Passengers who rely on Coupeville-to-Port Townsend ferry service breathed a sigh of relief Thursday when a relief boat in South Puget Sound passed inspection, clearing the way for the resumption of two-boat service Sunday.

The Chetzemoka, which ordinarily travels the route from Point Defiance in Tacoma to Vashon Island, is returning to service in Admiralty Inlet Sunday morning for the first time since 2011.

The Coupeville-Port Townsend route was reduced to one boat since Wednesday after the Kennewick was shut down following an inspection that revealed significant signs of wear to the vessel’s rudder components.

It is the same issue that temporarily knocked the Salish out of service in early May.

“The fix quite honestly is a matter of days,” said Ian Sterling, a spokesperson with Washington State Ferries, comparing it to replacing worn-out brake pads in cars.

“Dry dock availability is the problem.

“We are not able to get it to a dry dock for a while. The quickest we could get it into service is the middle of July.”

Out of precaution, divers examined the Chetzemoka’s rudder Thursday morning and the boat passed inspection, avoiding a potential headache for ferry riders between Coupeville and Port Townsend over the next month.

The Chetzemoka, Salish and Kennewick all belong to the Kwa-di Tabil class of ferries that carry 64 vehicles and are the only ones in the fleet capable of navigating the difficult passage into Keystone Harbor. They were commissioned to replace the 80-year-old Steel Electrics that were retired in 2007.

If the Chetzemoka hadn’t checked out OK, the Coupeville-to-Port Townend route would have been forced to continue to operate with one vessel until the Kennewick returned in mid July.

The rudder components at issue with the Kennewick are hinge bushings and pins that are worn beyond their allowable limits, Sterling said.

“The parts are designed to wear out,” Sterling said. “We just didn’t expect them to wear out this quickly.”

The Chetzemoka started service in November 2010, followed by the Salish in 2011 and Kennewick in 2012.

Seattle’s Vigor Industrial, formerly Todd Pacific Shipyards, constructed all three ferries.

Freeland-based Nichols Brothers Boat Builders built the superstructures for all three vessels.

The Kennewick and Salish have offered seasonal two-boat service in Admiralty Inlet since 2012.

“These aren’t old vessels,” Sterling said. “We’re working with the rudder manufacturer to figure out why this is happening.”