Delaying efforts to replace Canada's 40-year-old navy supply ships will damage the service's frigate, according to documents obtained by CBC News.

Extending the wait for new ships will create a problem called "rust-out," said navy Commodore Kelly Williams in a 2009-2010 Maritime Staff Capability Plan, copies of which were obtained by CBC News.

A $2.9-billion program to replace the two supply ships was put on hold in August, because bids came in over budget.

The navy decided to refit the two ships for the time being. But that is an expensive alternative, according to Williams, who prepared the report when he was assistant chief of Maritime staff.

"Maintaining the obsolescent tankers is costly and will put further pressure on the already constrained [repair budget] and further delays in the mid-life refit for Halifax class [frigates] which will lead to rust-out," he wrote in the 2009-2010 report.

"Rust-out" is caused by repeatedly sanding warships, which leads to hulls becoming "progressively thinner and more fragile," said Eric Lerhe, a retired commodore living in Dartmouth.

Lerhe likens it to patching up an aging car.

"How many times can you take a car to the autobody shop and smack on the Bondo?"

In the capability plan, Williams said efforts to preserve the two supply ships will put more pressure on the navy's repair budget, which will cause further delays in upgrading the Halifax-class frigates.

'Only enough money for 2' ships

A spokesman for Defence Minister Peter MacKay said the federal government still wants to buy new ships, through a project known as joint support ship, or JSS.

The program is a disaster, according to Liberal Senator Colin Kenny, who chairs the Senate's standing defence committee.

"The navy only asked for three [ships] when it knew it needed four," he told CBC News. "But the costs have come in that there's only enough money for two. And if Mr. MacKay thinks things are on track, he really doesn't know what's happening."

Navy officials were not available for comment.