Why is the distance by sea longer than the straight line?

A ship has to go round the land. From Rotterdam to Singapore the straight line is about 5,700 nautical miles, and the shortest way by sea, through the Suez Canal, about 8,400.

When will she arrive?

The rail does not say. Preview route works out how long the rest of the route would take at her speed now, which is not a forecast. Her ETA, in her voyage above the rail, is what her crew typed in, and her card says when it has passed and may not be updated.

Why is there no distance for my ship?

Shiptrail needs to know both her ports and to hear her on the map now, and both ports must lie within 30 nautical miles of the shipping lanes. Without those there is no rail, and her page gives the straight line alone.

Where does the route come from?

From Eurostat's SeaRoute network of shipping lanes, under the EUPL-1.2 licence. About credits it with the other sources.

How far is a ship from port? Distance to go by sea

The short answer

Open a ship's card on the live map, or her page, and look at her voyage. When Shiptrail knows the port she left and the port she is bound for, a thin rail runs between the two with her mark on it, and a line such as 2,847 nm to go by sea. That is how far she still has to sail along the shortest sea route, worked out from where she was last heard.

Under it, a second line gives the length of the whole route and says she may sail another way. It is a guide to the distance, not her plan: the ships themselves choose their way, and Shiptrail hears them through receivers, most of them on land.

How to see how far a ship has to go

Find her on the mapType her name, MMSI, IMO number or call sign into the search box on the live map and pick her from the list. How to track a ship says more about finding one.
Look at her voyageHer card, and the Voyage card on her page, say where she left from, where she is bound and when her crew expects to arrive. Her page also gives the distance to that port in a straight line.
Read the railUnder her voyage, the rail shows the route from one port to the other, her place on it, how far she has to go by sea and how long the whole route is. On her page it takes a moment to appear, while your browser works the route out.
Preview the routeWhile she is still on her way, Preview route, under the rail, opens her route on the live map: the shortest way from where she is to the port, drawn over the lanes, with her ship moving along it as she is heard. Its panel gives the distance left by sea, the time that would take at her speed now, which is not an ETA, her own ETA as she broadcast it, and a canal on the way, or one she is too big for with its limit. Back to live returns to her card.
Choose your unitsDistances are in nautical miles. Units, in the map's Settings, gives them in kilometres (Metric) or miles (Imperial) instead.

Why not a straight line

A ship cannot sail over land. From Rotterdam to Singapore, a straight line is about 5,700 nautical miles and runs across Europe and Asia. The shortest way by sea, through the Suez Canal, is about 8,400. The straight line under To on her page is still worth having as a quick sense of how far away the port is, and the rail is how far she has to sail.

How the route is worked out

The route follows Eurostat's SeaRoute network, a web of the lanes ships use, built on a shipping lane network from the Oak Ridge National Laboratory and on European coastal lines from AIS. Your browser fetches it when it first needs it, finds the shortest way along its lines between her two ports, and then works out where she is on that way.

Where a canal is the shorter way, the route takes it: the Suez, Panama, Kiel and Corinth canals are on the network. A ship too long or too wide for a canal is sent the long way round. The Kiel Canal takes ships up to 235 m long and 32.5 m wide, so from IJmuiden to Rostock a ship that fits goes about 350 nautical miles through it, and a larger one about 640, round the top of Denmark. The Panama Canal takes up to 370.33 m by 51.25 m, and the Corinth Canal up to 22.5 m wide. The Suez Canal's limits pair a ship's width with her draught, which Shiptrail does not compare, so no ship is kept out of it.

Reading the rail

To go by seaHer distance along the route from her place to the port.
AboutHer distance to go and the length of the whole route say about when her two ports together lie more than 10 nautical miles from the nearest lanes, and her distance to go says it when she is more than 3 nautical miles off the route.
Off the routeWhen she is more than 25 nautical miles from it, the rail says how far, and the distance is worked out again from where she is now.
Close, and in portWithin 5 nautical miles of the port the rail says she is close to it, and once she lies in port it says so, with no distance left to give.
No timeThe rail gives no arrival time. Preview route gives the time the rest would take at her speed now, which is not a forecast. Her ETA, in her voyage above the rail, is the one her crew typed in, and her card says when it has passed and may not be updated.

There is no rail when Shiptrail does not know both ports, when they are the same port, when she is not on the map, or when either port is more than 30 nautical miles from the nearest lane, as some river and estuary ports are. Her page then keeps the straight line alone.

Where it can be wrong

She may sail another wayWeather, traffic lanes, a pilot station, a call on the way or her company's own route can all take her off the shortest one.
Her ports can be out of dateHer crew types in where she is bound for each voyage, and can forget. Where she left from is Shiptrail's own reading, from where she last lay stopped. How ports are counted says how a ship is placed in a port.
Her place is her last reportA ship is placed where receivers last heard her, and her page can be a few minutes old. The card on the live map is the freshest.
Not for navigationThe network is simplified and the figure is a guide for following a ship, never for planning a passage.

Questions people ask

How far is a ship from port?: Open her card on the live map or her page. When Shiptrail knows the port she left and the port she is bound for, the rail under her voyage says how far she has to go by the shortest sea route.
Why is the distance by sea longer than the straight line?: A ship has to go round the land. From Rotterdam to Singapore the straight line is about 5,700 nautical miles, and the shortest way by sea, through the Suez Canal, about 8,400.
When will she arrive?: The rail does not say. Preview route works out how long the rest of the route would take at her speed now, which is not a forecast. Her ETA, in her voyage above the rail, is what her crew typed in, and her card says when it has passed and may not be updated.
Why is there no distance for my ship?: Shiptrail needs to know both her ports and to hear her on the map now, and both ports must lie within 30 nautical miles of the shipping lanes. Without those there is no rail, and her page gives the straight line alone.
Where does the route come from?: From Eurostat's SeaRoute network of shipping lanes, under the EUPL-1.2 licence. About credits it with the other sources.

Data sources and credits

Ship positions

AISStream, which relays what volunteer receivers hear.
Norwegian waters: Data delivered by BarentsWatch, collected by the Norwegian Coastal Administration, under the Norwegian Licence for Open Government Data (NLOD) 2.0.
Finnish waters: Source: Fintraffic / digitraffic.fi, license CC 4.0 BY.

The rest

Sea routes: the shortest path over Eurostat's SeaRoute maritime network (EUPL-1.2), which builds on a shipping lane network courtesy of Oak Ridge National Laboratory, U.S. Dept. of Energy, with European coastal lines from AIS. Not for navigation.
The map, the weather, the charts and the type are credited on About.

Distance to port by sea