The Steamship Authority freight ferry M/V Gay Head was taken out of service this week after a four-inch crack was discovered above the waterline in the vessel’s aft (rear) hull, according to an announcement from the boat line late Friday afternoon.

The Gay Head was at the SSA’s maintenance facility in Fairhaven on Friday and would sail Monday to New London, Conn., for repair in dry dock at Thames Shipyard, according to the announcement.

In its place, the announcement continues, M/V Sankaty will ply the Nantucket route over the weekend and the Martha’s Vineyard route next week, steaming straight from Nantucket to Woods Hole on Sunday night instead of to Hyannis.

Monday’s 11:30 a.m. freight round trip from Woods Hole, with 12:45 p.m. return from Vineyard Haven, is canceled.

The Sankaty instead will load, in Woods Hole, traffic scheduled for the Gay Head’s regular 10:45 a.m. Hyannis departure. The Nantucket-bound freight trip will depart at 11:15 a.m. from Woods Hole, according to the SSA announcement.

“The Reservation Office will contact those customers scheduled on the 10:45 a.m. trip, which is scheduled as a hazardous materials trip, and tell them to report to Woods Hole,” the announcement continued.

“The M/V Sankaty will then run one round-trip between Nantucket and Hyannis, then the scheduled 6:45 p.m. departure from Nantucket to Hyannis will instead depart Nantucket at 8 p.m. and return to Woods Hole.”

This Sankaty schedule will remain in effect until at least Wednesday, August 3, the announcement continued, with decisions on future service to come once boat line officials find out how long the Gay Head will need to be in Connecticut for repairs.