Tractor Tugs Are the Answer

By Commander John Baucom, U.S. Naval Reserve

"They are fantastic," said Captain Jim Nolan, a retired pilot (and avid Merchant Marine Naval Reservist) who put one of Bay and Delta Corporation's new tugs through its paces a few years ago. "They are the greatest invention since macadamized roads." Bay and Delta Corporation now owns two 4,200-horsepower tractor tugs, the Delta Billy and the Delta Deanne. The major West Coast towing companies already have tractor tugs in their fleets to fulfill the OPA-90 and state escort requirements when handling tankers. Foss Maritime is working with Sea-River (Exxon) in the San Francisco Bay by providing a cycloidal tractor tug to augment the conventional tugs to maneuver the loaded tankers traversing the harbor and channels en route to the Exxon refinery at Benicia. Foss also has taken delivery of two escort tugs using the tractor tug technology-the Garth Foss and the Lindsey Foss, which cost $11 million apiece. Crowley Maritime, owner of one of the largest offshore fleets in the world, has eight tractor tugs on order.

Tractor tugs in the United States are becoming popular outside of the oil escort business as well. Bay Transportation Corporation (St. Philip Towing) in Tampa, Florida, has added two 3,200-horsepower Z-drive tractor tugs to its fleet, which assists in docking and undocking phosphate bulk carriers in Tampa Bay. It bought tractor tugs in 1988-a year before the Exxon Valdez oil spill. James Brantner, vice president of operations for Bay Transportation, said that the highly maneuverable vessels have reduced the number of tugs required for docking operations. The company is building a 6,700-horsepower tractor tug for the tanker and non-tanker escort business in Tampa Bay. Atlantic Marine, whose shipyard is near Mayport Naval Station on Florida's East Coast, has been awarded a $6 million contract by Hvide Marine, Inc., for a tractor tug that will be used for guiding tankers through environmentally sensitive Port Everglades.

Edison Chouest Offshore Corporation operates four 4,000-horsepower tractor tugs in Kings Bay, Georgia; one 4,000horsepower tractor tug in Mayport, Florida; and six 2,600-horsepower tractor tugs in San Diego, California. The reader may note some differences in the profile of the East Coast tugs and the West Coast tugs-there is good reason for this. The tugs working in Kings Bay and Mayport are fendered and designed for docking and undocking submarines, while the smaller and more narrowly configured West Coast boats can fit under the sponsons and overhangs of a man-of-war.

What distinguishes this new generation of high-technology tugs from conventional tugs is the ability to steer when maneuvering astern, and to maintain position when backing without having to rely on a stern line or quarter line to stay in shape. The tugs have undiminished backing power, and are more efficient as pulling units.

Tractor tugs are steered directly by their propellers rather than using rudders to direct the propeller wash. Several different methods are used to power these tugs. The most common ones in Europe are the Voit-Schneider, which utilizes a cycloidal propeller-a number of air-foil shaped vanes that rotate around a vertical axis-and the Schottel drive, which employs a conventional propeller (usually fitted with a nozzle) driven by a right-angle drive from a vertical shaft much like an outboard motor. The propeller can be turned through an arc of 360°to provide steering and reversing.

Several other systems are similar to the Schottel drive-the Z drive and the Harbor Master units both manufactured by Murry and Tregarthen in the United States are good examples; Ulstein also manufactures drives. Propeller-steered tugs, whether single or twin screw, usually fall into one of two configurations: pusher tugs whose propellers are located aft or the newer tractor tugs.

The tractor tugs are designed for pulling and are much less likely to capsize than conventional tugs when doing ship work on a tow line because of the forward propeller location.

They work equally well going ahead or astern, and usually work stern-first when required to push against a ship. A single deckhand can send the line over to the ship and then safely get away from the tensioned line. This is possible because the line is tensioned by the tug operator inside the wheelhouse. Because they are so maneuverable, the new tractor tugs need only one line in place. In addition, they can dispense with deckhands standing by on the ship or on the tug during maneuvering evolutions because, once a line is in place, there is no need to shift it when turning the vessel around as with conventional tugs. All of this means that deckhands are exposed less to the dangers of line snap-back.

In terms of labor efficiency, the new tractor tugs can operate with a crew of three or four, as opposed to the four-tosix crewmen on conventional commercial tugs, or the crews of ten-to-twelve on Navy YTBs.

Considering all factors, tractor tugs would be a worthwhile investment for the Navy.

 

 
 

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