Modifications made to a trawler which sank with the loss of two lives reduced its stability, a report has found.
The Marine Accident Investigation Branch (MAIB) said the Nancy Glen capsized when a net became filled with mud as it tried to turn in Loch Fyne.
But changes to the vessel, including a new crane which was more than double the weight of the old one, meant it could not perform the manoeuvre.
Duncan MacDougall and Przemek Krawcyk died in the tragedy in January 2018.
The MAIB has called for the stability of small fishing vessels – under 15m – to be regularly assessed to prevent such incidents in the future.
The Crown Office has confirmed a Fatal Accident Inquiry will be held into the sinking but earlier this week it emerged a criminal investigation has been dropped.
A third crew member survived but the bodies of the skipper Mr MacDougall, 46, and Mr Krawcyk, 38, were not recovered until April last year.
The report concluded: “The MAIB’s investigation established that through life modifications to Nancy Glen, culminating in the replacement of the crane with a heavier model, had reduced the vessel’s stability, significantly increasing its vulnerability to capsize.”
Andrew Moll, the MAIB’s chief inspector of marine accidents, called for lessons to be learned from the case.
He said: “The capsize and sinking of Nancy Glen, which resulted in the tragic loss of two respected Tarbert fishermen, has again demonstrated the consequences of not knowing how stable a boat is.
“Too many of the UK’s small fishing vessels have no baseline measure of their stability, so their operators cannot assess the effect of material modifications or changes to fishing methods.
“The MAIB has recommended that the Maritime and Coastguard Agency implements changes to legislation to require both new and existing small fishing vessels to assess their current stability and to continue to monitor this throughout the life of the vessel.”
The Nancy Glen was built in 1991 and operated from its home port of Tarbert, Argyll and Bute.
The report said the twin rig prawn trawler set sail at about 22:30 on 17 January last year and worked through the night.
At about 17:50 the following day, almost 90 minutes after sunset, the vessel was part way through the last trawl of the day when it began to list to starboard.
The report found its starboard net became “fouled” with mud and debris.
The skipper, Mr MacDougall, tried to bring it under control but was unable to do so.
A 34-year-old crewman, who has not been named, shouted to his colleagues to get out before he plunged into the water.
But as the boat capsized in the darkness Mr MacDougall and Mr Krawcyk, who both lived in Tarbert, were trapped.
The alarm was raised by the third fisherman who was pulled from the water by the crew of a passing boat.
A specialist lifting barge was used to bring the wreck to the surface last April and the bodies of Mr MacDougall and Mr Krawczyk were recovered.
The MAIB had previously conducted a seabed survey of the ship, which had been lying at a depth of 143m (469ft).
At the time it had no plans to raise the boat but the the Clyde Fishermen’s Association raised nearly £300,000 through crowdfunding to finance a salvage operation to retrieve the bodies.
The Scottish government then stepped in to fund the operation to retrieve the boat, and the money previously raised was used to support the families of the men who died.
The MAIB report said the vessel’s reduced stability could be “directly attributed” to a series of modifications made since 2002.
But the most significant occurred in the weeks before the sinking when the trawler’s 700kg crane was replaced on the shelter deck with a 1500kg model.
To compensate, a steel lifting post was changed for an aluminium one.
But the report said: “Although the weight difference was considered, no empirical assessment regarding the effect on the vessel’s stability was carried out prior to completing these modifications.”
It later added: “The cumulative effect of those modifications, culminating in the replacement of the crane during the 2017/18 Christmas layover, was to reduce the vessel’s stability, significantly increasing its vulnerability to capsize.”
The report also said the Nancy Glen’s registered length was 11.98m – a metre shorter than its actual length – which meant that stability criteria for fishing vessels longer than 12m did not apply.
‘Exposed to risk’
The MAIB said of the 5,603 UK fishing vessels registered by the end of last year, 4,872 (87%) were less than 12m and therefore subject to less stringent stability checks.
The report said: “None of these have ever been subject to any stability criteria relating either to their original build condition or following through life modifications.
“Unless stability standards are introduced and retrospectively applied, these vessels will remain exposed to unassessed risk until they are retired from service.
“Vessels engaged in trawling and other forms of bulk fishing are particularly at risk.”
Meanwhile, the MAIB found there was insufficient evidence that fatigue contributed to the accident.
But it noted: “The cumulative effect of long working days (routinely 20 hours from port departure to arrival for 5 days each week) could have impacted on the crew’s ability to react to an emergency.
“Long hours with limited breaks remain a common feature of commercial fishing.”
The Clyde Fishermen’s Association said: “We will forever regret the tragic incident of the Nancy Glen’s loss which occurred on the 18th of January 2018. We will also always pay respect to the men lost and their families, friends and communities impacted.
“Neither will we forget the support of local, national and global communities.”
The association thanked the MAIB, Police Scotland and the Scottish government as well as “countless others” who helped in the wake of the tragedy.
It concluded: “The MAIB report has suggested a number of changes to under 15 metres fishing boats in moving forward which may help to improve safety.
“We will continue to be supportive of all efforts to improve the safety of all who go to sea.”