AIS navigational status codes, all sixteen

Every Class A position report carries a four-bit navigational status field. Four bits gives sixteen values, all of them defined, and they are the most misread numbers in AIS. Speed and position come from a GNSS receiver. Navigational status comes from a menu on the bridge that someone has to remember to change.

The sixteen codes

Code	Meaning	What it actually tells you
0	Under way using engine	The default and by far the most common. Also what you see on ships that never touch the setting.
1	At anchor	The vessel reports itself anchored. Cross-check against speed over ground and whether it is swinging.
2	Not under command	NUC. Through some exceptional circumstance the ship cannot manoeuvre as required — usually a machinery or steering failure. A serious declaration.
3	Restricted manoeuvrability	RAM. The nature of the work restricts the ability to manoeuvre: dredging, cable laying, replenishment, towing operations that severely restrict the tow.
4	Constrained by draught	A power-driven vessel that can only navigate within a narrow channel because of its draught relative to available depth. Frequently over-claimed by ships that simply want right of way.
5	Moored	Alongside a berth or made fast to a buoy. Distinct from anchored.
6	Aground	The hull is on the bottom. Rare, and when genuine it is an incident.
7	Engaged in fishing	Fishing with gear that restricts manoeuvrability. Not “is a fishing boat” — a trawler steaming to the grounds should report 0, not 7.
8	Under way sailing	Under sail alone, with engines off. A yacht motor-sailing should report 0.
9	Reserved for future use — high-speed craft (HSC)	Reserved. Some regional guidance uses it for dangerous-goods HSC carriage.
10	Reserved for future use — wing-in-ground (WIG) craft	Reserved, with regional dangerous-goods use as above.
11	Towing astern	A tug with the tow on a wire behind it. Added in the 2012 revision of the standard, and only defined for regional inland-waterway use in some interpretations.
12	Pushing ahead or towing alongside	A pusher tug made up to a barge, or a tug on the hip. Same 2012 vintage as 11.
13	Reserved for future use	Unassigned.
14	AIS-SART, MOB or EPIRB active	An emergency locating device is transmitting. This is a distress indication.
15	Undefined	The “not available” default. This is what a transponder sends when nobody has set anything.

Codes 11 and 12 replaced values previously reserved, so older equipment and older archived data may not use them consistently. If you are comparing tracks across several years, treat 11 and 12 as recent additions rather than a stable series.

How we handle it here

Our ingest normalises status 15 to null and every page prints “Not reported” for it, because “Undefined” dressed up as a value invites a reader to over-interpret it. Any other code we show as-is, with the standard’s wording. We do not infer status from behaviour and we never overwrite what the ship transmitted.

We do use status for one derived thing: a small set of codes — at anchor, moored, aground — flags a vessel as not making way, which is useful for filtering. That derivation is stated where it appears.

Where it goes wrong

The failure modes are consistent and worth internalising:

• Code 0 on a ship that is stopped. Extremely common. The ship anchored, nobody changed the setting, and speed over ground reads 0.1 knots while the status still says “under way using engine”. Believe the speed.
• Code 1 or 5 on a ship that is moving. The mirror image: a ship departs and the status stays on “moored” for hours.
• Code 4 as a courtesy claim. “Constrained by draught” has a precise meaning under the collision regulations and carries privileges. It is claimed more often than it is true.
• Code 7 as an identity. Some fishing vessels leave status 7 set permanently, including in port. It is meant to describe the current activity.
• Code 2 in error. “Not under command” occasionally appears from a mis-keyed menu rather than a genuine casualty. If you see it, look for corroboration — a sudden drift track, a change in heading with no course change — before treating it as an incident.

The general rule: navigational status is testimony, and position, speed and course are measurement. Where they disagree, the measurement is usually right. Where they agree, you have learned something.

Reading status alongside the rest of the report

The field becomes much more informative in combination:

• Status 1 with speed under 0.5 kn and a slowly rotating heading is a ship swinging round its anchor. That is a coherent picture.
• Status 5 with a position 400 m off any quay is not.
• Status 7 with speed of 2 to 4 kn and an erratic course is what active trawling looks like. Status 7 at 11 kn on a straight line is a boat going somewhere.
• Status 3 near a known works area, with a matching ship type, is credible restricted manoeuvrability.

None of that is an official interpretation, and none of it should be used operationally — see the not-for-navigation notice on every map view on this site. It is a way of reading the data honestly, which is the whole point of the exercise.