Steamship Authority engineers are working to iron out some unexpected wrinkles in the performance of the new freight ferry, M/V Barnstable.

The former offshore service vessel was poised to begin service on the Nantucket route in late January when a thermostat malfunction damaged an engine cooler seal, general manager Robert Davis told the Steamship Authority port council Tuesday.

Engineers made another discovery while repairing the cooler, which director of engineering and maintenance Mark Amundsen compared to a vehicle radiator.

“We needed to add a block heater to keep the viscosity of the lubricant going,” Mr. Amundsen said. “These vessels previously operated down in the Gulf and weren’t used to having these cold temperatures.”

The Barnstable had more surprises in store after the repairs, when it began the 30 mile cruise to Nantucket.

Crews at first struggled to load trucks aboard the new freighter, Mr. Davis said. 

“It’s a learning curve for our crews and our terminal personnel,” he said. “Initially, it was taking upwards of 40 minutes to load the vessel.”

On a positive note, Mr. Davis said, the single-ended ferry is wide enough that tractor-trailer drivers can turn their rigs around on deck, easing the loading and unloading processes.

The freight itself has posed another challenge: Once the Barnstable is loaded to about three-quarters its capacity, the vessel’s draft — depth of hull below the water line — increases significantly, requiring a new letter from the Coast Guard allowing the ferry to take its full payload of nearly 1 million pounds.

“It puts it into a different operating parameters,” Mr. Davis said. The Coast Guard letter was expected Wednesday, Mr. Amundsen said.

The Barnstable also has been slower than expected, even with lighter loads.

Intended to cruise at an average 12.5 to 13.5 knots —roughly 14.4 to 15.5 miles per hour — the new ferry posted markedly lower speeds in its initial runs.

“We were looking at closer to 10 and a half to 11 and a half knots for a while there,” Mr. Davis said.

Those speeds have since improved to 11.2 to 12.2 knots, allowing the Barnstable to stay on schedule, he said.

Mr. Amundsen told the port council that engine programming should solve the speed and stability issues.

“We’re having Brunvoll, the maker, adjust the engine horsepower and speed in relation to the pitch,” he said.

The Barnstable — like its two sister ships, M/V Aquinnah and M/V Monomoy, which are still at Alabama Shipyard in Mobile, Ala. — was shortened by 24 feet in the midsection as part of its conversion from an oil and gas service vessel to a Steamship Authority ferry.

The midbody work was needed in order to install water-tight bulkhead compartments, which provide structural stability and are required safety measures aboard a passenger ferry.

The Aquinnah, which will serve the Vineyard, is expected to be ready for sea trials by the end of February and the Monomoy is scheduled for completion in June, Mr. Amundsen said.

Among other business Tuesday, director of shoreside operations Alison Fletcher gave the port council an update on the Blue Line standby program for Island motorists, which began a 90-day pilot Jan. 4. All other standby travel has been suspended.

Through Feb. 4, Ms. Fletcher said, 227 vehicles used the Blue Line to leave the Vineyard without a reservation.

In Woods Hole, where the same-day service was first used on Jan. 10, 125 Island vehicles had taken advantage of it by Feb. 3, Ms. Fletcher said.

“Generally speaking, it has been well received, and customers have been happy as far as I’ve been aware,” she said.

The Steamship Authority port council is an advisory group for the boat line board of governors, which holds its next meeting Feb. 18.