conditions. ECMWF ENS has 50 members, ICON-D2-EPS 20. They are not in the ranking; they only feed the chance in Workability Contract.

HARMONIE, HARMONIE DINI, ICON-D2 and ICON-EU, and GFS outside Europe. Contract uses the lowest of the best three for your position.

A button in the bottom bar when you are not signed in. Enter an MMSI and you see that vessel as your own for half an hour, with the same data a customer gets. It only works for a vessel currently in our AIS reception; otherwise the page says so.

SeaData is built for positions at sea, not for towns. For a city forecast you want a normal weather service - this platform would only give you the nearest sea point.

Beyond what any model can honestly say. The radar here shows rain that exists right now, not rain in three weeks.

Outside the scope of a maritime data platform. Though a flat sea at sunrise comes close.

Not my department. Ask a colleague on watch - they have had more practice.

No, and it would be unfair to pretend otherwise. This is a written set of answers with a search box in front of it. The upside: it never invents anything.

It is built and maintained by a single developer. That is also why things change quickly.

Not something SeaData calculates. It depends on your hull, your engine and your loading - none of which the platform knows.

There is no route planner here. SeaData tells you what the conditions are; the route is yours to plan on a chart.

No. SeaData reads AIS and shows data; it does not connect to onboard systems.

No app - it runs in the browser. You can add it to your home screen and it will behave much like one.

Because it is data, about the sea. Some names do not need a story.

You can open it anywhere, but the models are marine. On a lake or a canal there is usually nothing to show.

Partly. The global models reach everywhere; the fine European models do not. Away from Europe you fall back on the coarse ones, and tide stations become sparse.

It happens. That is exactly why several models are shown side by side, and why measured values are marked differently from computed ones.

Deze handleiding beschrijft wat je op het scherm ziet, wat elke knop doet, en — het belangrijkste — hoe je moet lezen wat er staat. SeaData toont gegevens waarop vaar- en werkbeslissingen worden gebaseerd; dan is weten wáár een getal vandaan komt net zo belangrijk als het getal zelf. Knoppen en tabs staan hier precies zoals op het scherm: in het Engels.

1. Het hoofdscherm

De zeekaart vult het hele beeld. Alles eromheen zweeft erboven: de topbalk, de zijtabs links, Map layer rechtsboven, Tide stations linksonder, Overlay rechtsonder en de onderbalk.

De topbalk

Onderdeel	Wat het is
Vessels	Het actieve schip. Klik opent de vlootkiezer als je meerdere MMSI's hebt; alle schermen en de kaart volgen het schip dat je kiest. Het richtkruis ernaast brengt het schip terug in beeld (grijs zolang er geen positie bekend is).
Position	De AIS-positie van het actieve schip, in het gekozen formaat.
Speed / Heading	Snelheid over de grond in de gekozen eenheid (kn, km/h of m/s), en de koers.
Fix age	Hoe oud de positie is. Lees dit altijd mee.
Sea temp	Zeewatertemperatuur op je positie.
Hs / Wind / Current	De omstandigheden op je positie nu. Uit te zetten onder het tandwiel (Weather (Hs/Wind/Current)).
UTC	De klok. Alle tijden op dit platform zijn UTC.

Over «Fix age» — dit is geen detail

De kleur is een waarschuwing: groen onder 30 s, geel onder 5 min, oranje onder 15 min, rood daarboven.

Na 40 minuten wordt het schip niet meer getekend. Dat is opzet: een schip op een verouderde plek zetten suggereert zekerheid die er niet is. Staat er stale of no AIS, dan is er geen bruikbare positie — niet een positie die «wel ongeveer klopt».

Het getoonde getal is de som van twee leeftijden: hoe oud het laatste AIS-bericht is, én hoe oud de momentopname van de AIS-dienst zelf is. Valt de dienst stil, dan lijkt het bericht vers terwijl het dat niet is; door ze op te tellen zie je het echte risico.

Knoppen in de topbalk

? — deze handleiding, met bovenaan het zoekvak Ask about SeaData.
Klok — opent Data status: een ring per bron (zie hieronder).
Tandwiel — Language, Position format, Speed unit, de schakelaar Weather (Hs/Wind/Current) en AIS vessel (MMSI) om je schip in te stellen. De keuzes worden onthouden.
Zon / maan — wisselt het kleurthema.
Oog — opent Overview (zie hieronder).

De onderbalk

Cursorpositie links: de positie onder je muis.
Bullseye (alleen Fleet+ en Fleet admin) — kies een eigen plek op de kaart in plaats van het schip te volgen. Zolang hij aan staat is de knop geel en staat er op de kaart een gele waarschuwing ChartPos — manual position — not a vessel position. Alles geldt dan voor die plek, niet voor je schip.
Accountsoort, bijvoorbeeld Fleet admin.
Drie consensusringen: SeaWave consensus, SeaWind consensus en S.W.A.N consensus. Elke ring toont hoe goed de modellen voor jouw positie het eens zijn; de S.W.A.N-ring zet de golfhoogte van SWAN af tegen het gemiddelde van de andere modellen. De knop met het pijltje kiest het moment: now, +3h, +6h, +9h of +12h — vaste stappen, want de modellen publiceren maar om de paar uur.
About SeaData — wat SeaData doet en op welke bronnen het draait. De cookievoorkeuren staan onderaan dat paneel.
Profile en Log out als je bent ingelogd; Try it en Login als je dat niet bent.

Overview — de oog-knop

Eén blik voordat je een tab opent: WAVE, WIND, TIDE, een polar en CURRENT, elk met de waarde van nu en een grafiek van 6 uur terug tot 24 uur vooruit. De getallen zijn de consensus van alle modellen die je positie dekken; de grafiek toont het ene best passende model, want een gemiddelde van vormen vlakt de pieken weg. Tide zet het astronomische getij naast de werkelijke waterstand, Current de zuivere getijstroom naast de totale stroom. Next en Then zijn de eerstvolgende twee kenteringen van het getij in tijdsvolgorde; Slack is het eerstvolgende stroomstil.

De polar laat wind (blauw), golf (geel) en stroom (oranje) naar binnen wijzen — waar ze vandaan komen — en je koers (HDG, rood doorgetrokken) en koers over de grond (CoG, rood gestreept) naar buiten. Het verschil tussen die twee is je drift. De hoeken erboven zijn relatief aan je hartlijn: 000 recht vooruit, 090 dwars stuurboord.

