VESSEL REVIEW | Mini-tugs to provide docking support for US Navy ships and submarines

Modutech Marine of Tacoma, Washington has completed construction of five small tugs in a series for use by the US Navy in providing docking and undocking support for its surface ships and submarines.

Known by their official navy designation of Commander, Naval Installation Command Work Boat Docking (CNIC WB Docking), the tugs were designed to have the ability to safely assist vessels for mooring and dry-docking, to open and close security barriers, as well as to tow and push floating port operations support equipment. The boats were also built to be highly manoeuvrable and possess propulsion equipment that is optimised for bollard pull, in addition to featuring sufficient deck fittings and winches to tow astern, alongside, or push.

Since Modutech has had prior experience supplying the navy with a range of docking/undocking vessels, from 30-foot (nine-metre) pocket workboats to more powerful 60-foot (18-metre) harbour tugs equipped with Z-drives, the development work on the new craft became easily aligned with the service’s requirements.

Modutech supplied the navy with five rectangular-shaped craft that each have a length of 25 feet (7.62 metres), a beam of 14 feet (4.27 metres), and a draught of eight feet (2.4 metres).

The relatively deep draught results from the requirement that these workboats be highly manoeuvrable, enabling them to better assist large navy vessels during docking/undocking especially in close quarters. To meet that requirement, they are each fitted with a single Schottel SRP 150 azimuthing drive with a 41.3-inch (105-centimetre) propeller housed in a nozzle.

The drive is forward-mounted and is protected by a heavy pipe guard. A pair of fins, with approximately the same depth as the single drive, enhance the manoeuvrability while providing tracking stability.

The tugs are each powered by a Cummins QSM11 main diesel engine that produces 450 hp (335 kW) at 2,100 rpm. This configuration delivers a speed of just over 7.5 knots and a bollard pull in excess of five tons (4.5 tonnes). This power also allows the tug to operate in both push and towing methods as required.

The steel hull carries an aluminium pilot house with a Furuno radar, small upward-facing windows, as well as heating and air conditioning. The wheelhouse is designed to be removed for repair or transportation. Similarly, a pair of push knees mounted forward may be removed to allow maintenance to be performed.

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 without getting snagged.

Normal operation will be with a crew of two, though there is room on each vessel for an additional five passengers.

The five CNIC WB Docking tugs were delivered by Modutech to the navy beginning in 2020. All have since been deployed to the service’s various installations.

See more stories from this month’s Tug and Salvage Week here.