A city-sponsored commuter ferry that was out of service for more than two weeks in November has broken down again.

The Rachel Marie, one of two 72-foot catamarans that sail between Kalaeloa and Aloha Tower, has been docked all week after experiencing engine problems, and is expected to remain idle until at least Monday.

A rebuilt engine that was installed in the vessel's port hull after the earlier breakdown is now having trouble, officials said.

The 6 a.m. sailing from Kalaeloa, and 5:20 p.m. sailing from Aloha Tower, have been cancelled until repairs are made. Shuttle buses are available as temporary replacements.

The Rachel Marie has had difficulties since the ferry program, dubbed TheBoat, was launched less than four months ago.

The boat's maiden voyage in Hawaiian waters was delayed for several days in September after the port engine began sputtering. A faulty master control unit was replaced.

Mayor Mufi Hannemann said he hopes the vessel will prove more reliable in the future.

"It's an old boat, and we knew that going in," he said. "We'll keep working on it, and we'll keep praying."

The mayor stressed that the remaining ferry is making two out of three of the scheduled trips each morning and afternoon.

"I'd feel real bad if both of them were broken down," he said.

The city has considered replacing the Rachel Marie, but no comparable vessels are immediately available, and a new one would be too expensive, Hannemann said.

"We don't want to put an unreliable boat out there," he said. "We're trying to be as quick as we can, but at the same time proceed prudently and cautiously."

The Rachel Marie and its sister, the Melissa Ann, were shipped here on a barge after years of service in waters off Alaska and Washington state.

The ferry service and five linked bus routes are expected to cost $6 million for a year. Federal grants are providing $5 million.

Hannemann has characterized the ferries as an important alternative to driving on the island's crowded roads and freeways. But some City Council members and others have questioned whether the program is a boondoggle that will end when the grants are exhausted.

TheBoat has a core of loyal riders, but the 149-seat ferries are often less than half-full. Ridership dropped sharply over the past month because of poor weather, the holiday season, and the engine trouble, officials said.

Fewer than 2,000 passengers rode TheBoat in December, compared to 14,000 in the previous 2 1/2 months.

The city's ferry contractor, Hornblower Marine Services, is paying for the Rachel Marie's repairs, and will credit the city for the lost service, officials said.

Reach Johnny Brannon at jbrannon@honoluluadvertiser.com.

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