Data status — de klok-knop

Een ring per databron, gegroepeerd als Wave, Wind + Warnings, Current, Tide, Observations en Radar. Een ring is één verversingscyclus: vol en groen vlak na een nieuwe run, en hij loopt leeg naar rood naarmate de cyclus opraakt. Rood betekent ook: ontbreekt of te laat. Loopt een model achter, dan zie je het hiér het eerst.

Recent bijgekomen: Met Office UKV, MET Norway MEPS, MEPS ensemble (30), DMI HARMONIE DINI, ICON-D2-EPS (20) en ECMWF ENS (50) onder Wind, DWD EWAM onder Wave, de stroommodellen DMI DKSS en RWS DCSMv7 onder Current, en Meetplatforms, METAR offshore en Copernicus in-situ onder Observations — de bronnen achter de kaartlaag Platforms.

2. De kaartbediening

2.1 Map layer (rechtsboven)

De keuzelijst kiest de basiskaart:

Kaart	Bron	Let op
OSM	OpenStreetMap	standaard
Voyager	CARTO	rustiger beeld
Ocean	Esri	zee-georiënteerd, tot zoom 13
Topo	OpenTopoMap	tot zoom 17

De SeaMarks-laag (OpenSeaMap: boeien, vaarwegen, lichten) ligt hier altijd overheen.

Zoom je verder in dan een kaart aankan (Ocean stopt bij 13), dan blijft het beeld leeg. Dat is de kaartlaag, geen storing.

Onder de keuzelijst staan schakelaars. Een gedimde vlag of een grijze knop betekent: die laag staat uit.

Schakelaar	Wat hij toont
EU model wind	Een vak per Europees windmodel (HARMONIE, DINI, ICON-D2, AROME, MEPS, ICON-EU/ECMWF), zodat je ziet welk windmodel waar geldt. MEPS heeft een scheve rand en staat er met zijn echte omtrek.
EU model wave	De gebieden van de Europese golfmodellen, per zeegebied. Staat nooit tegelijk aan met EU model wind: de een zet de ander uit.
Asia	De Aziatische databox (Taiwan / CWA) en de dekking van de Japanse radar en wind. Elke box draagt zijn naam in de hoek.
Typhoon	De actuele tyfoonbaan, verwachtingskegel en windcirkel van CWA, met een rode balk die zegt hoe oud het bericht is. Buiten het seizoen leeg.
T.U s.w.a.n	De gebieden waar het golfmodel SWAN dieptetegels heeft — waar SWAN kan rekenen.
IOC Tidal data	Zeeniveaustations van het IOC-netwerk (VLIZ/UNESCO).
Platforms	Vaste meetstations op zee met hun laatste meting — zie 2.2.
Areas	Je eigen kaartpunten en vormen, geüpload op je profiel (tab Areas: punten als TXT/CSV, SHP of KML). Er verschijnt een lijstje om elk bestand aan of uit te zetten. Punten staan op ware grootte, dus zoom in om ze te zien.

2.2 Platforms — metingen op zee

Platforms vervangt de oude AIS-knop in Map layer. Hij toont elk vast meetstation op zee met de laatste golf-, wind-, stroom- en zichtmeting, samengevoegd uit KNMI, Rijkswaterstaat, DMI, Copernicus Marine in-situ, Meetnet Vlaamse Banken, de Met Office, DWD-windstations (Alte Weser, Helgoland) en METAR/TAF van offshore platforms. Het ronde logo zegt wat het is: platform, buoy of mast / pile.

Aanwijzen geeft de naam en de kernwaarden (Hs, Wind, Current, Visibility) met hun tijd.
Klikken geeft elke bron op die plek met al zijn waarden; een METAR-station toont ook de ruwe METAR- en TAF-tekst.
De laag ververst elke 10 minuten zolang hij aan staat.

Hetzelfde platform meldt vaak aan meerdere diensten. Stations van dezelfde soort binnen 1 km worden één punt, met elke bron eronder. Elke waarde houdt zijn eigen tijd — lees die: een boei die stilvalt blijft zijn laatste waarde tonen.

2.3 Tide stations (linksonder)

Per land een vlag die de getij- en meetstations van dat land aan- of uitzet: NL, FR, UK, DK, NO, BE, SE, DE, EE, PL, LV, ES, PT, IT, TW, ID, JP. Alle vlaggen beginnen uit; een laag laadt pas bij de eerste keer aanzetten.

π 50km staat standaard aan: hij toont elk station binnen 50 km van je positie, wat de vlaggen ook zeggen. De vlaggenrij is dan gedimd. Zet hem uit om weer met de vlaggen te werken.

Vorm	Betekenis
Ruit	offshore-/meetstation zonder voorspelling
Driehoek	eiland
Cirkel	kuststation
Cyaan stip	meetboei

Klik op een station opent de details; aanwijzen geeft een korte samenvatting. Havens en hun getij staan in SeaHarbour.

2.4 Overlay (rechtsonder) — Waves en Wind

Waves — golfpijlen, kleur op significante golfhoogte Hs. Uitgebreid in SeaWave.
Wind — stroomlijnen, kleur op windsnelheid, met isobaren gelabeld in hPa. Uitgebreid in SeaWind.
De schuif onder elke legenda bepaalt hoeveel pijlen er getekend worden. De afstand wordt op je scherm gemeten, dus uitzoomen stapelt ze niet op.
Satellite — GEMETEN golfhoogte (stippen, van tien hoogtemeter-satellieten via Copernicus Marine) en wind (pijltjes, ASCAT via EUMETSAT) van de laatste 24 uur, in dezelfde kleuren als Waves en Wind. Het zijn sporen van echte metingen, geen veld: waar geen satelliet overkwam staat niets. Vol = 0–6 uur oud, half = 6–12 uur, licht = 12–24 uur. Een meting is 1,5 tot 3 uur oud als hij binnenkomt. Klik op een stip of pijl voor de waarde, de satelliet en de tijd.
Overlay klapt het blok weg zonder iets uit te zetten; Tide stations doet hetzelfde linksonder.

Golfhoogte-schaal (Hs): onder 0,5 m blauw · 0,5-1 m groen · 1-2 m geel · 2-3 m oranje · 3-4 m rood · boven 4 m donkerrood.

