Duncan Matheson is likely to have fallen overboard from the tenders as he moved to secure it alongside the fishing vessel Fram of Shieldaig in Loch Torridon, it said.
The vessel’s skipper was unable to recover him on-board after the incident at about 8am on 7 August last year, according to the report from the Marine Accident Investigation Branch (MAIB).
It was the fifth fatal person overboard accident investigated by the MAIB since October 2015 involving vessels based in remote Scottish locations - in each case no life jacket was worn.
The report said it is likely the 62-year-old struck his head as he entered the water, either losing consciousness as a result of the band of through the effects of cold-water immersion.
The skipper, 51, attempted to recover Mr Matheson from the water and did not broadcast a “mayday” call, leading to a 30-minute delay in paramedics attending.
The report said this “probably did not alter the tragic outcome of the accident”.
The MAIB’s findings also said the deckhand was under the influence of alcohol and this “almost certainly contributed to the accident”.
Alcohol consumption has been considered a contributing factor in 17 of 24 other fatal accidents between 1994 and 2016 involving fishermen boarding vessels.
The report said: “Duncan Matheson drowned because he was not wearing a life jacket when he entered the water from the tender and the skipper was unable to recover him on board. Mr Matheson’s BAC at the time of the post-mortem examination was 276 milligrams per 100 millilitres of blood, over five times the UK BAC limit for seafarers and commercial fishermen.
“The high BAC and presence of the hip flask strongly indicates that he had intended to consume alcohol during the working day.
“Given Mr Matheson’s known history of alcohol addiction, he might have appeared to be functioning normally before he boarded the tender.
“However, it is almost certain that his alcohol consumption was a significant factor in this accident.”