All six meet the requirements of Germanischer Lloyd +100 A5 TUG +MC, AUT and are virtually identical in design, designated locally UNV 352 SD.

The tugs are 23.8m in length overall, with a 11m beam, a maximum draft of 5.0m and measure 236gt. Integral tanks accommodate 51.6m 3of fuel, 6.0m 3of fresh water and 4.0m 3of fire fighting foam. Below decks the hull is subdivided into five main compartments, the aft peak, propulsion unit compartment, engineroom, forward accommodation and fore peak. Watertight doors are provided in the main bulkheads at either end of the engineroom.

The hull is a robust all welded structure incorporating a deep box keel and an underwater shape typical of many RAL designs - offering exceptional manoeuvrability and stern-first performance. Extensive cylindrical fendering is provided at the bow and stern with 'D' section mouldings at the sides. The bulwarks are heavily stepped-in for clearance and safety. A single anchor is located in a 'pocket' below the stern and handled by a small Hatlapa windlass just inside the after bulwarks.

The tugs are powered by two Caterpillar 3516B main engines running at 1600rev/min to generate a total of 4255bhp (2 x 1566kW) to power a pair of Schottel SRP 1212 CP fully azimuthing propulsion units.

Each Schottel unit embodies a high performance nozzle and controllable pitch propeller.

The latter gives precise control at all speeds and eliminates the need for slipping clutch units.

Connection between each engine and propulsion unit is via a flexible coupling and cardan shaft, with a seal incorporated where the shaft passes through the watertight bulkhead. Main and auxiliary engine cooling is by means of Bloksma box coolers located on either side of the engineroom.

On trials the tugs exceeded the specified performance figures requiring a bollard pull of 53 tonnes while towing ahead and 48 tonnes astern, with a free running speed of 12.5 knots.

Electrical power aboard the tugs is supplied by two diesel powered generator sets located in the centre of the engineroom.

Each set comprises a Caterpillar 3054 engine running at 1800 rev/min, coupled to an alternator rated at 90kVA, 440v - 60Hz.

A single Kvaerner fire pump of 800m 3/hr capacity, driven by the starboard main engine, supplies the external fire fighting system. The latter includes two Kvaerner water-foam monitors positioned on a platform above the wheelhouse.

All of the tugs in this series tow mainly over the bow from a hydraulic powered Hatlapa single drum towing winch with a brake holding load of 137.5 tonnes and recovery speed of 30m/min at 5 tonnes. The drum carries an 80mm diameter manmade fibre towline of 150m in length with a 20m steel wire pendant. Power for the winch is supplied by two hydraulic pumps, one driven by each propeller shaft. The foredeck, considering the small size of the vessel, is spacious and the working area has been kept as free of obstructions as possible. Two Oelkes-Eichler quick release tow hooks are also provided, each with a safe working load of 65 tonnes. One is mounted adjacent to the winch and the other on a single towing bollard aft.

The wheelhouse is of typical RAL design, with good all round visibility and all of the essential controls grouped on a central 'U' shaped console. Navigational equipment includes two JRC radars, with maximum ranges of 64 and 96 miles, a JRC GPS, a Navitron NT-912G auto-pilot, a graphic echosounder and a Unilux magnetic compass. The communications outfit complies with GMDSS Areas 1 - 2 and includes two Skanti VHF radios and handheld portable VHF set by Jotron.

Unlike most compact tugs, where small size and low manning are a priority, these vessels have been fitted out to accommodate a crew of up to seven persons in fully air-conditioned quarters.

One single and three double berth cabins are located below decks, forward of the engineroom, and the galley, mess room and sanitary facilities in the superstructure.