3. De zijtabs (links)

Tien tabs. Zeven openen een paneel; AIS, ForeCast en SeaRain zijn schakelaars die een laag op de kaart zetten. Alles geldt voor de positie van het actieve schip, of voor je bullseye-plek. Klik dezelfde tab nog eens of het kruisje om een paneel te sluiten.

SeaWave — golven

Drie tabs: Models (elk golfmodel dat je positie dekt, in de volgorde uit hoofdstuk 5), Online (TidesAtlas Marine) en S.W.A.N. Models heeft Graphics, Tables en DPR (de driehuurlijkse waarden van vandaag uit het best passende model, zoals een Daily Progress Report ze overneemt).

S.W.A.N draait het golfmodel SWAN precies op de positie van je schip en geeft elke grootheid als getal: golfhoogte en deining, alle perioden, gemiddelde en piekrichting met spreiding, golflengte en steilheid, en de orbitaalbeweging bij de bodem. Het rekent de deining van een grover model door naar de plaatselijke diepte; het is dus een puntberekening, geen kaartlaag. Hij rekent bij het laden van de pagina en daarna elke 30 minuten; Recalculate dwingt een verse run af. Een stoplicht zegt of de run compleet is.

SWAN rekent één run tegelijk. De server draait voor alle gebruikers samen één SWAN-run tegelijk. Is die van een ander bezig, dan staat er in oranje SWAN queue: waiting for computing power — N runs ahead of you, en het resultaat volgt vanzelf. Dat is een wachtrij, geen storing. Komt er binnen 45 s geen rekenkracht vrij, dan stopt de aanvraag en zegt dat; probeer het kort daarna opnieuw.

SeaCurrent — stroming

Now (getijstroom, totale stroom en reststroom met hun bron, een kompasroos, en een 3D-profiel tot 200 m waar het model dat levert), Prediction (per uur) en Graphics.

SeaWind — wind

Now, Charts, 7 days, DPR (wind, stoten en richting om de drie uur uit het best passende model), Models, Forecast (het KNMI-scheepvaartweerbericht) en Typhoon (cycloondata van CWA). Meerdere modellen naast elkaar, elk in een eigen kleur.

SeaTide — getij

Chart en Table. Twee groepen bronnen: de werkelijke waterstand (CMEMS NWS, Met Office NWS, IBI, MED) en het astronomische getij (EOT20, FES2022, DTU23).

Het verschil tussen die twee groepen is essentieel. Astronomisch is het getij zoals maan en zon het maken, zonder opzet door wind of luchtdruk. Actual is de modelwaterstand met opzet. Bij harde wind kunnen die meters uiteenlopen. Staan ze ver uit elkaar, dan is dat informatie: er zit opzet in.

SolarNav — zon, maan, ruimteweer

Space weather — Kp-index over drie dagen, F10.7-flux, zonnewind, Bz, de NOAA-schalen G/S/R, de GOES-zonnefoto en de impact op GNSS en Starlink.
Interference — GPSJam-kaart met GNSS-storing.
Sun & Moon — dageraad, zonsopkomst, middag, zonsondergang, schemering, daglengte en de maanfase met illuminatie, plus een tabel van zeven dagen.

Kp is een planetaire index — wereldwijd hetzelfde getal. De impact op jouw navigatie is dat niet: die wordt bijgesteld op de afstand tot de aurorale ovaal, en dus op je positie.

SeaHarbour — havens

Port info (opent eerst) — haveninformatie uit de World Port Index: elke zeehaven in onze werkgebieden waar een schip van 50 m of meer kan komen, dichtstbijzijnde eerst. Zoek op haven, land of UN/LOCODE, kies een gebied (Europe, Asia, Japan), vul je LOA en Draft in, en vink Fuel, Water, Tugs, Ro-Ro of Medical aan. Een haven toont de maximale scheepsmaat, dieptes, loodsdienst, sleepboten, faciliteiten, bevoorrading en reparatie.
Tide ports — alle getijhavens met de stand van nu en het eerstvolgende HW en LW. measured is een getijmeter, model is FES2022 en minder nauwkeurig in havens en rivieren. Hoogtes ten opzichte van MSL. Een havenmarker op de kaart opent deze lijst op die haven.

Onbekend is onbekend: een maat of ja/nee die de World Port Index niet kent staat er als streepje of staat er niet, nooit als 0 of «nee». Controleer de eigen informatie van de haven voordat je er een aankomst op plant.

AIS — andere schepen (schakelaar)

De tab AIS opent geen paneel meer: hij zet onze eigen AIS-laag op de kaart aan en uit. Uitgezoomd zie je alleen je eigen vloot; ingezoomd elk schip in beeld. De telling naast Platforms zegt hoeveel er getekend zijn, en uitgezoomd staat er zoom in for all ships bij.

Kleuren volgen het scheepstype. Een paarse ruit is een navigatiehulpmiddel (AtoN); alleen een omtrek betekent virtueel (bestaat niet fysiek), rood betekent uit positie.

Staat er AIS temporarily unavailable, dan ligt de bron stil — een lege kaart betekent dan niet dat er niemand vaart. AIS is onvolledig en vertraagd en is niet geschikt voor aanvaringsvermijding.

ForeCast — waarschuwingen per zeegebied (schakelaar)

ForeCast zet de gebieden van de nationale weerdiensten op de kaart. Klik op een vak voor het bericht van die dienst; de popup sluit vanzelf na 30 seconden.

Kleur	Dienst	Wat je krijgt
Oranje	KNMI	De districten van de Noordzee en het Nauw van Dover.
Donkerblauw	Météo-France	Vigilance: kleurcode per kustdepartement en Corsica, met de bulletintekst.
Rood	AEMET	Spaanse kustzones. Engelse vertaling boven, Spaans eronder; staat er een dekkingspercentage bij, dan is een deel niet vertaald.
Paars	IPMA	Portugese kustpunten, met de zeeverwachting van drie dagen: golfhoogte, richting, periode en zeewatertemperatuur.

De grenzen zijn bij benadering. Geen van deze diensten publiceert coördinaten bij zijn gebieden, IPMA uitgezonderd — daar zijn de vakken afgeleid van de kustpunten die zij zelf met positie geven. De vakken staan daarom gestippeld: ze wijzen een gebied aan, ze begrenzen het niet.

