The Port Townsend to Coupeville ferry route is back to one-boat service due to a mechanical problem on the Chetzemoka.

Engineers on the 64-car ferry discovered a small leak in the vessel’s keel cooler, which prompted officials to pull the Chetzemoka from service, according to an email from Marta Coursey, spokesperson for Washington State Ferries.

The problem was discovered before the vessel went into service early Tuesday morning. Coursey said that divers are assessing the leak to the cooler, which is located outside the Chetzemoka’s hull. They should know soon whether the Chetzemoka will have to be taken into drydock to make repairs.

The keel cooler circulates fresh water from the diesel engines through tubes that help  cool the Chetzeomka’s service generator. The vessel is currently moored on the Port Townsend side of Admiralty Inlet.

Ferry officials will submit a repair plan to the United States Coast Guard later today.

The breakdown of the Chetzemoka leaves only one vessel crossing Admiralty Inlet from Coupeville to Port Townsend. The ferry system’s newest vessel, the Salish, was operational in time for the busy Fourth of July weekend. It has been nearly four years since the route has enjoyed two boat service during the busy summer months.

Numerous scheduled sailings had to be canceled today. Canceled sailings include the 10:30 a.m., noon, 1:30 p.m., 3 p.m. and 4:30 p.m. from Port Townsend and the 11:15 a.m., 12:45 p.m., 2:15 p.m., 3:45 p.m. and the 5:15 p.m. sailings from Coupeville.

Coursey said she doesn’t know yet whether the repairs will effect Wednesday’s sailing schedule.

She said staff is calling riders who had reservations on the Chetzemoka and telling them they will be moved to the Salish.