A toilet overflow caused the Steamship Authority ferry Nantucket to miss its first round-trip between Vineyard Haven and Woods Hole Thursday morning, and tidal conditions in Woods Hole delayed the unloading of a later trip by about 10 minutes, boat line spokesman Sean Driscoll said.

The sewage overflow took place in the crew quarters Wednesday night, requiring crew members to put in extra hours fixing the problem, Mr. Driscoll said.

That time cut into the rest period that is required before crews go back to work, leading to the cancellation of the 5:30 a.m. trip to Woods Hole and 6:30 a.m. return.

“They didn’t have enough rest on the books to sail the boat,” said Mr. Driscoll, adding that the Nantucket’s 7:30 departure was slightly delayed.

“That’s all from an overflowed toilet,” Mr. Driscoll said. The cancellations are listed as for mechanical reasons, he added, because there is no more specific category.

The arrival of the 7:30 trip in Woods Hole was also delayed for about 10 minutes when a truck was unable to clear the exit from the freight deck.

“In certain tidal conditions . . . the angle of the ramp can hang up certain trucks, especially long trucks,” Mr. Driscoll said.

“That’s an issue we’re correcting by installing the new transfer bridges as part of the Woods Hole [terminal reconstruction] project,” he added.