The ferry Walla Walla, which had been sailing between Seattle and Bremerton, will be out of service for at least four weeks as crews repair a propeller that broke near Rich Passage last week.

Losing the 188-car Jumbo class boat for a month forces Washington State Ferries to shuffle its fleet yet again, likely meaning more backups on the already thin ferry system.

The state ferry system has recently resembled a game of Tetris. The Walla Walla was pulled from service Friday when the ship started to vibrate. It was replaced by the 144-car Chimacum, which itself had just replaced the 202-car Wenatchee on the Seattle-Bainbridge route, which is out for a year as it’s converted to hybrid-electric. Now, the 64-car Salish will remain on the Bainbridge crossing while the Chimacum stays on Bremerton.

The result of the puzzle is that both the Bremerton and Bainbridge routes have lost capacity. Bainbridge will carry 138 fewer cars between its two boats while Bremerton will carry 44 fewer. Bainbridge is the state’s busiest route, carrying 4.5 million rides in 2022 and more than 8 million before the pandemic.

The Salish was previously tied up near Port Townsend and not in use. If it turns out the ferry needs longer than a month, WSF may reshuffle its boats again, said WSF spokesperson Brian Vail.

The Walla Walla was tied up after crews noticed intense vibrations as they pulled into Bremerton and suspected propellor damage. Divers found that a blade on one of the propellors had been shorn off. The cause has not been found, but it’s not uncommon for a ferry to hit a log or some other object.

Initially, WSF hoped divers could fix the issue underwater, but it later determined the boat needed to be drydocked — lifted from the water — to make the repairs. The company Vigor, which has a shipyard on Harbor Island, is likely doing the work, Vail said.

This is the second time this year the Walla Walla has been pulled from service for emergency repairs. Earlier this year, fuel contamination caused cascading failures on the boat’s generators, killing power to the steering and causing the ferry to beach onto Bainbridge Island.

Built in 1972, the Walla Walla has come to symbolize the state’s aging and tired fleet of boats. Just nine of the 21 are considered in good shape and three are already or nearly due for retirement. State lawmakers budgeted $1.3 billion in 2022 to build five new hybrid-electric boats, but negotiations with Vigor to do so fell apart and the state has not yet found a replacement shipbuilder. The earliest a new boat could arrive is 2027.

Meantime, the state has begun converting its largest Jumbo Mark II boats to hybrid-electric. When the Wenatchee returns in fall of 2024, the Tacoma will be pulled from service followed by the Puyallup in 2025.