They will assist LNG tankers to and from a terminal in the Mystic River, Boston Harbour, and carry out barge handling work as a secondary duty. The vessels will be 28.04m in length, 9.75m beam, with a draft of 4.09m built to ABS class +A1, +AMS, with notation: Towing Service and Fire Fighting Capability. The tugs are typical of many shiphandling ASD vessels currently entering service with US operators.

Both tugs will be powered by two Caterpillar 3516B, electronic injection, main engines each generating 2200bhp at 1600rpm.

Power is transmitted to a pair of fully azimuthing Rolls Royce (Ulstein) 1650H propulsion units equipped with 2.18m diameter stainless steel propellers and nozzles with stainless steel liners. This propulsion system is expected to give the vessels a bollard pull of approximately 49 tons ahead and 47 tons astern.

Two Caterpillar 3304 powered auxiliary generators will each run at 1800rpm to provide 99kW at 120/208 volts, 3 phase. An additional 480 bhp Caterpillar 3406TA engine will power a centrifugal fire pump to supply a pair of 3000gal/min Alco monitors. Both main engines, fire pump engine and propulsion units will be keel cooled by grid coolers, and the generators will be cooled using the skeg as a cooler.

The towing gear includes two Markey electrically powered and controlled towing winches incorporating a constant-tension 'hands-free' render-recover system. A ship-handling winch in the bow will have a maximum brake load of 180 tons and line pull of 19 tons, and carry 150m of synthetic fibre towline.

A similar, two speed, winch fitted on the after deck will have a line pull of 70 tons and accommodate 640m of 50mm steel wire towline.

Navigation and communications equipment will include a Furuno GP-37 DGPS; a Robertson AP9MK3 autopilot; a Furuno SC-60 satellite compass; a Simrad RA53-4-24V radar with a 64nm range; a Furuno 1953 C/NT-4' scan radar; a Furuno RD-30 depth sounder; and two Standard Omni VHF radios.