SeaRain — neerslag (schakelaar)

SeaRain vervangt de losse radarknoppen. Een klik op de tab zet onze eigen neerslaglaag aan en uit; het kleine tandwiel in de tab opent SeaRain settings zonder de laag te schakelen:

Region — Europe, Asia of World. Bij het aanzetten wordt de regio van je schip gekozen. World is een satellietschatting en de enige die op open oceaan iets laat zien; radar houdt een paar honderd km uit de kust op.
Quality — Fast (2 km), Normal (1,5 km) of Sharp (1 km). Scherper kost je browser meer geheugen.
Storm cells — cirkels op buienkernen boven 40 dBZ: rukwinden, windstoten, plots slecht zicht.
Satellite — het wolkenbeeld van NOAA, elk uur.

4. Workability

Wat kan dit schip op deze plek? Workability zit in elke accountsoort, en zonder in te loggen op het demoscherm. Negen subtabs, in de volgorde van gebruik: Workability (opent eerst), Contract, Transit, Reporting, External weather, Vessel Online, Vessel, Limits en How it works.

Workability is een planningshulp op basis van gesloten theorie en verwachtingsmodellen. Het vervangt het oordeel van de kapitein niet, en ook niet de eigen werkgrenzen van het schip of het contract zelf. De tab How it works zegt waar elk getal vandaan komt en waar je het niet moet vertrouwen.

Het Demo vessel

Elk account krijgt één keer een eigen Demo vessel: een voorbeeldschip met tekening, zodat je meteen een volledige uitkomst ziet. Het is van jou: je kunt het aanpassen tot je eigen schip, hernoemen of wissen. Het telt mee voor het aantal schepen dat je account mag hebben; gewist komt het niet terug. Op het demoscherm (niet ingelogd) ligt het op de demopositie in de Noordzee en kan er niets bewaard of geüpload worden.

4.1 Workability — het polair

Kies een Moment (now tot +24 h) en druk op Calculate. Golven, wind en stroom komen uit dezelfde bronnen die SeaWave, SeaWind en SeaCurrent voor die positie tonen. De kopregel geeft het antwoord (de beste koers); de kaarten Waves, Wind en Current zeggen waardoor, elk als Polar, Bars of Table.

Kleur per koers: workable onder 0,8 van de limiet, marginal 0,8-1,0, not workable boven 1,0, en een eigen merk voor roll resonance. De ring is de limiet.
SWAN on / off (rechts van Calculate): met SWAN aan rekent now met een SWAN-run op je positie; voor latere momenten, of met SWAN uit, met het golfmodel dat de ranglijst wint. De regel onder de kop zegt altijd welke, en waarom. Staat SWAN in de wachtrij, dan zie je Waiting for computing power.
What it calculated with noemt elke invoer: moment, golfbron, Hs/Tp/richting, windzee en deining, wind, stroom, het rekenpunt, windoppervlak, vorm van de zeegang en station keeping.
Confidence geeft de uitkomst een score (scheepsgegevens 50, omgeving 30, geldigheid van de theorie 20) en zegt wat hem beter maakt; eronder een polair van wind + stroom + golfdrift samen.

4.2 Contract — kunnen we werken volgens contract?

Per activiteit, per uur, tot 48 uur vooruit: blijft het weer binnen de contractlimieten, en lang genoeg? Druk op Calculate; de kopregel zegt hoeveel activiteiten nu werkbaar zijn en wanneer voor de rest het volgende venster opengaat.

Grootheid	Waarde waartegen getoetst wordt
Hs, wind	Het gemiddelde van de 3 best passende modellen voor deze positie (de ranglijst van SeaWave en SeaWind).
Stroom	Het gemiddelde van de modellen voor de totale stroom: CMEMS NWS, DMI DKSS en RWS DCSMv7. Zijn het er minder dan drie, dan vult FES2014 aan, met het label tide only.
Zicht	Het laagste model, niet het gemiddelde — mist is lokaal, en als één model mist voorspelt is het uur niet werkbaar. Getoond tot 12 km.

Een uur telt alleen als werkbaar als elke beoordeelde limiet gehaald wordt én het in een venster valt dat minstens zo lang is als het minimum van de activiteit. Een grootheid die geen model dekt is Not assessed, en dat staat in de regel onder de kop.

Timeline per activity — een blok per uur (UTC). Hij begint op het laatste drie-uursmoment (00, 03, 06 … UTC) vóór nu, zodat er altijd wat geschiedenis staat; die uren zijn gedimd en tellen nergens mee. De gestreepte now-lijn schuift elke minuut mee. Wijs een uur aan voor de waarden; klik op een activiteit voor zijn weer eronder.
Windows — per activiteit het volgende venster dat het minimum haalt, de lengte, wat het meest beperkt, hoeveel uren werkbaar zijn, en Chance now.
Weather against the limits — de lijn is het modelgemiddelde (zicht: het laagste), de band loopt van laagste tot hoogste model, de stippellijn is de limiet.

Kleur	Betekenis
Groen	werkbaar
Lichtoranje	werkbaar, maar binnen de marge van een limiet
Donkeroranje	net over een limiet (binnen de marge) — niet werkbaar
Rood	niet werkbaar, limiet overschreden
Oranje strepen	weer goed, maar het venster is korter dan het minimum
Groene strepen	het venster loopt voorbij de horizon; de lengte is onbekend
Grijs	geen modeldata — nooit stil goedgekeurd

Working limits (de knop met het tandwiel) opent de tabel Working limit for safe 24h vessel operations on site: per activiteit Hs, wind, stroom, zicht (tot 12000 m) en Min. window. De limieten horen per schip (het schip dat onder Vessel gekozen is; alle beladingstoestanden van een schip delen ze). Een schip zonder eigen limieten rekent met voorbeeldwaarden (Transit, Standby on Location, MBES, Crane) en een oranje balk Example limits zegt dat erbij: stel ze zelf in voor je erop vertrouwt. + Add activity, Reset to example values en Save and recalculate doen wat ze zeggen; zonder gekozen schip kan er niets bewaard worden. Near-limit margin (standaard 10 %, 0 = uit) bepaalt hoe dicht bij een limiet een uur oranje wordt.

