.jpg)
The short answer
A port's page counts three things: the ships in port now, the ships on their way there, and the ships that left it in the last 48 hours. Each count is a list you can open, and a ship is on at most one of a port's lists. If you came here from a port's page wondering where a number comes from, this is it.
The counts are of the ships Shiptrail hears, through receivers on land, so they are only as complete as the coverage is. The last two sections say what that does to a port's numbers.
The three lists
In port is the simplest. A ship counts as in port once she is under half a knot within 20 km of the port. That takes in a ship alongside a berth and one waiting at anchor for a berth, and Shiptrail does not tell the two apart.
En route is for ships heading there. A ship is en route to a port when her crew has named it as her destination and her arrival time is still ahead, or she gave none. Once the time has passed she drops off the list, because crews often leave the old destination in after arriving. A ship that has gone out of range stays on the list for up to 14 days after she was last heard, as long as she was last heard more than 40 km from the port, because a ship crossing an ocean can be unheard for days and is still on her way.
Departed is for ships that have left. A ship counts as departed when she lay stopped near a port for at least 10 minutes and then got under way at over 3 knots, and she stays on that port's list for 48 hours. A stop of under 10 minutes is no call. A ship that sails out of range stays for the 48 hours, with when she was last heard, unless she was last heard lying in a port.
What gets counted
A ship is on one list at most. If she is in port at a port, she is not also heading there or gone from it, and a ship heading back to the port she left is en route to it, not departed from it. A ship with no name or no position is on no list at all.
Any ship with a transponder counts, so a marina full of sailing boats counts like a container terminal, which is why a yacht harbour such as Antibes can rank among the busiest. A big harbour can be split, too: Botlek, inside Rotterdam's harbour, has its own code and its own count.
Why some ports look busier
The map hears ships through receivers on land, many run by volunteers. Europe and North America have the most, so their ports can look busier than equally busy ports elsewhere. A quiet port may just be a port with few receivers near it.
So read a port's numbers as the ships the receivers heard, which is a fair picture where receivers are many and a thin one where they are few. Positions are not for navigation.
Where to look next
Ports lists the 15 ports with the most ships in port right now, and a port with at least 5 ships across its three lists is busy enough to get an anchor on the live map from zoom 6. Honolulu is a good page to open to see the three lists. Step 6 of How to track a ship says how to find any port, and Why a ship disappears says what happens to a ship that goes out of range.
Questions people ask
- Why does a port's count differ from the map's?
- The map's numbers are as of the last minute, and a port's page can be kept for up to 10 minutes, so the two can differ by that. They never differ by how they count: the page, the map and the busiest ports list all use the same rule.
- What makes a port busy?
- At least 5 ships across its three lists. The sitemap lists such ports and the map marks them with an anchor, and Ports lists the 15 with the most ships in port.