Special attention has been given to maintain a shallow draft and the ability to operate in short, steep, seas. Large bilge keels, a skeg and semi-raised foredeck are incorporated in the design with that requirement in mind.

The after deck has been kept as clear of obstructions as possible and the vessels are fendered all-round to enable them to tow ahead astern and alongside.

Two Caterpillar 3512B main engines running at 1800rev/min provide a maximum of 3345bhp (2x1231kW), to drive a pair of Schottel SRP 1010 FP fully steerable propulsion units.

This arrangement gives the tugs a bollard pull of 35 tonnes pulling ahead and 30 tonnes astern, and a free running speed of 12 knots.

Unusually for stern drive tugs, these vessels are intended to tow mainly over the stern from a quick release tow hook. Located in the bow is a sizeable set of forward towing bitts for use when working alongside or when assisting barges and other floating plant. A small hydraulic deck crane is fitted to assist with stores and towing gear. All five tugs are fitted for fire fighting with two monitors located on the wheelhouse roof.

A high level of automation enables the vessels to be operated in harbour with a crew of three.

Accommodation and suitable facilities are provided however for a maximum of eight persons whilst carrying out coastal tows or longer repositioning voyages.

The two mooring/line handling tugs are 17m in length overall, with a beam of 6m and depth of 2.5m (at main deck). These small ASD vessels have a low profile, with folding masts and guard-rails to prevent fouling while working with mooring lines. A pair of Caterpillar 3306B main engines produce a total of 652bhp (2 x 240kW), at 1800 rev/min. The engines are coupled to small, fully azimuthing, Schottel SRP 170FP propulsion units, to give the vessels a 6 tonnes bollard pull and great agility.