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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🌊 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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Time (UTC)	DMI WAM	CMEMS Wave	Met Office NWS	MFWAM	IBI Wave	WW3 4km	Med Wave	WW3 MEDITA	ECMWF IFS	CWA lokaal	CMEMS Asia	MET Office ASIA
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 °
Loading…

One source: the model that fits this position best. Empty rows before the model run are shown as —, not as zero.

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.

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

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

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

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

Type	Date	Time (UTC)	Height
Select a port.

⚠

Supporting information — not a navigation aid. Always verify data against official sources: nautical charts, tide tables and notices to mariners. Tides are astronomical and exclude surge from wind or air pressure. AIS is incomplete and delayed and is not suitable for collision avoidance. SeaData accepts no liability for the use of this data. Terms

User guide

Ask about SeaData

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

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 bottom of the screen. Everything else follows that position: open a side tab on the left for waves, current, wind or tide.

Yes. Without an account the map shows a fixed demo position and no vessel data. With an account the data follows your ship.

Use the Login link in the top bar. After signing in you land on your profile; from there 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.

Dutch and English. Switch with the language links in the top bar; the choice is remembered.

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.

Bottom right, open Radar and switch on a country. Each national service covers its own waters, so switch on the ones near you.

Two possible reasons: there is no precipitation, or no national radar reaches that far. Radar coverage stops well before mid-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 at the bottom, 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.

The bottom bar shows it, and it follows your cursor over the map. The cog in the top bar sets the format - degrees, minutes or decimal.

That depends on your account type. Where it is available there is a bullseye button at the bottom to drop your own point instead of following the ship.

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.

Each tab opens a panel with charts and tables for your position: SeaWave, SeaCurrent, SeaWind, SeaTide, SolarNav, SeaHarbour, AIS and ForeCast.

The clock button at the bottom left opens Data status: one ring per source, grouped by kind (waves, wind, current, tide, observations, 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.

Nearby harbours with their tidal times and levels, so you can judge when you can enter.

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.

An external traffic map, useful for a wider look around than the vessels on our own map.

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.

In your profile, under Vessels. 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.

The bottom bar shows the age of the last fix. Positions older than about 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 bottom of the map. 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.

SeaWave and SeaWind show a consensus ring above the charts. It reads the models for your position and shows how well they agree at fixed steps - now, +3, +6, +9 and +12 hours - not on a sliding scale, because the models only publish every few hours and anything in between would fake a precision that is not there. The best-fitting model is named separately: that is the one whose grid sits closest to your position.

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.

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 a country is switched on under Radar, and that it is a country near you. 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.

How many vessels are currently in view on the map.

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.

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.

This guide describes what you see on screen, what every button does, and — most importantly — how to read what is shown. SeaData presents data that passage decisions are based on; knowing where a figure comes from matters as much as the figure itself.

1. The main screen

The chart fills the whole view. Everything else floats above it: the top bar, the panels on the left, the chart menu on the right and the legends.

Item	What it is
Vessel / fleet	The active vessel. Click to open the fleet picker if you have several MMSIs.
Position	The AIS position of the active vessel, in the chosen format (dd / dm / dms).
SOG	Speed over ground, in the chosen unit (kn / km/h / m/s).
Age	How old the position is. Always read this too.
Tidal status	Arrow and text: rising, falling, or the next extreme with its time.
Weather	Current sea conditions at your position.

About «Age» — this is not a detail

The colour is a warning: green under 30 s, yellow under 5 min, orange under 15 min, red beyond that.

Beyond the configured limit the vessel is no longer drawn. That is deliberate: placing a vessel at a stale position implies a certainty that is not there. If it says stale or no AIS, there is no usable position — not a position that is «roughly right».

The figure shown is the sum of two ages: how old the last AIS message is, and how old the AIS service snapshot itself is. If the service stalls, the message looks fresh when it is not; adding them shows the real risk.

Buttons in the bar

Fleet — choose the active vessel; all panels and the chart follow.
Cog — units and formats: position, speed, course.
Clock — opens the data status panel: how old the latest run is per source. If a model is lagging, this is where you see it first.
About — what SeaData does and which sources it runs on.
Cookies — set your cookie preferences again.
Bullseye, bottom left — centres the chart on the active vessel; click the chart afterwards to pull data for another spot.

