The Transportation Safety Board has found that the capsizing and sinking of a tugboat near the Champlain Bridge construction site last year was due to an insufficient assessment of safety risks and a lack of documented operating procedures.

The Ocean Uannaq sank on April 1, 2016, about 300 metres from a large platform east of the existing Champlain Bridge which had been set up for workers to use as a base of operations.

The company responsible for the construction, Signature on the St. Lawrence Group, said at the time that workers were carrying out marine excavation work when one of the three tugboats capsized and sank to the bottom of the river.

The two workers on board were able to jump to safety on a neighbouring boat before the Ocean Uannaq filled with water.

Situation unfolded rapidly

In its report, the TSB said the capsizing of the Ocean Uannaq occurred quickly, beginning around 4:30 p.m.

As part of the excavation work, the Ocean Uannaq and a second tugboat were working alongside the Ocean Catatug 1, which was attached to the barge.

T​he report found the master of the Ocean Catatug 1 was new to the job and also "made a series of decisions" that contributed to moving the barge — including raising the upstream spuds, which are structures used for mooring, before the downstream spuds.

Boat capsize Montreal Champlain Bridge

The Ocean Uannaq was pulled from the water in May 2016. (The Transportation Safety Board)

"When one of the downstream spuds jammed as it was being raised, the barge and attached tug pivoted with the strong current around the jammed spud," the report said.

Due to a combination of hydrodynamic forces and the tugboat making contact with the Ocean Catatug 1's port wire, the Ocean Uannaq was unable to "move away from the rapidly developing situation."

The boat sank to the river bottom later that evening, a few hours after the workers made it to safety.

There were no injuries and no pollution as a result, said the TSB.

The Ocean Uannaq was pulled from the riverbed on May 28.

Tugboat's radio beacon not registered 

In its findings, the TSB points to safety management and oversight — a widespread problem, it says.

In this case, it found that both the tugboat owner and operator had not assessed the risks associated with complex marine operations before the boat was out on the water.

The investigation also found that those on board "were left to make ad hoc decisions" since there was no operating guide in place.

New Champlain Bridge

The tugboats were being used for excavation work on the new Champlain Bridge. (CBC)

The TSB also found that there were a number of communication issues at the time the boat capsized.

The Canadian Coast Guard couldn't figure out which vessel was transmitting a distress signal because the radio beacon on the tugboat had not been registered.

The TSB also noted that communications for the tugboat and barge operations were carried out on four separate radio frequencies.

Measures taken since accident

The TSB also noted that Signature on the St. Lawrence Group has since taken action after holding its own internal investigation.

The company has hired an assistant marine superintendent to develop procedures and hold a safety workshop after the incident.

As a result of the boat's capsizing, the TSB noted that the company has now ensured that all marine operations are on the same radio frequency.