Two Steamship Authority ferries, M/V Gay Head and M/V Nantucket, are out of service for the weekend, although the Nantucket is expected to be back in action Sunday night.

Both ferries had mechanical issues this week, breaking down Thursday. 

“The Nantucket had a bad shaft seal which needs to be replaced,” boat line spokesman Geoff Spillane told the Gazette.

The 49-year-old ferry, which can carry up to 50 cars and more than 700 passengers, was on its way Friday to Thames Shipyard in New London, Conn., where it is scheduled for the repair in dry dock Saturday.

“The plan is to have it refloated Sunday and back [in service] Sunday night,” Mr. Spillane said.

The M/V Sankaty, a freight boat that can carry 39 vehicles and 300 passengers, was deployed to cover the Nantucket’s trips, with the Gay Head — which can also carry 39 vehicles, but fewer than 150 passengers — taking the Sankaty’s schedule.

Then the Gay Head went out of service as well when its main engine turbocharger failed Thursday. The ferry now is at the authority’s repair facility in Fairhaven awaiting parts, Mr. Spillane said.

While there’s no timetable for the Gay Head’s repair, he said, the Nantucket’s return on Sunday will restore the normal ferry schedule.

In the mean time, according to an announcement on the Steamship Authority website, the boat line has added extra trips and is using the lift decks on the M/V Island Home in order to carry vehicles that had reservations on the out-of-service vessels.