Details of the collision and subsequent line ruptures are contained in an investigation of HMCS Athabaskan's tow to Halifax after it underwent a $21.7 million refit in St. Catharines, Ont.
The series of incidents took place between Boxing Day and Dec. 30 of 2012 in the Gulf of St. Lawrence and off the coast of Cape Breton.
The May 2013 report, obtained under access-to-information law, says the punctures require 18 square metres of steel to be replaced. Another 711 square metres of the ship needs fresh hull coating because the broken lines rubbed against the vessel, while rails, stanchions and a smashed sonar operator compartment window also have to be replaced, the report says. The military says some of those repairs have been completed.
The navy declined to make someone available for an interview. But Defence Department spokeswoman Tina Crouse said in an email the repairs would cost approximately $2 million.
The report says the Defence Department was invoiced about $546,000 for a second tugboat company to complete the tow from Sydney, N.S., to Halifax, on top of the $707,000 the department has been billed for the initial leg of the journey.
Investigators say one of the two tugboats involved in the operation suddenly lost power in the Gulf of St. Lawrence between Sept-Iles, Que., and the Magdalen Islands on the morning of Dec. 26 when an air leak caused the clutch to disengage.
A diagram in the 41-page report shows HMCS Athabaskan continuing forward, striking the Ocean Delta tugboat. The tug then spins around, striking the navy ship along one side while its fenders "burst as a result of the force exerted on them during the collision," the report says.
The six punctures all occurred between three to four metres above the waterline, the investigation says.
The report says a second tugboat took control of the towing while repairs were carried out on the Ocean Delta, and HMCS Athabaskan was then towed to Sydney, N.S.
On Dec. 28, the tow to Halifax resumed. Then, over a course of hours, four lines snap while the ship is about 10 kilometres off the rocky coast of Scatarie Island. The report says winds did not exceed 45 kilometres per hour and waves were between one to two metres at the time.
The first tow line snapped at 10 p.m. A search and rescue helicopter was deployed by the Joint Rescue Co-ordination Centre to bring personnel onto the drifting ship to secure a new line, which was done early on the morning of Dec. 29.
That tow line snapped about five hours later, and then a mooring line was used to continue the tow. But that line also broke a few hours later, and another mooring line was attached.
On Dec. 30 at about 3:40 a.m., that line broke. A third mooring line was then attached to HMCS Athabaskan to return it to Sydney.
Investigators say in their report they couldn't determine why the tow lines broke. But they say the mooring lines weren't intended for towing and "failed as a result of being used outside of their intended purpose."
The report calls on the navy to follow standard towing arrangements for the Iroquois-class destroyer from now on.
It also recommends that in the future, the navy have a back-up towing line attached to the bow of a destroyer and then left to drift alongside with a buoy attached in order to make it easier for a second tugboat to assist, if necessary.
The report also says the navy should do a more thorough job during contract talks of checking on a contractor's safety record, experience with warships and emergency plans.
Crouse said the Defence Department is developing a new "statement of work" document for use in any future tow contracts that incorporates all of the report's recommendations.
Philippe Filion, a spokesman for Ocean Group, the parent company of a subsidiary that owns the tugboats involved in the HMCS Athabaskan tow, said the plans for the journey and the towing arrangement were provided to the navy and officers reviewed and approved them.
Filion said his company has a good record and had sufficient experience to carry out the tow.
"An incident like this due to a mechanical problem doesn't happen often, but it can happen," Filion said. "We have to learn from what happened, but it's not a problem of experience in this kind of operation."