Accidents

Royal Navy Submarine, Trawler Karen

A Royal Navy submarine snagged the fishing gear of the trawler Karen. The trawler was dragged backwards at about 7 knots and suffered structural damage.

On 15 April 2015, a submerged Royal Navy submarine snagged the fishing gear of the UK registered trawler  Karen, 15 miles south-east of Ardglass, Northern Ireland. Karen had been trawling for prawns on a westerly  heading at 2.8 knots when its fishing gear was snagged and it was dragged backwards at about 7 knots.  Karen’s crew managed to release both winch brakes, freeing the trawl warps; the starboard warp ran out  completely but the port warp became fouled on the winch drum, causing the vessel to heel heavily to port  and its stern to be pulled underwater. Karen broke free from the submarine when the port warp parted;  there was structural damage to the vessel but it returned to Ardglass safely under its own power. Evidence  of the collision on board the submarine was either not observed or misinterpreted.

The nature of sub-surface operations requires the use of sonar technology to detect collision hazards.  Detection in this way is reliant on noise emanating from contacts. In this instance the fishing trawler was  detected but misidentified as a merchant vessel rather than a fishing vessel because the submarine’s sonar  operators did not detect or report hearing trawl noise. Given the number of vessels operating in the area, it  is almost certain that the noise levels being generated would have been extremely high, with noise from one  vessel masking the noise from another. Such a situation would make it very difficult for the sonar operators  to methodically identify and analyse each contact, in particular to identify discrete acoustic classification  clues such as trawl noise. As a result the trawler was assessed to be that of a small merchant vessel and  the command team’s perception would have been that no risk of collision could exist between a submarine  at safe depth and a merchant vessel.

Review concluded that the submarine was operating near to the limit of its capability. Given that all the  submarine’s systems were reported to be functioning properly, it was apparent that the submarine’s limit  of capability had, in reality, been exceeded, with its sonar and command teams becoming cognitively  overloaded, leading to degraded situational awareness and poor decision-making.

In conclusion, the Maritime Accident Investigation Board (MAIB) report stated, “The collision happened  because the submarine’s command team believed Karen to be a merchant ship, so they did not perceive  any risk of collision or need for avoiding action.”

This incident highlights the importance of the resolution Data Property, specifically with regards to resolving  a trawler and a merchant vessel. It also highlights the importance of the integrity, specifically with regards  to the information provided from the sonar team to the command team.

Links 

https://www.gov.uk/maib-reports/collision-between-the-stern-trawler-karen-and-a-dived-royalnavy-  submarine
(accessed 29 November 2017).