The TSB released its report Tuesday on the Oct. 25, 2012 incident involving the MV Nanny.
The MV Nanny was leaving Baker Lake and carrying oil products when it spent two days grounded in Chesterfield Narrows. The area is marked by unlit beacons and allows for little margin of error.
The TSB found that the ship ran aground because it had deviated from its charted route.
The ship had to steer off-course to pass another tanker, but then was never returned to its proper path. It instead proceeded on a parallel route, about a nautical mile off-course.
"The vessel was steered a bit too much to the east and to the north and eventually it was grounded," said Pierre Murray with the TSB's Atlantic bureau.
The TSB says a lack of communication between the bridge officers was a factor in the grounding.
No injuries or pollution were reported. The double-hulled ship was badly damaged on its hull and rudder but not the tanks.
It was the second time the Nanny had run aground in Nunavut waters. In September 2010 the Nanny was lodged in Simpson Strait near Gjoa Haven while carrying more than 9 million litres of diesel.
The TSB says Coastal Shipping Limited, the MV Nanny's owner, has since created a "confined waters policy," a checklist of procedures to follow when entering narrow waterways. The board also says lighted beacons in Chesterfield Narrows would help ships travel safely through at night.