What does “under way using engine” mean?

Status 0: the ship is not anchored, moored or aground and is using its engines. “Under way” does not mean moving: a ship drifting with its engines ready is also under way.

What does navigational status 15 mean?

Undefined: the default value when nobody has set a status. It is common on equipment where the crew never configured the field.

Why does a ship show “at anchor” while moving?

Because the status is set by hand and the crew did not change it when the ship weighed anchor. Trust the measured speed and position over the status.

AIS navigational status codes explained

Updated Sep 28, 2026 · 3 min read

In short

The navigational status is a field in a ship’s AIS position report that says what the ship is doing: under way using its engine, at anchor, moored, fishing, restricted in its ability to manoeuvre, and so on. It is a number from 0 to 15, defined in Recommendation ITU-R M.1371. Unlike position and speed, it is set by hand by the crew, so it is often out of date: a ship can report “at anchor” while steaming at 12 knots.

The sixteen codes

The status field is four bits long, so it can only hold the values 0 to 15.

AIS navigational status (ITU-R M.1371)
Code	Status	What it means
0	Under way using engine	Moving, or ready to move, under its own power.
1	At anchor	Anchored, typically waiting for a berth, cargo or orders.
2	Not under command	Cannot manoeuvre as required, for example after an engine or steering failure.
3	Restricted manoeuvrability	Limited by its work: dredging, laying cable, supplying offshore, some towing.
4	Constrained by her draught	Can only use a narrow deep channel because of its draught.
5	Moored	Tied up alongside a berth or buoy.
6	Aground	On the bottom.
7	Engaged in fishing	Fishing with gear that restricts manoeuvrability.
8	Under way sailing	Moving under sail.
9	Reserved (HSC)	Reserved for future use by high-speed craft.
10	Reserved (WIG)	Reserved for future use by wing-in-ground craft.
11	Power-driven vessel towing astern	Regional use.
12	Power-driven vessel pushing ahead or towing alongside	Regional use.
13	Reserved for future use
14	AIS-SART, MOB-AIS or EPIRB-AIS (active)	Sent by an activated rescue transmitter, not by a ship.
15	Undefined	The default: nobody has set a status.

Codes 1 to 8 follow the categories of the International Regulations for Preventing Collisions at Sea (COLREGs), which also decide the lights and shapes a ship shows. IMO’s guidelines suggest changing the AIS status whenever the lights or shapes change.

Who sets it, and why it is often wrong

Position, speed, course and heading come straight from the ship’s sensors. The navigational status does not: IMO resolution A.1106(29) says it “has to be manually entered by the officer of the watch and changed as necessary”. When nobody changes it, it stays at whatever was last set, or at 15 if it was never set.

That is why a tracking service should never read the status alone. Voydar shows the reported status next to the measured speed, and decides whether a ship is moving from its speed and position, not from the status field.

Navigational status of ships heard in the last hour

Live from Voydar

Every ship Voydar received a position from in the last hour, grouped by the status its crew has set. 38,290 ships heard in the last hour

Code	Status	Ships	Share
—	No status sent	12,759	33%
0	Under way using engine	10,818	28%
5	Moored	9,736	25%
1	At anchor	1,748	5%
15	Undefined	1,198	3%
7	Engaged in fishing	563	1%
3	Restricted manoeuvrability	409	1%
8	Under way sailing	404	1%
12	Power-driven vessel pushing ahead or towing alongside	362	1%
11	Power-driven vessel towing astern	83	0%
2	Not under command	55	0%
9	Reserved (HSC)	49	0%
4	Constrained by her draught	47	0%
13	Reserved for future use	24	0%
6	Aground	21	0%
10	Reserved (WIG)	10	0%
14	AIS-SART, MOB-AIS or EPIRB-AIS (active)	4	0%

Voydar count of distinct MMSIs whose latest AIS position is less than one hour old, by the navigational status field of that position. “No status sent” is mostly Class B equipment, whose position reports have no status field. Coverage follows Voydar’s receivers and feeds, so this is a sample of world shipping, not all of it. As of Oct 1, 2026, 21:16 UTC

Ships with no status at all

Class B transponders, used by yachts, small fishing boats and workboats, send a different position message that has no navigational status field. On Voydar those ships show no status rather than “undefined”. In waters with many leisure boats they can make up a large share of what a receiver hears, which the live table above shows.

Reading a status on a ship page

At anchor with speed near zero is the usual picture of a ship waiting off a port. Many anchored ships together can mean congestion.
Moored with a recent position inside a port area usually means a port call in progress; see how Voydar detects port calls.
Not under command or aground are worth a second look, especially if the speed has dropped to zero away from a port. They can also be left over from a drill.
Undefined (15) on a large ship is a data-quality flag: the crew has not set the field.

Questions and answers

What does “under way using engine” mean?: Status 0: the ship is not anchored, moored or aground and is using its engines. “Under way” does not mean moving: a ship drifting with its engines ready is also under way.
What does navigational status 15 mean?: Undefined: the default value when nobody has set a status. It is common on equipment where the crew never configured the field.
Why does a ship show “at anchor” while moving?: Because the status is set by hand and the crew did not change it when the ship weighed anchor. Trust the measured speed and position over the status.

Look up a ship

Search any vessel by name, IMO number or MMSI for its free Voydar profile: live position, identity history, ownership, inspections and sanctions.

Sources

Primary sources for the facts in this guide. Figures labelled as Voydar data come from Voydar’s own records, with their method stated next to them.

Published Sep 28, 2026 · For information only. Not for navigation, and not a substitute for the official sources cited.