De kans — alleen ter informatie

Het smalle cyaan blok onder elk uur is de kans dat Hs en wind binnen de limieten blijven, geteld over de leden van twee ensembles: ECMWF ENS (50 leden, wind en golven, tot 72 h) en ICON-D2-EPS (20 leden, wind, tot 48 h). Uren waarin stroom of zicht al over de limiet zijn krijgen 0. Van telling naar kans gaat met de regel van Laplace: (gunstig + 1) / (leden + 2), dus van 1 tot 99 % — een volle telling is geen zekerheid.

De kans verandert het go/no-go niet. De kleuren en vensters komen alleen uit het gemiddelde van de top 3. De kans zegt hoe stevig dat antwoord staat: een groen uur met een lage kans is een groen uur om in de gaten te houden.

4.3 Vessel — 2D en Config

Kies bovenaan het schip (Vessel); daaronder twee binnentabs.

Config — de scheepsgegevens in vier stappen: Required (profielnaam, scheepstype, Lpp, breedte, diepgang, werksnelheid) is genoeg om te beginnen; Stability booklet, Extended - motions en Station keeping (DP) maken het antwoord elk beter en de score hoger. Save bewaart op profielnaam plus beladingstoestand: zelfde paar, zelfde profiel. Elk veld heeft een what is this?.
Upload stability booklet (PDF) — alleen uploaden. Het booklet wordt bij je account bewaard, zodat we er samen naar kunnen kijken als je om ondersteuning vraagt. Het wordt niet automatisch gelezen en er wordt niets uit ingevuld: de waarden vul je zelf in.
2D — het schip in Top view en Side view, op dezelfde schaal. Kies wat een klik plaatst (Thruster, CoG, Working point); maten gaan vanaf 0,0,0 op spiegel, hartlijn en dek, zoals op een generalplan. Het werkpunt is het rekenpunt voor dompen en versnellingen; leeg betekent het zwaartepunt. What this layout can do toont wat de opstelling in langs-, dwars- en gierrichting kan na de worst case failure, zonder weer.

Je eigen tekening. Onder 2D kun je je eigen generalplan uploaden als DXF: Top view (DXF), Side view (DXF) of allebei, max 5 MB per stuk, en dan Upload drawing. De lijnen komen in Top en Side view in plaats van de omtrek van de standaardromp; er wordt niets uit gebouwd. De tekening wordt uitgelijnd op haar achterste en laagste lijn. Ligt die door een achterplatform of een thruster onder de kiel niet op de spiegel of de basislijn, vul dan de correctie in (Side: transom, Side: baseline, Top: transom) en kijk hoe het nulpunt verschuift. Bow on the left en Top view mirrored zetten een omgekeerde tekening recht.

De 2D-tab waarschuwt als een eenheid achter de spiegel, voor de boeg, naast het schip of boven de waterlijn staat — kijk die na voordat je de uitkomst van station keeping vertrouwt. Bewust niet aangeboden: jack-ups, backhoe-baggeraars, semi-submersibles, catamarans en SWATH; de theorie is voor eenrompsschepen.

4.4 Limits en How it works

Limits bevat wat voor dit werk nog acceptabel is: rol, stamp, dompen op het werkpunt, dwars- en verticale versnelling, een Hs-plafond, groen water en slamming op de boeg, en de benutting van de stuwkracht. Een Preset vult ze in (SeaData defaults, NORDFORSK intellectual work, NORDFORSK heavy manual work); daarna kun je elk getal aanpassen. Statistic kiest significante waarden of het verwachte maximum in 3 uur. How it works legt beide rekenketens uit en noemt elke bron met zijn status.

4.5 Vessel Online — wat het schip zelf doorgeeft

Alles hierboven rekent met modellen: een verwachting voor jouw positie. Vessel Online is de andere kant op — wat het schip zelf meldt, uit zijn eigen instrumenten. Een klein programma aan boord, SeaData.exe, luistert mee op het NMEA-netwerk van het schip en stuurt wat het hoort ongeveer elke zes seconden naar SeaData, over gewone https op poort 443. Alleen uitgaand: aan boord hoeft niets opengezet te worden, en er komt niets terug.

Je hebt de API-sleutel van je account nodig — daaraan ziet SeaData van wie dit schip is. Sleutel en programma staan allebei op het tabblad API in je account, en het schip moet in je vloot aangevinkt staan als Position via SeaData.exe. Zonder dat vinkje weigert de server de gegevens, en dat is met opzet: anders stuur je maandenlang data in voor een schip waarvan je alleen denkt dat het werkt.

Positie, vaart en koers — die gebruikt het platform overal: de kaart, de scheepskiezer, Transit. Ze liggen bovenop wal-AIS, want een schip weet zijn eigen positie beter dan een walstation.
Heading van de gyro, die in AIS vaak ontbreekt.
Rol, stamp en dompen — de grootste uitslag per as over het venster, de maat waarin je limieten staan.
Wind, waar en relatief, en luchtdruk, temperatuur, vochtigheid en dauwpunt van het weerstation aan boord.
Diepte zodra er een echolood aan hangt.

Het kan AIS vervangen waar AIS niet komt. Walstations horen je alleen dicht onder de kust, en de satellietbronnen zijn minuten tot uren oud. Een schip dat zijn eigen positie stuurt blijft in die gaten gewoon op de kaart staan — en dan elke zes seconden in plaats van elke paar minuten. Wal-AIS blijft de terugval: zet je het programma uit, dan valt het schip daar vanzelf op terug.

De tab laat zien of de verbinding leeft (een ring die met elke burst volloopt), wat er binnenkwam, de laatste zes uur als grafiek, het laatste bericht regel voor regel, en de bursts die geweigerd zijn met de reden erbij. Zes uur is het hele geheugen: wat ouder is valt eraf en er gaat niets de database in. Vandaag gebruikt het platform de positie; heading, beweging en weer worden bewaard om naar te kijken en rekenen nog nergens in mee.

De tijd in het bericht zelf ($GPZDA, satelliettijd) is waar elke leeftijd vanaf gerekend wordt — niet het moment waarop het pakketje toevallig binnenkwam. De tegel On the wire laat het verschil zien, en dat is de vertraging van de verbinding.

