The Steamship Authority has ordered a replacement for one of the main generators on the ferry Island Home following a string of malfunctions which have disrupted service.

The ferry missed eight trips in December alone, according to the boat line. Through the month of November, 13 of its 3,146 scheduled trips had been cancelled — nine due to breakdowns and four due to bad weather.

By way of comparison, the ferry Martha’s Vineyard missed eight of her scheduled 3,718 trips during the same period. And the boat which the Island Home replaced, the venerable Islander, missed only three of 3,908 journeys in 2006 for mechanical reasons and 16 due to bad weather.

Carl R. Walker, director of maintenance and engineering, said the faulty number two generator on the Island Home would be replaced later this month. Electrical faults, particularly associated with the generator, had been responsible for most of the new boat’s problems.

The various mechanical issues with the Island Home have earned it the unfortunate nickname Broken Home in some quarters, but Mr. Walker said the boat had actually worked fairly well in the nine months since it entered service.

“There are always some bugs with a new vessel,” he said. “There is also a certain amount of familiarization to do, just knowing how to troubleshoot things.”

He cited the example of one problem which caused a service disruption in May, when the bow doors would not open. It was relatively easy to open the doors manually, he said, but the crew had not known how. “But they do now, so that shouldn’t be a problem again,” he said.

“Any service disruption is unacceptable, but the fact is over the year the boat made something like 99.8 per cent of its trips without problem.”

The SSA’s service problems with the new boat have been compounded by the fact that one of its three slips at Woods Hole is unavailable because it is being used as a substitute berth for the freight vessel Governor, which otherwise would be tied up at the Fairhaven maintenance facility, while work is done at Fairhaven.

Because the freight boat service also stops early during the off-season, only one slip is operative for the late runs.

In an open letter to the SSA board and management published in last week’s Gazette, Jeffrey Parker of Chilmark complained that he had been left stranded for the night in Woods Hole after the Island Home broke down and could not make its 6:15 p.m. run on Dec. 18.

He accused the boat line of having failed to provide a substitute vessel to transport standby passengers.

But boat line senior managers subsequently explained a backup vessel had been supplied, although after some considerable delay caused in part by the slip congestion.

With the Island Home broken down, blocking one slip and the two freight boats blocking the other two, it was necessary to move the crew from the Island Home to the Katama and get it started up before any service could resume, managers explained.

“As soon as we realized we could not get the Island Home operating, we transferred the crew to the freight boat and they did make the trip in order to carry cars that had reservations on the Island Home. We ran an extra trip too on the Martha’s Vineyard that night,” said SSA general counsel Stephen Sayers, adding:

“But because the Island Home can carry so many cars and was fully booked, those that were on standby couldn’t get across.”