The Steilacoom II, the only vessel ferry officials has to serve the Keystone to Port Townsend ferry route, will be out of service for a weekend in January.

The route will be closed Saturday and Sunday, Jan. 9 and 10, so the 50-car ferry can undergo its annual inspection.

Ferry officials are announcing the closure well in advance so riders can plan ahead, according to a news release from Washington State Ferries.

Riders are advised to used the Mukileo/Clinton and the Edmonds/Kingston run as an alternative to travel to and from the Olympic Peninsula.

Like all ferries, the Steilacoom II is required by federal law to undergo a U.S. Coast Guard inspection every year. This inspection includes items such as inspecting the condition of lifesaving equipment, verifying proper operation of navigation equipment and fire suppression systems and observing crew performance during emergency drills, according to the news release.

In planning the timing of the inspection, officials talked with folks from Port Townsend and Coupeville. Weighing the anticipated ridership, the expense of chartering passenger-only service and installing temporary passenger loading and unloading facilities, and the short duration of the inspection period, it was decided to close the route for one weekend.

Typically, Washington State Ferries performs annual inspections over a two-week period at its Eagle Harbor Maintenance Facility on Bainbridge Island. However, because the ferry system doesn’t have any other vessels capable of operating out of Keystone Harbor, crews will perform the inspection over a two-day period in Port Townsend, according to the news release.

Work continues to build a ferry that will permanently serve the route. Seattle-based Todd Pacific Shipyards, with help from Nichols Brothers in Freeland, is halfway through an 18-month construction for the 64-car Chetzemoka, which is scheduled to start serving the route in the late summer 2010.