The Western Tugger was towing a barge called the Arctic Lift on May 10, 2013, when a tow line snapped and struck a crew member.
The Transportation Safety Board released a report Tuesday identifying inclement weather and overloading as causes behind the accident, which happened about 60 kilometres southwest of Burgeo.
The report says while it was being towed the barge listed, which may have been the result of several factors including flooding through hatches that weren't properly sealed or unsecured cargo that shifted while en route.
Investigators say the tugboat's captain wanted to release the barge as a precaution in case it sank and directed a deckhand to the winch room to loosen a secondary brake that had been added to the winch to assist the main brake.
Moments later, the forward end of the barge rose out of the water and it capsized, the report says.
The safety board says the resulting strain on the secondary brake drum caused it to shatter and parts of it hit the deckhand, killing him.
A number of safety issues were flagged by the safety board including unsecured cargo, hatches that weren't watertight and an emergency tow release that could not be operated immediately.