The government's plans for the Coast Guard's new fisheries and science vessels produced a ship some engineers considered so unstable it was unseaworthy and if sailed on the open ocean would capsize in heavy seas, CBC News has learned.

The issue was discovered in 2012 once the blueprints of the government-ordered design were sent to Vancouver Shipyards, where three of the ships are being built under the government's shipbuilding strategy.

Engineers there uncovered what they believed to be a fault, which led to a re-design of the vessel and the addition of 8.4 metres to the ship's 55-metre length.

The changes increased the displacement of the ship by 610 tonnes, or roughly 24 per cent. Government literature about the vessels also suggests the ships will now travel half a knot more slowly.

Officials at the Department of Fisheries and Oceans, which oversees the Canadian Coast Guard, had previously admitted to CBC News there were design changes, but played down their significance.

"Some early underlying assumptions and calculation of weights and centres of gravity required changes," Frank Stanek, manager of media relations for DFO, said in a statement in 2014.

"The issue was satisfactorily addressed by the shipyard engineering team in close consultation with the government."

But CBC News has learned the design problem was considered so severe by the shipbuilders it was thought it would be unsafe to build and sail the vessels.

'Puzzling, perplexing'

Jeffrey Smith, the former head of shipbuilding for B.C. Ferries, said such a serious flaw should have been caught early.

"It would appear that there was a design oversight, leading up to the point where the shipyard took over," he said in an interview. "It sounds avoidable. It's puzzling. It's perplexing."

Seaspan's Vancouver Shipyards is building three vessels, seen here in a rendering from the company's website, as part of Canada's non-combatant ships program. (Seaspan)

Smith is a former chief engineer in the navy and once chaired the Canadian Institute of Marine Engineering. He said stability is one of the fundamental considerations of ship design. Questions about weight, centres of gravity and the ability of a vessel to right itself in various environments are not minor and are never left to the final design stages.

"You really want to do these things... as early in the process as possible, given the consequences of delay and the uncertainties of shipyard costing."

Program hit by delays

These are not the first stormy seas the Offshore Fisheries and Science Vessel (OFSV) program has weathered.

The program has been beset by delays and spending increases. The original plans set the budget at $244 million for three hulls and established a final delivery date of 2014.

Last week, CBC News reported government ministers had been warned the program's costs have grown $687 million.

The fisheries science vessels have been through several planning iterations, with different designs along the way.

It's the government's plans from 2012, when the program was well underway, that the shipbuilder worried were unsafe.

It has been suggested if industry had been left to do the work on its own, there wouldn't have been trouble.

"In 2012, when the Coast Guard asked Seaspan to review its initial OFSV design, we identified a stability issue," Seaspan, which owns Vancouver Shipyards, said in a statement.

"We immediately set to work with our customer to correct the problem well ahead of the project's production design phase. The outcome proved the value of collaboration with the Coast Guard."

In a new statement Friday, the Department of Fisheries and Oceans said it believed the vessel was never in danger of capsizing.

"Weight and stability are checked at every stage of the process. The design was stable and met the requirements set forth under shipbuilding regulations from Lloyds, our third-party regulator," the department said. "The design was adjusted as engineering proceeded from the basic full design to a blueprint for a fully equipped ship."

Ocean always a 'risky environment'

The first of the three ships is to be delivered in spring 2017 and will be named CCGS Sir John Franklin.

The ships are equipped with low aft decks and trawling gear to allow the Coast Guard to harvest the oceans and assess fish stocks as part of ecosystem assessments.

The work is performed on the open ocean wherever fishing is done, including in the sometimes dangerous waters of the North Atlantic and the North Pacific. The ships would also be used to assess stocks in Arctic waters.

"Operating a science platform with an afterdeck of a ship that's low to the water, doing things in very different environments — net trawls for fisheries, stopping and starting in heavy weather conditions — demands a high degree of safety, a high degree of regard for the stability of a ship," Smith said.

On Thursday, CBC News revealed the new Liberal government has moved to reform Canada's costly shipbuilding program, promising a new system to evaluate costs, launch quarterly public updates and provide annual reports to Parliament.

Public Services Minister Judy Foote is also hiring a shipbuilding expert to advise the government. Interviews for that job were scheduled to begin Friday.