New ASD 39/70 Class offshore terminal support tug Independence for Boston Towing

November 27, 2009

Boston Towing and Transportation Company took delivery in early November, 2009 of the Independence, a unique new ASD 39/70 Class tug, designed by Robert Allan Ltd., Naval Architects of Vancouver, B.C., to serve the new Neptune LNG LLC, Deep Water Port, offshore Massachusetts Bay.

This tug is the larger of two new vessels intended for this operation. The new tug is configured for a wide range of duties including harbour towage and ship-handling, fire-fighting, coastal towing, salvage and rescue towing operations, however the primary role will be standing-by for tankers using the offshore mooring buoy, located in a fully exposed deep water location.

Principal particulars of the ASD 39/70 ASD tug are as follows:

Tank capacities are as follows:

The Independence was built at Derecktor Shipyards in Bridgeport, Connecticut, and is classed by ABS:

• ABS ✠ A1 Tug
• Fire-fighting Class 1
• International Loadline, USCG
• Marpol

This ASD 39/70 design is very similar to comparable RAstar Series tugs from this office, but due to its many unique features it has been given a more general ASD type designation. The tug features a full raised forecastle running nearly half the length of the tug which provides a very high standard of accommodation the ability to work in quite extreme sea-states and the best possible sea-keeping capability for operation in very exposed conditions.

The vessel is outfitted to the highest standards for a normal crew of up to eight people. The forecastle level deckhouse incorporates a spacious suite for the Master. The main deck accommodations include two Officer’s single cabins and two crew double cabins. There is also a fully-equipped modern galley and a spacious lounge/mess room. The wheelhouse is designed for maximum visibility with a single control station providing maximum visibility to both fore and aft deck working areas. The noise level throughout the crew accommodation is predicted to be in the range of 65-70 dBA, based on utilizing advanced methods of vibration isolating main propulsion machinery, as well as high grade insulations.

Main Propulsion for the ASD 39/70 comprises a pair of MTU 16V-4000 diesel engines, each rated 2000 kW at 1,800 rpm, each driving a Rolls-Royce model US 255 CP azimuthing Z-drive propeller. The controllable pitch Z-drives provide enhanced fuel economy, operational flexibility, and enable efficient operation of the main engine-driven fire-fighting system.

This drive combination is guaranteed to deliver a minimum Bollard Pull of 67 tonnes, and provide a free running speed of not less than 13.5 knots. By current standards the power is rather small for a tug of this size; however the latter was dictated by the demands to provide a high standard of comfort and sea-worthiness for the crews who will be on station in fully exposed North Atlantic sea conditions for up to two weeks at a time. The unique, sponsoned hull form, which this design has in common with the Robert Allan Ltd. RAstar Series tugs, provides roll amplitudes and roll accelerations less than half those of other recognized “standard” tug forms of equal size and displacement. These special design measures will provide the crew with a much safer work platform, and much better rest conditions.

Fire-fighting will be to a Fi-Fi 1 Class, with pumps driven by the main engines.

The main hawser winch forward is a single drum, Markey EEPC-52 model, containing 750′ of 10″ circumference synthetic hawser, with a brake capacity of 264 short tons. The aft towing winch is a Jonrie model 512 with a 2,500′ (760 metre) 2.25″ SWR for towing.

For more information on this unique high-performance tug, or on any of the design services offered by Robert Allan Ltd., please contact us.