RICHMOND, B.C. - The Transportation Safety Board says modifications made to a commercial sports fishing vessel led to a fatal accident near Tofino, B.C.

The 10-metre-long catamaran left Tofino on April 30, 2017, at about 9:30 a.m. with one operator and four passengers for a day of fishing.

The safety board says that during the next few hours as it anchored at different fishing spots, the Catatonic was observed to take on water.

The board says the bilge pumps, navigation and communications equipment stopped working when the operator was unable to start the engines before the vessel tipped.

A search-and-rescue team recovered all five people from the water, but two passengers were pronounced dead in hospital.

The names of those who died have not been released, but the RCMP said last year that two Alberta men, who were 32 and 42, were killed in the accident.

The safety board says significant parts of the vessel had been modified, including changes to the original design that allowed two batteries to operate separately. That was modified so both batteries, acting as the vessel's only power source, charged and drained simultaneously.

The board says the operator used a personal cellphone to call for help. An accurate position could not be provided to rescuers, so it took about 90 minutes for a search-and-rescue team to spot the vessel.

“The length of time spent searching for the vessel and the fact that the Catatonic did not have a life-raft meant that the passengers and the operator were immersed in cold water for approximately one hour and 40 minutes before they were recovered,” the board's report says. “They were therefore subjected to cold water immersion and associated cold water shock.”

The report says the Catatonic carried flares that had expired and remained stowed on board when everyone went into the water.

“The investigation found that the Catatonic's stern sank primarily due to water ingress into the vessel's pontoons and stern buoyancy compartments,” the board said in a news release Tuesday.

“Modifications made to the vessel allowed the water shipped on deck to first enter the fish boxes and then drain into the pontoon bilges. Holes that had been made in the shipside and the bulkhead also allowed the water to enter the pontoons and into the stern buoyancy compartments and contributed to the stern's sinking.”