Confidential Human Factors
Incident Reporting Programme
The Charity
Aviation
Maritime
M2304
Initial Report
Our reporter recounts an encounter between their large vessel in the North Atlantic and two small autonomous surface vessels, also known as Maritime Autonomous Surface Ships (MASS). Although both vessels were detected on AIS and radar from 7 nautical miles away, visual detection was difficult, even in mild sea conditions.
The first vessel was directly ahead of the ship and the closest point of approach (CPA) was approximately 0.5 nautical miles.
About 45 minutes later, a second, slightly smaller uncrewed vessel was encountered. It was initially assessed to be drifting, with a CPA of 0.2 nautical miles on the starboard side, and the ship altered course to port to increase the CPA to 0.4 to 0.5 nautical miles. However, as the ship approached, the uncrewed vessel increased speed to about 5 knots and started crossing the ship’s bow at close range requiring an immediate alteration of course to result in passing at a safe distance.
CHIRP Comment
There are an increasing number of uncrewed vessels operating at sea, and the IMO is developing a MASS Code for adoption as early as 2025. In the interim, existing regulations such as SOLAS and the Collison Regulations apply, and vessels must have a designated human ‘master’ regardless of the level of autonomy (see table). This person, if not on board, will work from a remote location and remains obliged to maintain a proper lookout by all available means (ColReg rule 5). Presently this includes transmitting its location on AIS and monitoring VHF – even uncrewed vessels should respond to radio calls!
Table 1: The IMO’s 4 degrees of autonomy
| Degree | Definition |
| 1 | Some processes automated but there are seafarers on board |
| 2 | Remotely controlled ship with seafarers on board |
| 3 | Remotely controlled ship without seafarers on board |
| 4 | Fully autonomous ship |
Vessels encountering autonomous vessels should treat them as they would any other vessel and apply the ColRegs accordingly. This includes passing at a safe distance, and not making the mistake of approaching closer because of their small size.
Mariners encountering uncrewed surface vessels (USVs) during commercial and recreational navigation are encouraged to identify and record the AIS information and report any deviations from the Colregs to CHIRP Maritime (reports@chirp.co.uk) Such reports will contribute valuable insights into the operational challenges and safety considerations associated with autonomous vessels, supporting the development of best practices and regulatory measures for safe navigation around USVs. By sharing these experiences, mariners will play a critical role in enhancing awareness and ensuring that the transition to greater autonomy at sea prioritises safety for all.
Key Issues relating to this report
Situational Awareness- Autonomous vessels can be very small – keep a good lookout and refer to AIS and Notices to Mariners to identify if they are operating or being trialled near your area of operations.
Communications- It might feel counterintuitive or unreasonable but do contact the vessel by VHF if in doubt regarding their intentions.