2. The chart menu (right)

2.1 Chart — the base map

Map	Source	Note
OSM	OpenStreetMap	default
Voyager	CARTO	calmer rendering
Dark	CARTO	dark mode
Ocean	Esri	sea-oriented, up to zoom 13
Topo	OpenTopoMap	up to zoom 17

The SeaMarks layer (OpenSeaMap: buoys, fairways, lights) always sits on top of these.

Zoom in further than a map supports (Ocean stops at 13) and the view stays empty. That is the map layer, not a fault.

2.2 Models — Wind and Waves

Wind — streamlines with an arrow head, coloured by wind speed, including isobars (labelled in hPa about every 300 km). In full in SeaWind.
Waves — wave arrows, coloured by significant wave height Hs. In full in SeaWave.
Wave Models — focus mode: switches every other layer off and shows only the wave model domains as coloured areas, zoomed out to about 500 km. One look tells you which model applies where. Switching it off restores the normal view.

Wave height scale (Hs): below 0.5 m blue · 0.5-1 m green · 1-2 m yellow · 2-3 m orange · 3-4 m red · above 4 m dark red.

2.3 Tide stations — the flags

One flag button per country to switch its tide stations on or off: NL, BE, DE, DK, NO, SE, UK, FR, PL, LV, EE. The shapes mean something:

Shape	Meaning
Diamond	offshore or measuring station without prediction
Triangle	island
Circle	coastal station
Cyan dot	measuring buoy

Clicking a station opens its tidal curve; hovering gives a short summary. Ports and their tides are in SeaHarbour.

2.4 Radar — precipitation

Four independent radar layers: UK (Met Office), DMI (Denmark), KNMI (Netherlands) and FR (Météo-France). Each covers its own area and they partly overlap. If a radar stays empty it does not cover your area — try another.

2.5 AIS

Shows other vessels: those within 25 km of each of your own vessels — not whatever happens to be in view. Zooming out therefore does not make the picture heavier.

Drag the chart to an area where none of your vessels are and you will see no AIS targets there. That means we are not looking here, not nobody is sailing here.

Colours follow the vessel type. A purple diamond is an aid to navigation (AtoN); an outline only means virtual (it does not physically exist), and red means off position.

AIS is incomplete and delayed and is not suitable for collision avoidance.

2.6 Notice to Mariners

The KNMI district boundaries, dotted and labelled «approximate». Dotted on purpose: a solid line on a chart reads as an established boundary, and these are not.

3. The panels (left)

Six panels, each with the sub-tabs Chart and Table — same data, different form. Everything applies to the position of the active vessel, or to the spot you click on the chart.

SeaTidal — tide

Four to five sources side by side: EOT20, FES2022 and DTU23 (astronomical tide models), plus CMEMS and Met Office NWS (modelled sea level).

The difference between those two groups is essential. Astronomical is the tide as sun and moon make it, without surge from wind or air pressure. Actual is the modelled sea level including surge. In strong winds they can differ by metres. When they are far apart, that is information: there is surge.

SeaWave — waves

Wave height (Hs), period (Tp/Tm) and direction per model. The model order follows the ranking in chapter 4.

A third tab, S.W.A.N, runs the SWAN wave model right at your vessel's position and lists every quantity as a number: wave height and swell, all the periods, mean and peak direction with spread, wavelength and steepness, and the orbital motion near the seabed. It refines the swell from a coarser model onto the local depth, so it is a point calculation rather than a map layer. It updates when a vessel is selected and refreshes every 30 minutes; the Recalculate button forces a fresh run, with a timer showing how long it takes (usually ten to twenty seconds). The bottom bar carries a third consensus ring, S.W.A.N consensus, comparing SWAN's own wave height against the average of the other models.

SeaWind — wind

Wind speed, gusts, direction, pressure, precipitation and temperature; several models side by side, each in its own colour.

SeaCurrent — current

Tidal current and residual current, with a 3D profile down to 200 m where the model provides it. Deeper than that it falls back on point computation.

SeaHarbour — ports

Ports within a radius of your position, with their tides. Click a port for the full curve of that station.

