AIS navigational status
AIS navigational status 4: Constrained by her draught
Its depth limits it to a narrow channel. What status 4 means, what speed and track should go with it, and how often it is simply wrong.
What status 4 means
A power-driven vessel that, because of its draught relative to the available depth and width of water, is severely restricted in its ability to deviate from its course.
What should go with it
Normal passage speed along a deep-water route or channel.
Navigational status is entered by hand on the bridge; speed, course and position come from a satellite receiver. Read the status as testimony and the rest as measurement. Where they agree you have learned something. Where they disagree, the measurement is usually right.
How it goes wrong
The status carries privileges under the collision regulations, and it is claimed more often than it is true. On its own it is a claim, not a measurement.
The matching lights and shapes
The AIS status mirrors a state defined in the International Regulations for Preventing Collisions at Sea (COLREGs), which also say what the vessel should display:
Rule 28 — a cylinder by day; three all-round red lights in a vertical line at night.
Summary for orientation only. The COLREGs text is the authority; this site is not a navigation reference.
All sixteen codes
| Code | Meaning |
|---|---|
| 0 | Under way using engine |
| 1 | At anchor |
| 2 | Not under command |
| 3 | Restricted manoeuvrability |
| 4 | Constrained by her draught |
| 5 | Moored |
| 6 | Aground |
| 7 | Engaged in fishing |
| 8 | Under way sailing |
| 9 | Reserved for future amendment (HSC) |
| 10 | Reserved for future amendment (WIG) |
| 11 | Power-driven vessel towing astern |
| 12 | Power-driven vessel pushing ahead or towing alongside |
| 13 | Reserved for future use |
| 14 | AIS-SART, MOB-AIS or EPIRB-AIS active |
| 15 | Undefined (default) |
For the field as a whole — and how this site handles it — read AIS navigational status codes, all sixteen.