A Mini-Tractor for the US Navy

Moduteh Marine, of Tacoma, Wash., has gained recognition on meeting the stringent conditions of military contracts. In 2020 they completed a contract to build a fleet of five small tugs. These carry the military designation Work Boat Docking.

“The mission of the CNIC Work Boat Docking (WB Docking) is to provide waterborne support at U.S. Navy Installations,” said Modutech’s Brian Swindahl. “The boats are required to have the ability to safely assist vessels including submarines for mooring and dry-docking, open and close security barriers, as well as to tow/push floating port operations support equipment. The boats must include propulsion equipment that is optimized for bollard pull, be highly maneuverable, and include sufficient deck fittings and winches to tow astern, alongside, or push.”

In effect, the Navy wanted a Swiss Army knife that would fit in a mooring pocket. Modutech built a series of five boats that do just that. The rectangular shaped 25- by 14-foot hulls have an 8-foot draft. The relatively deep draft results from the requirement that these little boats be highly maneuverable. To meet that requirement, they are fitted with s single Schottel SRP 150 azimuthing drive. The drive has a 41.3-inch propeller in a nozzle. The forward-mounted drive is protected by a heavy pipe guard. A pair of fins, with approximately the same depth as the single drive, enhance the maneuverability while providing tracking stability.

The powerful heart of these remarkable craft is a single Cummins QSM11 engine, producing 450 horsepower at 2,100 rpm. This big power gives the little tug a speed over 7.5 knots and a bollard-pull in excess of 10,000 pounds. This power allows the tug to operate in both push and towing methods as required.

The steel hull carries an aluminum pilot house with heating and air conditioning. The wheelhouse can be removed for repair or transportation. Similarly, a pair of push knees mounted forward are removable. Arching from the top of the push knees, over the house, and down to the aft deck, a cage allows the boat to pass easily under mooring lines. Normal operation will be with a two-person crew, although there is room for an additional five passengers.

The five Cummins-powered Yard Tugs were deployed to naval yards in 2020.

(Photo: Alan Haig-Brown)