The Alaska Marine Highway System is waiting for the prognosis after a full-body scan of the state ferry Matanuska, looking for rusted steel — the equivalent of a cancer scan of the 61-year-old ship.

The Matanuska has been out of service for 18 months after it went into the shop for its annual winter overhaul, only to find a lot more “wasted” (rusted) steel in its hull, decking and other areas of the ship than expected.

That prompted the scan, which has been completed. Marine architects are working up a cost estimate, said Craig Tornga, marine director at the ferry system. The estimate is expected later this month.

“Before you can make a decision, you need information,” he said, explaining that state officials will look at the cost of repairs, the remaining life of the ship, the needs of the fleet and a potential schedule for constructing a replacement vessel.

Adding all that up, management will decide whether to seek funding to put the Matanuska into drydock for extensive steel replacement or end its maritime service in Alaska.

The state does not have the funds to build a replacement vessel, which would take several years to design and construct.

With the Matanuska out of service, the ferry system has been running either the Columbia or the Kennicott to maintain once-a-week mainline service through Southeast.

The Matanuska is the oldest ship in the fleet by one year over the Tustumena, which serves Gulf of Alaska communities. The state has been designing a replacement for the Tustumena, but design work has been delayed multiple times and the shipbuilding has yet to go out for bid. The earliest a replacement for the Tustumena could be ready, state officials have said, would be 2027.

Print-outs from the scan of the Matanuska show a lot of red, Tornga said, explaining that areas where the steel has lost more than 25% of its thickness show up as red on the report.

Some of the worst areas include the car decks, bow-thruster tanks, the hull’s double bottom and internal voids between bulkheads and between floors and the bottom of the hull.

A contractors’ crew working at the Vigor shipyard in Ketchikan crawled through the voids with an ultrasonic scanner, measuring the thickness of the steel. “They have to physically crawl each tank,” Tornga said.

Any areas with more than a 25% thickness loss need to be replaced, according to U.S. Coast Guard rules.

Saltwater and salt spray take a toll on steel ships, he said. And while he has more than 30 years’ experience working in the maritime industry, “I’ve never operated 60-year-old vessels before.”

The Matanuska was constructed in 1963 at Puget Sound Bridge and Drydock in Seattle. The shipyard closed down in 1987.