The Lerwick-registered creel boat Majestic went down off Shetland on 21 January after water got into the engine room.
Two crew members of the 52ft vessel, brothers from Shetland, escaped into a life-raft shortly after discovering the flooded engine compartment, while five nautical miles off the island of Yell. They were later picked up by another fishing boat that was in the area.
But investigators have now revealed that after the crew abandoned ship it drifted and then hit the seabed just two metres from the pipeline.
The report by the Marine Accidents Investigation Branch found that the bilge alarms, in the unattended wheelhouse, had been going unheard for up to an hour as water filled the boat.
Both the skipper and his brother were working on deck when the alarm sounded.
However, it was not until the skipper went to the wheelhouse around 10am that he heard the alarm.
The men sent a mayday call and abandoned ship into a life-raft. The boat remained upright for four and a half hours but drifted and then foundered a few feet away from BP’s Orka Vow pipeline, 100 metres below the surface.
Investigators came to the conclusion that the cause of the engine room flood was probably a failure within a seawater system or valve.
A number of safety recommendations have been made to the skipper of the boat.
The report stated: “This accident indicates that relevant guidance and the lessons from similar accidents were not being sufficiently heeded.
“Majestic’s wheelhouse was left unattended for a prolonged period and the crew were not practised in reacting to a flood on board.
“They did not wear personal flotation devices while working on deck and did not don lifejackets when abandoning the vessel.
“Had the skipper and the crewman been alerted as soon as the bilge alarms sounded, the likelihood of them being able to enter the engine room to turn on the motor- driven bilge pump, and to identify and resolve the source of the water ingress would have increased significantly.”