4.6 Reporting — het weerrapport dat je verstuurt

Contract geeft het antwoord op het scherm; Reporting maakt er een rapport van dat je kunt versturen. Je kiest een techniek uit de contracttabel van dit schip en krijgt het weer over de lopende dag en de dag erna: 48 uur, en het begint altijd op 00:00 UTC, niet op het uur waarop je toevallig kijkt. Drie uitvoeringen — op het scherm, als PDF en per e-mail — en alle drie komen ze uit dezelfde berekening, dus ze kúnnen niet uiteenlopen.

Het rapport noemt wat er over de limiet staat en met hoeveel procent, welke grootheid de beperking is, hoe lang het slechte weer nog duurt, wanneer er weer gewerkt kan worden en hoe ver de modellen uit elkaar liggen. Het rekent zelf niets: het middelen en toetsen blijft in Contract, het rapport vat die uitkomst samen en tekent hem.

De statusbalk — 48 uurvakjes per grootheid, met dezelfde kleuren als Contract, zodat een uur dat daar oranje is hier niet ineens rood is.
De meteogrammen — per grootheid elk model als eigen lijn, in de vaste kleur van dat model (dezelfde kleur als in SeaWave en SeaWind), met de limiet als rode lijn. Zicht krijgt bewust één lijn: mist is lokaal, en het contract rekent daar met het laagste model.
De limietladder — alles als percentage van zijn éigen limiet tegen één 100 %-lijn, zodat Hs in meters en zicht in meters naast elkaar te lezen zijn.
Betrouwbaarheid uit de ensembles (ECMWF ENS, 50 leden tot +72 u, en ICON-D2-EPS, 20 leden tot +48 u), per periode als high, moderate, low of very low. Is er geen ensemble voor deze plek, dan blijft het leeg — nooit een verzonnen percentage.
Valid at — het rapport hoeft niet over nu te gaan. Kies een 3-uurmoment in het venster (00:00, 03:00, 06:00 …) en het rapport geldt vanaf dat uur. De berekening is identiek; alleen de vensters, het percentage en "status now" tellen vanaf daar. Het rapport zegt het ook overal, en krijgt een eigen bestandsnaam.

De PDF is de papieren versie, niet een plaatje van het scherm: wit, met haarlijnen en een statusletter per uur, zodat een grijswaardenprinter de boodschap niet verliest. Mailen gaat naar een adres dat je zelf invult, met de PDF als bijlage; er zit een rem op van tien rapporten per account per uur, en vanaf het demoscherm kan het niet.

External weather hoort hierbij: het weerbericht dat je leverancier als PDF stuurt (DTN, StormGeo, Infoplaza). Je ziet wat wij eruit lezen en geeft het met Use in SeaData vrij; daarna staat het als extra lijn in de meteogrammen. Het verandert het go/no-go-oordeel nooit.

Uploaden of mailen. Upload de PDF, of stuur hem naar weather@wx.seadata.online vanaf een afzenderadres dat je in External weather hebt ingesteld. Een adres hoort bij één account.
De box: hoogstens 10 berichten (het oudste gaat eruit), elk 72 uur, hoogstens 2 MB per PDF — voor upload én mail.
Geweigerd (teruggestuurd door de mailserver) wordt mail van een onbekend adres, zonder PDF, met meer dan 5 PDF's, met een PDF groter dan 2 MB, of van een afzender die niet echt blijkt. De reden staat in Profile › Notifications; in External weather staat dan een rood Error.
Onbekende leverancier: de PDF wordt aangenomen en bij SeaData gemeld. Zodra het formaat gelezen kan worden, gebeurt dat vanzelf.
Afstand tot het schip: tot 50 km bruikbaar (Use in SeaData, Reporting); van 50 tot 100 km alleen geplot in External weather, met een waarschuwing; verder dan 100 km gelezen, maar niet geplot.
DPR toont 06, 12, 18 en 06 UTC de dag erna, precies uit de tabel van de leverancier; PDF toont de pagina's als plaatjes.

SeaData voert niets uit een PDF of mail uit: alleen de getallen uit de tabel worden gelezen, afgeschermd op de server. De PDF zelf komt nooit in je browser.

Een rapport is een momentopname van een verwachting. Verstuur je het, dan gaat de verwachting van dat moment mee; het loopt niet mee met een nieuwe modelrun. De uitgiftetijd staat er daarom in de kop bij.

5. De ranglijsten — welk model staat vooraan, en waarom

Dit is het hart van SeaData en het minst vanzelfsprekende deel. In SeaWind, SeaWave en SeaCurrent staan de modellen niet in een vaste volgorde: links staat het model dat het best bij jouw positie past, rechts het minst passende. De volgorde verandert dus terwijl je vaart.

De ordening wordt op de server bepaald, zodat geen enkel scherm een eigen volgorde kan verzinnen. Workability en Contract gebruiken dezelfde ranglijst.

De drie regels

Regel 1 — dekt het model je positie niet, dan valt het weg. Niets tonen is beter dan een grijs vlak dat zekerheid suggereert.
Regel 2 — sorteren op resolutie, fijnst links. Een model van 2 km ziet meer detail dan een van 13 km.
Regel 3 — straf voor randnabijheid. Aan de rand van zijn gebied wordt een model gestuurd door de randvoorwaarden die het van een grover model krijgt, niet door zijn eigen fysica. Een fijn model op 5 km van zijn rand is dus slechter dan een grover model dat er ruim binnen ligt.

Afstand tot de rand	Straf
minder dan 25 km	maal 3,0 (vol)
25 tot 50 km	maal 1,5 (half)
meer dan 50 km	maal 1,0 (geen)
wereldwijd model	maal 1,0

De score is resolutie in km maal straf; daarop wordt gesorteerd, laagste eerst.

Waarom 25 km? In de numerieke weersverwachting geldt als vuistregel acht tot tien rasterpunten voor de zone waarin de randvoorwaarden domineren; bij 0,025 graden is dat ongeveer 20 tot 25 km. De halve zone tot 50 km voorkomt dat een model van links naar rechts springt als je één zeemijl vaart.

Dit doet vanzelf wat «het model van het land zelf» zou doen: AROME ligt bij Brest diep in eigen gebied en bij Hoek van Holland erbuiten, HARMONIE precies andersom. Er is dus geen aparte landregel nodig.

