FERRIES: Bar below boat may help quell fast ferry wake

Sun | Local

* The interceptor helps lift the stern and point the bow slightly downward.

A simple, inexpensive device has reduced the passenger ferry Chinook's wake since it last sped through Rich Passage, state ferry officials say.

Last month, a 1-inch aluminum bar was bolted across the stern bottoms of the Chinook and its sister ship, Snohomish.

Water smacks against the bar, creating upward pressure that lifts the stern and points the bow slightly downward. That's the boats' optimum trim angle, the position that creates the least wake.

The boats' designer, Advanced Multihull Designs of Sidney, Australia, recommended the change after making it on another of its vessels.

"They contacted us and said this might help," said Stan Stumbo, Washington State Ferries' hull section supervisor. "We went out and tried it, and it did very, very well. It's dirt cheap and simple as a box of rocks."

The bars, called interceptors, were tested in shallow water near Keyport that's similar to Rich Passage but farther from shore.

The Chinook sometimes didn't meet the ferry system's wake wash standards when its trim tabs weren't used, Stumbo said, and the trim tabs caused steering problems. The interceptors serve the same purpose without causing steering problems or generating their own wake wash.

"What it does is make it so the Chinook and Snohomish meet our acceptability criteria all the way through Rich Passage," Stumbo said.

"It wasn't a magic wand, but it was a simple thing we could use to tweak the boat to its best performance."
