US-based Modutech Marine has completed a contract to build a fleet of five small tugs to the military designation Work Boat Docking for the US Navy’s Naval Installation Command (CNIC)
Five of these Cummins-powered workboats were deployed to naval yards in 2020 to escort surface vessels and submarines into drydocks and quaysides.
“The mission of the CNIC Work Boat Docking vessels is to provide waterborne support at US Navy installations,” said Modutech chief executive Brian Swindahl.
“The boats are required to have the ability to safely assist vessels including submarines for mooring and drydocking; to open and close security barriers; as well as to tow and push floating port operations-support equipment.”
Modutech built these five vessels in a rectangular shape with 7.6 m length, 4.3 m width and 2.4 m draught. This may be shallow for harbour tugs, but still enables the vessels to be highly manoeuvrable, the builder said.
“The boats must include propulsion equipment that is optimised for the bollard pull, be highly manoeuvrable and include sufficient deck fittings and winches to tow astern, work alongside or to push,” said Mr Swindahl.
These tugs have a top speed of more than 7.5 knots, bollard pull of 4.5 tonnes and a single Cummins QSM11 engine, producing 335 kW at 2,100rpm. This engine drives a single Schottel SRP 150 azimuthing drive, including a propeller with a 105 cm diameter 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, enhances the manoeuvrability and provides tracking stability allowing the tugboats to operate in both push and towing methods as required.
The steel hull carries an aluminium 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.
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