New Navy z-drive tugs exhibit power and finesse

Change has visited itself upon Navy Region Northwest. It comes in the form of purpose-built Z-Tech azimuthing stern drive tugs to service the aircraft carriers, submarines, naval vessels and barges in their Puget Sound operations at Bremerton, Bangor and Everett.

The azimuthing stern drive tug, designed by Robert Allan Ltd., assists the U.S. Navy aircraft carrier John C. Stennis at the Puget Sound Naval Shipyard in Bremerton, Wash. Three of the tugs have been delivered to the Navy and a fourth is under construction. (Brian Gauvin photos)

Three of the tugs, Valiant (YT 802), Reliant (YT 803) and Defiant (YT 804) have been delivered by J.M. Martinac Shipbuilding in Tacoma, Wash. The yard has extensive experience building Z-Tech tugs, designed by Robert Allan Ltd., in Vancouver, British Columbia. A fourth tug is under construction.

The crews are civilian, one result of a shift to a civilian-style tugboat operation that began in the mid 1990s. Pacific Tugboat Service, of San Diego, is the prime contractor for constructing the tugs.

Each of the 3,620-hp tugs is powered by a pair of Caterpillar 3512C main engines rated at 1,810 hp each at 1,600 rpm. The z-drives are Schottel SRP 1012 units with 83-inch propellers. A bollard pull of 38 tons was expected, but Valiant registered 42 tons of pull forward and 44 tons astern on trials. Experience at the Martinac yard has shown that the extra bollard pull is not unusual in the characteristics of Z-Tech hull design.

According to Jay Anderson, port captain for the Northwest Navy Region, the Navy chose to modify and tone down the 60 tons of bollard pull produced by the Z-Tech 6000 design to suit the navy’s broad range of requirements. The result is the Z-Tech 4500 class.

“We needed a tug that could handle the aircraft carriers, but also one to which we could apply a finer touch,†said Anderson. “We push the limits of the tug with the carriers, but we need to be able to fine-tune our maneuvers for the smaller boats and the barges. So we didn’t want too much horsepower jerking us around.â€

“The boats are working very well for what they were designed to do,†he added, “and they have outstanding creature comforts.â€

Capt. David Jones commands Valiant (YT 802), which boasts a bollard pull of 42 tons.
Chief Engineer Randy Garner in the engine room.
One of the two Caterpillar 3512C main engines rated at 1,810 hp each at 1,600 rpm.
The Caterpillar-powered Schottel SRP 1012 z-drives with 83-inch propellers.
Although the tugs work with military vessels, they have civilian crews as a result of a shift to a civilian tug operation that began in the 1990s.
Valiant’s crew, from left to right: Chief Engineer Randy Garner, First Mate Randy Junell, Capt. David Jones and deck hand Greg Bryan.
Bryan and Junell bring in a line from the aircraft carrier. Valiant and its sister tugs handle Navy vessels ranging in size from aircraft carriers to barges, operating from Bremerton, Bangor and Everett.
By Professional Mariner Staff