De windmodellen

Model	Bron	Resolutie	Gebied
HARMONIE	KNMI	2,0 km	50-56 N, 1-8 O
HARMONIE DINI	DMI	2,0 km	47-64 N, -12-16 O
ICON-D2	DWD	2,2 km	47-58 N, -4-15 O
UKV	Met Office	2,0 km	45,5-62 N, 17 W-9 O (Britse eilanden, Kanaal)
MEPS	MET Norway	2,5 km	51-64 N, 0-16 O (Noordzee, Noorse kust)
AROME	Météo-France	2,5 km	41-51,5 N, -6-10 O
ICON-EU	DWD	7,0 km	30-66 N, -19-36 O
ECMWF IFS	ECMWF	9,0 km	EU + Azie + Japan
ECMWF AIFS	ECMWF	9,0 km	EU + Azie + Japan
Open-Meteo	Open-Meteo	11,0 km	wereldwijd
ICON global	DWD	13,0 km	30-70 N, -30-30 O
GFS	NOAA	13,0 km	wereldwijd
WRF 3km	CWA Taiwan	3,0 km	14-32,1 N, 105,3-140,9 O
CWA lokaal	CWA Taiwan	15,0 km	Taiwanese wateren
JMA GSM	JMA Japan	16,0 km	-20-60 N, 60-200 O

Het zicht (voor Contract) komt uit de windmodellen die het leveren: HARMONIE, HARMONIE DINI, ICON-D2, ICON-EU en GFS. De ensembles ECMWF ENS en ICON-D2-EPS staan niet in de ranglijst: die voeden alleen de kans in Contract.

De golfmodellen

Een rangorde van windmodellen zegt niets over golven — daarom een aparte lijst.

Model	Bron	Resolutie	Gebied
DMI WAM	DMI	1,1 km	53-60 N, 7-16 O
CMEMS Wave	CMEMS	1,5 km	NWS / Baltic
Met Office NWS	Met Office	1,5 km	46-62,7 N, -16-13 O
MFWAM	Météo-France	2,5 km	38-53 N, -8-12 O
IBI Wave	CMEMS	3,0 km	Iberië, Biskaje, Ierland
WW3 4km	MET Norway	4,0 km	48-65 N, -8-12 O
Med Wave	CMEMS	4,2 km	Middellandse Zee
DWD EWAM	DWD	5,5 km	30-66 N, -10,5-42 O
WW3 MEDITA	MeteoHub	11,0 km	30-46 N, -7-36,5 O
ECMWF IFS Wave	ECMWF	28,0 km	wereldwijd
CMEMS Asia Wave	CMEMS	9,0 km	20,7-28,9 N, 116,7-124,4 O
CMEMS Japan Wave	CMEMS	9,0 km	24-46 N, 122-150 O
Met Office Global	Met Office	13,0 km	wereldwijd
JMA Global Wave	JMA Japan	27,0 km	wereldwijd
CWA lokaal	CWA Taiwan	30,0 km	Taiwanese wateren
TidesAtlas Marine	TidesAtlas	25,0 km	wereldwijd, alleen onder Online

Hoe je de ranglijst leest

Bij elk model staat de reden van zijn plaats:

well inside its domain (180 km) — geen straf, volle waarde.
only 12 km from its domain edge — volle straf; dit model wordt hier gestuurd door zijn randvoorwaarden.
global model — wereldwijd, geen randprobleem, maar wel grof.

Praktisch: loopt het linker model ver uit de pas met de rest, kijk dan naar de reden. Staat het vlak bij zijn rand, neem het dan met een korrel zout — juist daarom staat de reden erbij.

6. Herkomst: gemeten, officieel of berekend

Elke waterstandswaarde draagt zijn herkomst, en de volgorde is niet willekeurig:

Badge	Betekenis
measured	een echte meting van een meetstation of boei
official	de voorspelling van de hydrografische dienst zelf (Rijkswaterstaat, DMI, SHOM, Environment Agency …)
computed	SeaData's eigen harmonische som uit een getijmodel

Officiële bronnen gaan vóór eigen berekening. Geeft de dienst het uit, dan toont SeaData dat — niet zijn eigen som. Grijs betekent: geen betrouwbare officiële bron voor dit station.

Verschillen tussen modellen worden getoond, niet weggepoetst. Lopen modellen uiteen, dan is de verwachting onzeker. Dat mag je zien.

7. Accounts en schepen

Een account volgt één of meer schepen op MMSI. Welk soort je hebt bepaalt hoeveel plekken je krijgt en hoe vrij je daarin kunt wisselen. Workability zit in elk soort.

Soort	Schepen	Wisselen	Eigen kaartpositie	Viewers
Single	1	direct — weghalen en opnieuw invullen	nee	nee
Fleet standard	5	plek 7 dagen op slot	nee	nee
Fleet+	3	onbeperkt	ja	ja
Fleet admin	5	onbeperkt	ja	ja

Viewers (Fleet+ en Fleet admin): alleen-kijken-logins voor bemanning, kantoor of klant, te maken onder Profile › Viewers.

Een schip is nergens te bewerken. Er is geen wijzigknop: je haalt een schip weg met het kruisje en vult daarna een ander MMSI in. Bij Single, Fleet+ en Fleet admin kan dat meteen; bij Fleet standard blijft de plek eerst zeven dagen op slot.

Zolang er geen schip staat

Zonder schip is er geen AIS-positie om de gegevens op te betrekken. SeaData valt dan terug op een vaste plek op de Noordzee. Alles wat je ziet — getij, golven, wind, stroming — geldt dan voor díé plek en niet voor jou. Zodra je een MMSI invult volgt het beeld je schip weer.

De wachttijd bij Fleet standard

Haal je een schip weg, dan blijft die plek zeven dagen bezet. Je ziet dat op je accountpagina staan, met de datum waarop hij weer vrijkomt. Zonder die wachttijd zou het aantal plekken niets voorstellen: je zou een schip kunnen weghalen en meteen een ander toevoegen, en zo onbeperkt wisselen. Bij de andere soorten geldt de wachttijd niet.

Eigen plek op de kaart

Fleet+ en Fleet admin hebben de bullseye-knop in de onderbalk waarmee je een willekeurige plek op de kaart kiest in plaats van je schip te volgen (zie hoofdstuk 1). Bij de andere soorten volgt de data het actieve schip.

