New offshore terminal support tugs for Boston Towing from Robert Allan Ltd.

September 7, 2007

Boston Towing and Transportation Company have contracted with Robert Allan Ltd., Naval Architects of Vancouver, B.C., to design a pair of new offshore LNG Terminal Support tugs to provide the services required for The Neptune LNG LLC, Deep Water Port, offshore Massachusetts Bay. The larger of the new vessels, designated as an ASD 39/70 Class tug by Robert Allan Ltd., will be the first of its kind built and operated in North America, although there are numerous other RAL-designed tugs, including many of the similar RAstar Series tugs currently building worldwide for major oil and LNG terminals. The second vessel will be a modified RAmparts 3000 Class tug, which will primarily be engaged in harbour duties, but will serve as the back-up vessel for the larger tug during service periods.

The new tugs will be suitable 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 tankers using the offshore mooring buoy.


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


Length Overall
Beam, Moulded
Depth, Moulded
Maximum Draft (overall)
Gross Tonnage
Potable water capacity
– 128′-4″ (39.10 metres)
– 44′-4″ (13.50 metres)
– 19′-5″ ( 5.92 metres)
– 18′-10″ ( 5.75 metres)
– < 300 GRT (US)
– 5.2 cubic metres


Tank capacities are as follows:


Fuel Oil
Potable Water
Water Ballast
Lube Oil
Hydraulic Oil
Waste Oil
Oily Water
Sewage Tank
US Gallons
– 66,500
– 10,000
– 88,500
– 1,750
– 600
– 1,400
– 1,240
– 1,300
Cubic Metres
– 251.6
– 38.0
– 335.0
– 6.6
– 2.3
– 5.3
– 4.7
– 4.9


Both vessels will be built at Derecktor Shipyards in Bridgeport, Connecticut, and will be classed by ABS:


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


The ASD 39/70 design features a full raised forecastle running nearly half the length of the tug to provide a high standard of accommodation and the best possible sea-keeping capability for operation in exposed conditions. The general layout of the tug is illustrated in the General Arrangement drawing:



The vessel will be outfitted to the highest standards for a normal crew of up to eight people. The forecastle level deckhouse includes a spacious suite for the Master. The main deck accommodations include two single Officer’s cabins (each with spare bunks) with a shared en-suite facility, and two double crew 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.

The Z-drives are bolt-in style, arranged for removal afloat.

This 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.

The electrical plant is comprised of two identical diesel gen-sets, each with a 120/208 volt/60 Hz power output of 99 kW.

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

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.

Ship-handling fenders comprise an 800 mm cylindrical fender above a row of 450 mm “W” block fenders. A 300 x 300 hollow “D” fender provides protection at the main and foc’sle deck sheer lines, and “W” block type fendering is used again at the stern.

The RAmparts 3000 tug will be similar to the many of that popular tug Series already in International service. The main difference between this tug and its predecessors however will be the inclusion of a JAK-400 type push-pin system for ATB barge operations.

The propulsion plant for the 30 metre tug will be virtually identical to the ASD 39/70, providing a very powerful, compact, and multi-functional vessel.

The first tug is scheduled for delivery in January, 2009. The smaller vessel will follow approximately four months later.

For more information on any of our high-performance terminal support or escort tug designs, please contact us.