All three vessels are twin screw tugs built to the VT Halmatic WB18 design, configured primarily to transport and deploy floating protective pollution control booms while at the same time retaining the ability to operate as powerful and versatile workboats.

Un-named but numbered HCC-1001, HCC-1002 and HCC-1003, the vessels have a welded steel, double chine hull with an overall length of 19.00m, a maximum beam of 6.56m and an approximate draft in the full load condition of 2.00m. The vessels displace approximately 106 tons in the fully loaded condition and internal tanks can accommodate 19,500 litres of diesel fuel and 1,400 litres of fresh water.

Fabrication of the hull and all major steelwork was subcontracted by VT Halmatic to the Dutch shipyard Intervak Shipbuilding & Construction of Harlingen and carried out using pre-cut steel components produced in the Netherlands by Centraalstaal. This approach to the construction of steel vessels is now being used extensively by VT Halmatic to streamline production and reduce costs.

All three tugs arrived at nearby Portsmouth as deck cargo on one ship following a short delivery trip from the Netherlands. Fitting out and subsequent trials were undertaken by VT Halmatic's Portchester yard, making good use of its extensive indoor workshops and 'Syncho-lift'.

The hulls incorporate a semi-raised foredeck and the underwater hull form affords an uninterrupted water flow to the twin screw propulsion system. Bottom, side and transom plating is 10mm thick and a 20mm sheerstrake is located at gunwale level.

The deckhouse is an all steel structure, arranged on a single deck with a small, unprotected flying bridge. Moulded rubber bow fendering, supplied by Fendercare, has a large surface area and a central knee extending down to the waterline.

Additional fendering, in the form of neatly secured vehicle tyres, is provided around the sides and aft quarters.

Each vessel is powered by two Cummins KTA 19M3, 6 cylinder, turbo-charged and after cooled main engines, each rated at 600bhp (447 bkW) at 1,800rev/min MCR. Power is transmitted via Twin Disc MG5170-DC gearboxes to a pair of bronze Kaplan type four-blade propellers of 1,650mm diameter, rotating within fixed Kort Nozzles. The main engines are cooled by a fully enclosed keel cooling system and a dry exhaust system incorporates silencers mounted in the engineroom with outlets above the wheelhouse roof.

A pair of semi-balanced plate rudders with small 'fish-tails' are actuated by a Kobelt power-assisted steering system, with a single central wheel in the wheelhouse and a 'jog-lever' on the flying bridge console.

Helm indicators are fitted at . .

. . both control positions.

Manoeuvrability is enhanced by the installation of a hydraulically powered VT40 bow thruster, supplied by an associate division of VT Halmatic. The unit can be controlled from the wheelhouse and flying bridge and has a maximum rating of 45kW (60hp).

Hydraulic power for the steering gear, bow thruster, deck crane and boom reels is supplied by pumps driven direct from the main engines. On trials the vessels achieved a bollard pull of over 15 tons and a free running speed of 11 knots.

Onboard electrical power is supplied by a single Onan model 22.5 MDKAF diesel driven generator set with a continuous rating of 22.5kW at 1,500rev/min. The generator is located in the after end of the engineroom and enclosed in an acoustic cabinet. Controls and instrumentation for the set are situated in the wheelhouse along with electrical panels supplied by the E-Tech Group.

All three tugs have an identical deck layout with a large clear working space aft, a set of 'H' towing bitts and a deck crane situated immediately aft of the deckhouse. An important feature of the deck layout is the provision of securing pads for a Vikoma ISO 10ft x 10ft demountable container housing 250m of Vikoma Sentinel neoprene boom on a hydraulically powered reel. When the container is in position, it is surmounted by a cradle accommodating a 4.2m Rigid Inflatable Boat (RIB), powered by a 27hp diesel outboard motor. The boat is used as a boom tender, primarily for use in towing and positioning booms.

The Palfinger PK 10000, hydraulically powered 'knuckle boom' crane is equipped with a wire hoist and has sufficient reach and capacity to handle the RIB and assist with the boom and other equipment.

For this purpose the crane has a maximum lifting capacity, at the required outreach, of 3 tons.

Also installed on the vessel is an efficient 'hot wash' facility to enable the deck and pollution control equipment to be cleaned after use. The pressure washer to support this equipment is located in the engineroom.

Other deck equipment includes a Gemmell & Prout hydraulic windlass on the foredeck to handle the single 35kg 'Stokes' high holding power anchor and its 80m of short link chain, the usual mooring posts and life saving equipment. A chain locker located in the forepeak is fitted with a steel drainage box to prevent contact between the chain and hull structure. All three vessels are equipped for use as versatile workboats when the pollution control equipment is removed.

Lifesaving equipment includes a Jason's Cradle man-overboard recovery system, a 'Halmatic Matesaver' recovery pole and the usual mandatory items.

A spacious wheelhouse has a single control position at the forward end with good all-round vision for the tug master through a total of 12 windows. The forward windows are angled steeply outwards, giving the vessel a distinctive style.

An overhead window is provided on both sides at the forward end of the roof. Controls and instrumentation have been kept simple with the majority of engine and propulsion system instruments located on a central console at the control position.

Engine and gearbox controls are combined in a single twin-lever installation.

A navigation and communications equipment package includes a magnetic compass, Simrad radar, Furuno NX 500 Navtex and a JRC NWZ 4551 display unit. The Simrad navigation system comprises a single 10 inch TFT display with combined inputs from the radar, DGPS, chart-plotter and echosounder. A Sailor RT 4822 Marine VHF radio with DSC is installed at the control position, with a repeater on the flying bridge. The radio system provides a talkback system with speakers in the galley, forward store and on deck.

Accommodation below decks is fitted out to a high standard with a galley, a two berth cabin, sanitary spaces for WC and shower, and useful storage areas. The accommodation and wheelhouse are well insulated with mineral wool slabs or spray foam insulation and lined using materials and components from BD Systems.

Alto Mondopave flooring is used in the wheelhouse and access to the accommodation is by means of an internal companionway at the forward port side. The engineroom can also be accessed internally from the accommodation via a watertight door.