SolarNav — sun, moon, space weather

Space weather — Kp index over three days, F10.7 flux, solar wind, Bz, the NOAA G/S/R scales, the GOES solar image and the impact on GNSS and Starlink.
Interference — GPSJam map showing GNSS interference.
Sun & Moon — dawn, sunrise, noon, sunset, dusk, day length and the moon phase with illumination, plus a seven-day table.

Kp is a planetary index — the same figure worldwide. The impact on your navigation is not: it is adjusted for the distance to the auroral oval, and thus for your position.

ForeCast — warning areas by sea region

ForeCast is not a panel but a switch: it turns the areas of the national weather services on and off. Click an area for that service's bulletin; the popup closes by itself after 30 seconds.

Colour	Service	What you get
Orange	KNMI	North Sea and Dover Strait.
Dark blue	Météo-France	Vigilance: colour level per coastal department and Corsica, with the bulletin text.
Red	AEMET	Spanish coastal zones. English translation on top, Spanish below; a coverage percentage means part of it is untranslated.
Purple	IPMA	Portuguese coastal points, with the three-day sea forecast: wave height, direction, period and sea temperature.

The boundaries are approximate. None of these services publishes coordinates with its areas, except IPMA — there the areas are derived from the coastal points they publish with a position. That is why the areas are dashed: they point at a region, they do not bound it.

4. The rankings — which model leads, and why

This is the heart of SeaData and the least obvious part. In SeaWind, SeaWave and SeaCurrent the models are not in a fixed order: the model on the left fits your position best, the one on the right least. The order therefore changes as you sail.

The ordering is decided on the server, so no panel can invent an order of its own.

The three rules

Rule 1 — if a model does not cover your position, it is dropped. Showing nothing is better than a grey area that implies certainty.
Rule 2 — sort by resolution, finest on the left. A 2 km model sees more detail than a 13 km one.
Rule 3 — a penalty for being near the edge. Near the edge of its domain a model is driven by the boundary conditions it receives from a coarser model, not by its own physics. So a fine model 5 km from its edge is worse than a coarser model well inside its own domain.

Distance to the edge	Penalty
less than 25 km	times 3.0 (full)
25 to 50 km	times 1.5 (half)
more than 50 km	times 1.0 (none)
global model	times 1.0

The score is resolution in km times penalty, and that is what is sorted on, lowest first.

Why 25 km? In numerical weather prediction the rule of thumb is eight to ten grid points for the zone where the boundary conditions dominate; at 0.025 degrees that is roughly 20 to 25 km. The half zone out to 50 km keeps a model from jumping from left to right when you sail a single nautical mile.

This does by itself what «the country's own model» would do: AROME sits deep inside its domain off Brest and outside it off Hoek van Holland, and HARMONIE the other way round. No separate country rule is needed.

The wind models

Model	Source	Resolution	Domain
HARMONIE	KNMI	2,0 km	50-56 N, 1-8 E
ICON-D2	DWD	2,2 km	47-58 N, -4-15 E
AROME	Météo-France	2,5 km	43-51,5 N, -6-3 E
ICON-EU	DWD	7,0 km	47-62 N, -12-15 E
ECMWF IFS	ECMWF	9,0 km	47-66 N, -12-31 E
ECMWF AIFS	ECMWF	9,0 km	47-66 N, -12-31 E
Open-Meteo	Open-Meteo	11,0 km	global
ICON global	DWD	13,0 km	30-70 N, -30-30 E
GFS	NOAA	13,0 km	global

The wave models

A ranking of wind models says nothing about waves — hence a separate list.

Model	Source	Resolution	Domain
DMI WAM	DMI	1,1 km	53-60 N, 7-16 E
CMEMS Wave	CMEMS	1,5 km	NWS / Baltic
Met Office NWS	Met Office	1,5 km	46-62,7 N, -16-13 E
MFWAM	Météo-France	2,5 km	38-53 N, -8-12 E
WW3 4km	MET Norway	4,0 km	48-65 N, -8-12 E
Open-Meteo Wave	Open-Meteo	25,0 km	global
TidesAtlas Marine	TidesAtlas	25,0 km	global
ECMWF IFS Wave	ECMWF	28,0 km	global

How to read the ranking

Each model states the reason for its place:

well inside its domain (180 km) — no penalty, full value.
only 12 km from its domain edge — full penalty; here this model is driven by its boundary conditions.
global model — worldwide, no edge problem, but coarse.

