A fisherman died after falling overboard from a boat found to have deck walls lower than the minimum statutory height, an official report said on Wednesday.
The condition and standard of housekeeping on board at the time were "poor", the report said.
Deckhand Steven Robertson, 25, was lost overboard from the scallop dredger St Amant between around 12.45am and 01.45am on January 13 last year with no other crew members witnessing him fall into the Irish Sea.
The boat's owner, skipper and crewmen had an "extremely poor attitude to establishing and maintaining a safe working environment on board the vessel", the Marine Accident Investigation Branch (MAIB) report said, while precautions which might have prevented the accident were not put into practice.
Mr Robertson, from Dalbeattie, Dumfries and Galloway, was last seen on board the boat around 1.2 miles west of the Isle of Anglesey's South Stack at 12.45am but was not discovered missing until around 2am.
Because of a lack of witnesses, it was considered most likely that he fell over the vessel's aft bulwarks, probably while in the process of relieving himself overboard.
It was also possible that he tripped or slipped on part of the fishing gear or equipment that was stowed on the deck. He was not wearing a life jacket or beacon when he fell.
The investigation established that the 58ft dredger had been given an exemption from complying with the minimum bulwark height requirements contained in the Fishing Vessel (Safety Provisions) Rules 1975.
The arrangement of St Amant that led to the initial decision to grant the exemption had not been reviewed in accordance with the Maritime and Coastguard Agency's (MCA) procedures, meaning that parts of the vessel's bulwarks were less than the minimum statutory height.
The investigation also found that a large proportion of the deficiencies which had been identified during previous surveys and inspections of St Amant had never been confirmed as rectified.
The condition and the standard of housekeeping on board St Amant at the time of the accident were found to be poor while the written risk assessments for the operation of the vessel were inadequate.
The dredger was proceeding from Holyhead towards its intended fishing grounds in Cardigan Bay at the time of the accident.
Despite an extensive air and sea search, involving a Royal Air Force rescue helicopter, five RNLI lifeboats, other vessels and a police helicopter, Mr Robertson could not be found.
The owner of St Amant has been recommended to take action to improve both the safety of the working practices on board and the hazard awareness of the vessel's crew.
Recommendations have also been made to the MCA to review and clarify aspects of its survey and inspection policy for fishing vessels.
The report said the MCA has since written to the owner of St Amant requiring the height of the vessel's bulwarks to be increased.
And it said the boat's owner, Nightvalley Limited, has stopped working with the skipper of the vessel at the time of the accident.
A rail has also been installed above the existing solid bulwark along with a chemical toilet for use on the vessel.