Despite repair crews' best efforts, TheBoat's disabled sister ferry will not begin service from Kalaeloa Harbor to Aloha Tower this morning.

The problem that forced cancellation of yesterday's inaugural cruise of the second boat turned out to be a faulty master control unit in the port or left engine. A new part was ordered from North Carolina that may arrive today, city spokesman Bill Brennan said.

As for when the second ferry may begin operating, "It'll be day to day," Brennan said last night.

The 72-foot catamaran, the Rachel Marie, was supposed to have joined its sister ship, the Melissa Ann, yesterday morning in offering O'ahu commuters 55-minute ferry rides between Kalaeloa and Aloha Tower's Pier 9.

But the Rachel Marie developed a problem with its engine's master control unit just before entering service yesterday.

So about 35 passengers hoping to ride the vessel were offered rides into town aboard TheBus — or a wait for a trip aboard the Melissa Ann.

Eighteen passengers took an express bus from Kalaeloa to Aloha Tower instead of the ferry.

"Some of them decided they would wait an hour to take the next" ferry, Brennan said.

Mechanics for the engine maker, Pacific Detroit Diesel, were analyzing the Rachel Marie's damaged engine last night.

The $5 million pilot program for TheBoat began Sept. 17 and is scheduled to run for one year. The Melissa Ann has been carrying about one-third of its capacity of 149 passengers.

"We actually had a very good first week," Brennan said. "It's a little disappointing the Rachel Marie couldn't get under way as scheduled. We apologize for any inconvenience it may have caused those passengers who hoped to take the inaugural voyage into town."

The Rachel Marie's port and starboard engines "ran all weekend and did well," he said.

But just before its scheduled 6 a.m. departure yesterday, he said, "one engine was running well and one was kind of sputtering. To err on the side of caution, we said, 'Let's not make this run.' "

The Rachel Marie and Melissa Ann were built in Freeland, Wash., in 1988 and were last home-ported in Seattle. They are registered out of Alaska, according to Coast Guard spokesman Lt. John Titchen.

The Rachel Marie passed a Coast Guard inspection on Wednesday and was cleared to operate Friday, Titchen said.

During last week's inspection, TheBoat officials told Coast Guard inspectors they plan to replace or rebuild the Rachel Marie's engines within six months, Titchen said.

But there was nothing in the inspection that indicated any problem that would keep it from sailing yesterday, he said.

TheBoat officials contacted the Coast Guard yesterday to report that an engine electronic control module had failed — although they were not required to report the problem, according to Titchen.

"They detected the situation before the passengers embarked," Titchen said. "They did the right thing and let us know. These things happen. Things break down."

Last week's inspection involved looking at the engines, exhaust and other systems.

The crew of the Rachel Marie also held emergency drills.

"Everything operated fine," Titchen said. "They did quite well with their drills. The crew was very professional, very capable."

Last week, the City Council approved a plan to encourage ferry ridership this week by temporarily suspending the normal $2 fares to ride TheBoat and connect to TheBus.

Reach Dan Nakaso at dnakaso@honoluluadvertiser.com.