In practice: if the leftmost model differs markedly from the rest, read its reason. If it sits close to its edge, take it with a pinch of salt — which is exactly why the reason is there.

5. Provenance: measured, official or computed

Every sea level figure carries its origin, and the order is not arbitrary:

Badge	Meaning
measured	a real measurement from a station or buoy
official	the prediction of the hydrographic service itself (Rijkswaterstaat, DMI, SHOM, Environment Agency …)
computed	SeaData's own harmonic sum from a tide model

Official sources take precedence over our own computation. If the service publishes it, SeaData shows that — not its own sum. Grey means there is no reliable official source for that station.

Differences between models are shown, not smoothed away. If models disagree, the forecast is uncertain. You are entitled to see that.

6. Accounts and vessels

An account follows one or more vessels by MMSI. The type of account determines how many slots you get and how freely you can change them.

Type	Vessels	Changing	Own chart position
Single	1	straight away — remove and enter another	no
Fleet standard	5	slot on hold for 7 days	no
Fleet+	3	unlimited	no
Fleet admin	3	unlimited	yes

A vessel cannot be edited. There is no edit button: you remove a vessel with the cross and then enter another MMSI. On Single and Fleet+ you can do that straight away; on Fleet standard the slot stays on hold for seven days first.

While no vessel is set

Without a vessel there is no AIS position to base the data on. SeaData then falls back to a fixed spot in the North Sea. Everything you see — tide, waves, wind, current — applies to that spot and not to you. Enter an MMSI and the view follows your vessel again.

The hold period on Fleet standard

Remove a vessel and that slot stays reserved for seven days. Your account page shows this, with the date it becomes available again. Without that hold the number of slots would mean nothing: you could remove a vessel and add another straight away, changing as often as you like. Fleet+ and Fleet admin have no hold period — there, changing freely is the difference.

Own position on the chart

Only Fleet admin has the bullseye button at the bottom that lets you pick any spot on the chart instead of following your vessel. On the other types the data follows the active vessel.

Registration

Every request is reviewed by hand. You get a confirmation that it arrived and a message once it has been approved; you can sign in after that. If you sign in earlier, the screen tells you the request has not been approved yet.

7. Disclaimer

SeaData is supporting information, not a navigation aid.

Always check against official sources: charts, tide tables and notices to mariners.
Astronomical tides contain no surge from wind or air pressure.
AIS is incomplete and delayed and is not suitable for collision avoidance.
SeaData accepts no liability for the use of this data.

The terms are at Terms; the full attribution with holder, licence and required credit is at Attribution.

8. Quick fixes

What you see	Likely cause
Chart stutters when zooming	Switch Wind and Waves off; those are the heaviest layers.
Empty area when zooming in	The base map has a zoom limit (Ocean to 13, Topo to 17).
No AIS vessels	You are looking at an area without one of your own vessels — AIS follows the fleet (25 km).
Position stays empty	No AIS reception for that MMSI, or the position is too old.
Vessel gone from the chart	Position older than the limit; deliberately not drawn.
Tide differs from the tables	Astronomical model without surge — compare with the actual line.
Radar empty	That radar does not cover your area; try another.

1. The main screen

About «Age» — this is not a detail

Buttons in the bar

2. The chart menu (right)

2.1 Chart — the base map

2.2 Models — Wind and Waves

2.3 Tide stations — the flags

2.4 Radar — precipitation

2.5 AIS

2.6 Notice to Mariners

3. The panels (left)

SeaTidal — tide

SeaWave — waves

SeaWind — wind

SeaCurrent — current

SeaHarbour — ports

SolarNav — sun, moon, space weather

ForeCast — warning areas by sea region

4. The rankings — which model leads, and why

The three rules

The wind models

The wave models

How to read the ranking

5. Provenance: measured, official or computed

6. Accounts and vessels

While no vessel is set

The hold period on Fleet standard

Own position on the chart

Registration

7. Disclaimer

8. Quick fixes

SeaData — your waters, your data.