PORT TOWNSEND — Those wondering why Washington State Ferries has passed over four boats offered for sale by BC Ferries at a time when Port Townsend needs a bigger ferry can forget about it.

The problem is two-fold, a state ferries spokeswoman said: an unsafe design for the Port Townsend-Keystone route and the Jones Act.

BC Ferries earlier this year announced it was seeking buyers for the retired Queen of Tsawwassen, Queen of Esquimalt, Queen of Saanich, and Queen of Vancouver, each of which is approaching 50 years old.

“The Queen of Tsawwassen is the one we’ve looked at the most,” said Hadley Greene, state ferries system spokeswoman.

“They’re double-ended ferries. But they have one navigational bridge, so that means the captain would have to back the vessel out,” she said.

“The bridge faces one direction, and we really need a double-ended ferry to work for Keystone.”

The Queen of Tsawwassen holds 138 cars and 989 passengers.

The necessity of backing the ferry out of the harbor, and its size, is an unsafe proposition at Keystone Harbor, which often strikes fear in ferry captains for its dangerous currents and its narrowness, she said.

Then there’s the Jones Act, which states that no foreign vessels shall transport passengers between ports or places in the U.S., either directly or by way of a foreign port.

It would take an act of Congress to change the law, state ferries officials have said.

Greene said there are no other state ferries that are small enough to safely operated in Keystone Harbor.

That is why the 50-car Steilacoom II is the only temporary replacement vessel the state could lease from Pierce County for the Port Townsend-Keystone route this summer.

The route has been without its two 81-year-old Steel Electric ferries since Nov. 20, when state Transportation Secretary Paula Hammond declared them unsafe.

Ferries based on the 64-car Island Home used in New England are planned for the route, but the first boat is not expected to be completed until 2010.