Guemes Ferry: Z-Drive in Cross Current
The Guemes Island ferry run is only one kilometer from dock to dock, but its challenges are significant say the operators. The channel between Anacortes Washington and little Guemes Island in Puget Sound has tidal flows up to four knots. Winds can blow from either end of the short channel. When these blow against the flow of the tidal current they can create short sharp six-foot seas coming broadside on the 124x24-foot ferry with its 20 to 22-car capacity.
Capt. Monty Hughes has extensive experience on a variety of vessel types and currently also captains a twin screw whale watch boat. But he finds that wind and tide can create particular challenges to operating the little ferry on this route.
Highly respected Seattle naval architect the late Philip F. Spalding, who understood the challenges of the strong tides and narrow channels common to Pacific Northwest waters, designed the ferry. Wisely he specified a pair of z-drives located one on each end of the ferry and on opposing sides. This gave the ferry, built by Gladding and Hearn, excellent maneuverability including the ability to counter the cross currents while crossing the channel.
The Guemes was built by Galdding and Hearn in 1978. The ferry made the trip through the Panama and up the west coast under her own power, which was originally a pair of two-stroke 12V-71 diesels. In 1990 these were changed out for 12V-92 engines rated at 529 hp each. At the same time the original drives were traded for a pair of Ulsteins. This past October the ferry was taken out of service for a major refit including new Cummins KTA19-M3 rated at 530 hp continuous at 1800 RPM. The new engines were fitted in the enlarged engine cabinets that are located on the car deck in opposing corners. Their engine beds are raised to allow the ZF550 gears to turn directly into the existing Ulstein drives. The drive legs extend nine feet down through the deck. With the new engines the pitch of the 52-inch propellers was reduced from 38 to 35 inches. Engineer Robert Martin explains that the combination of the engine change and the change in the pitch gives the ferry good initial power as well as good response on the top end. Martin is also pleased with the new Cummins Northwest supplied digital display console in the wheelhouse for the detailed real time information that it gives as well as the history that it records for each engine including exhaust temperatures, percentage load, percentage throttle and turbo boost pressure.
The Guemes is the only ferry on the run, so reliability is important. With a new schedule, on a weekday it runs from 6:30 AM to 10:00 PM and weekends it runs until midnight. A round trip can take as little as 15 minutes and the ferry will keep going if cars are left from a scheduled trip. On a typical round trip in December, Capt. Monty Hughes demonstrated how with nearly two knots of ebb tide running across the face of the pier he adjusts the z-drives to bring the forward end of the ferry in under the vehicle ramp on the pier with great precision. “You couldn’t do this without z-drives,” he declares.
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