Zonder account

Try it in de onderbalk opent een pagina waar je een MMSI invult en dat schip een half uur als je eigen schip ziet. Dat lukt alleen voor een schip dat nu in onze AIS-ontvangst zit; anders zegt de pagina dat. Zonder in te loggen toont de tab Workability het Demo vessel op de demopositie.

Registratie

Elk account wordt met de hand beoordeeld en vrijgegeven. Voor informatie of een demo-account mail je naar het adres in de topbalk (admin@seadata.online). Je krijgt bericht zodra het account is goedgekeurd; daarna kun je inloggen.

8. Voorbehoud

SeaData is ondersteunende informatie, geen navigatiemiddel.

Controleer gegevens altijd tegen officiële bronnen: zeekaarten, getijtafels en berichten aan zeevarenden.
Astronomische getijden bevatten geen opzet door wind of luchtdruk.
AIS is onvolledig en vertraagd en is niet geschikt voor aanvaringsvermijding.
Workability en Contract zijn schattingen op basis van modellen; de beslissing om te werken blijft bij het schip.
SeaData aanvaardt geen aansprakelijkheid voor het gebruik van deze gegevens.

De voorwaarden staan op Voorwaarden; de volledige bronvermelding met houder, licentie en voorgeschreven vermelding staat op Bronvermelding.

9. Snel iets oplossen

Wat je ziet	Waarschijnlijke oorzaak
Kaart hapert bij zoomen	Zet Waves en Wind uit onder Overlay, of schuif hun schuif naar links; dat zijn de zwaarste lagen.
Leeg vlak bij inzoomen	De basiskaart heeft een zoomgrens (Ocean tot 13, Topo tot 17).
Weinig AIS-schepen	Uitgezoomd zie je alleen je eigen vloot — zoom in voor alle schepen in beeld.
Positie blijft leeg	Geen AIS-ontvangst voor dat MMSI, of de positie is te oud.
Schip verdwenen van de kaart	Positie ouder dan 40 minuten; bewust niet getekend.
Getij wijkt af van de tafel	Astronomisch model zonder opzet — vergelijk met de actual-lijn.
Geen regen op de kaart	Zet SeaRain aan en kijk de regio na in de instellingen; radar reikt niet tot open oceaan — probeer World.
Geen getijstations	π 50km staat aan en er ligt er geen binnen 50 km; zet hem uit en gebruik de vlaggen.
SWAN blijft wachten	Er draait al een andere SWAN-run; hij rekent er één tegelijk. Het resultaat volgt vanzelf, of probeer het zo opnieuw.
Contract zegt Not assessed	Geen model dekt die grootheid op deze positie; die limiet wordt niet toegepast.
Tekening staat verkeerd	Vul onder 2D de correctie voor spiegel of basislijn in, of vink Bow on the left / Top view mirrored aan.

Datastatus

…

vershalverwegeverlopen

Elke ring is één verversingscyclus: vol en groen net na een verversing, leeglopend naar rood naarmate de cyclus verstrijkt. Rood betekent ook dat de data ontbreekt of te oud is.

—

SeaWave consensus

—

SeaWind consensus

—

S.W.A.N consensus

—

Over SeaData Uitproberen Inloggen

BETA

SeaData — jouw wateren, jouw data.

Waarom SeaData:

Alleen officiële bronnen. Getij en waterstand van de hydrografische diensten zelf — Rijkswaterstaat, DMI, MET Norway, SMHI, BSH, Environment Agency en SHOM. Meet SeaData het niet en geeft een dienst het niet uit, dan staat het er niet.
Modellen van naam. Stroming en waterstand uit Copernicus Marine (CMEMS) en het Met Office NWS-model, golven uit WAM en WAVEWATCH III, wind uit ECMWF, ICON en HARMONIE, en getij uit de wetenschappelijke modellen EOT20, FES2022 en DTU23.
Gemeten waar het kan. Boeien en meetpalen van de Noordzee tot de Oostzee — Meetnet Vlaamse Banken, KNMI, CANDHIS en de nationale meetnetten — zodat je naast de verwachting ook ziet wat er werkelijk staat.
Je ziet wáár het vandaan komt. Elke waarde draagt zijn herkomst: gemeten, officieel of berekend. Verschillen tussen modellen worden getoond, niet weggepoetst — want die zeggen iets over de zekerheid van het beeld.
Alles op één kaart. Getij, stroom, golven, wind, regenradar en AIS in één beeld aan boord — geen losse sites en apps meer naast elkaar.

Maak een account aan en vaar met je eigen data.

Let op: SeaData is nog in beta. Verwachtingen en metingen kunnen onvolledig of onjuist zijn. Controleer ze altijd tegen de officiele berichtgeving voor de scheepvaart.

Waiting for data…

Wave

Wind

Tide

Vessel

Current

Waiting for tide data…

Actual water level

Astronomical tide

Per source

Waiting for wave data…

Models, ranked

Checked against satellites

Hs · all models

Components

Daily progress report

Waiting for current data…

Current rose

3D profile · now

Speed

Direction

Waiting for wind data…

Models, ranked

Wind rose

Wind · all models

Selected model

Pressure · all models

Temperature and precipitation

Daily progress report

Model

What it calculated with

On the best heading

Confidence

All together — motions and station keeping

Limits of the theory

Timeline per activity

Windows

Weather against the limits

Route and waypoints

Route options

Passage against the Contract limits — set speed vs speed now

Weather along the route

Speed, tide and ETA

What this means

Position and heading

Motion — measured, not modelled

Weather on board

Last 6 hours

Last burst received

Refused bursts

Your drawing

Top view

Side view

Positions, all measured from 0,0,0

Centre of gravity

Other loading condition

Working point

Loading — the two draft marks

Thrusters

Other points

What this layout can do

Step 1 · Required

Step 2 · Stability booklet

Step 3 · Extended - motions

Step 4 · Station keeping (DP)

1What this screen answers

2Two chains under one polar

3From five fields to a whole ship

4Chain A - the motions

5Chain B - station keeping

6The calculation point

7The top view, and the two sets of axes

8Height, and the acceleration you feel sideways

9The hull outline and your own drawing

10Significant or RMS - the factor two that bites

11The three plots, three views each

12Where the weather comes from

13External weather from your supplier

14The confidence score

15Where not to trust it