It replaces the azimuthing stern drive (ASD) tug Silex, now redeployed to Italy on charter, and joins the remaining ASD tug Thrax and two tug/workboats to provide virtually all the shiphandling, escort and line handling services at Fawley.

Completed by the Spanish shipyard Astilleros Gondan SA of Figueras, Asturias, Tenax is a powerful but compact Voith tractor tug designed to carry out tanker handling and escort duties, safely and efficiently. Robert Allan Ltd, Canadian naval architects and consultants, were responsible for the design, working in close cooperation with Ostensjo's technical consultant Carl J Amundsen.

Tenax is a vessel of 37m in length overall with a breadth of 14m, and operational draft of 6.7m. The tug has been constructed to meet the requirements of DNV +1A1 Tug, EO, OILREC, FiFi 1 Escort(130/10) ISM. The highly developed and unusual hull design incorporates a bulbous bow, sponsons and bilge keels and is optimised to operate effectively while moving ahead or astern and achieve very high steering forces when operating in the escort (indirect) towing mode.

The propulsion system installed in Tenax is a little different from its earlier sister ship Velox in that the Voith Schneider units are of the five-bladed 32R5/250-2 type (not six blades as in Velox) with the very latest type of longer blades.

An improved 'slotted' protection plate is also utilised. Power is supplied by two Rolls-Royce - Bergen C25:33L8P main engines producing a total of 6,850bhp (5040kW) at their maximum continuous rating of 1,000rev/ minute (slightly more than Velox).

A static bollard pull of 70 tons was achieved on trials along with a maximum free running speed of 15 knots. Maximum steering forces, while operating in the indirect towing mode at 10 knots, of 150 tons are anticipated and a similar figure for maximum braking forces.

Like her sister Tenax is also fitted with a 'Voith Turbo Fin' (VTF) intended to maximise 'lift' and provide very high steering forces when the tug is operating fin-first in the escort role. The deep vertical skeg has a rotating cylinder fitted within its leading edge (the leading edge when travelling 'skeg first') to improve boundary layer flow and provide a significant increase in 'lift'. Direction of rotation is critical and automatically adjusted to suit the tug's angle to the towline - to port or starboard.

A hydraulic motor of only 45kW powers the unit and the cylinder has a maximum rotational speed of 245rev/minute.

Electrical power is supplied by two identical Volvo-Penta TAMD74A auxiliary diesels driving Stamford 135kW alternators. Hydraulic pumps for the main deck machinery system and the fire pumps are coupled to the forward end of each main engine via Kumera-Norgear step-up gearboxes.

The towing equipment installed includes a hydraulically powered Karmoy towing winch with two large split drums on a common shaft with a maximum line pull of 200 tons and a 300 ton brake holding capacity.

Each drum is fitted with a high performance Steelite man-made fibre towline of 92mm diameter and 350m in length. One towline can be replaced by a 1,000m steel wire towline should it be required. The winch is operated from the wheelhouse and can be used to control the length of towline and the maximum load applied automatically, during escort operations.

A towing staple (fairlead) of unusual design is intended to accommodate both steel wire and a synthetic towline and aid stability in both escort and towing roles. Other deck equipment includes specially designed towing pins on the after bulwarks, a capstan and anchor windlass.

A hydraulically powered Effer 44000-3SL knuckle boom crane, complete with a winch and wire lifting mechanism is fitted on the starboard side of the winch fairlead, for use in handling stores, towing gear and deploying a skimmer.

Fire fighting equipment fitted to meet the FiFi 1 standards includes two Unitor monitors located at boat deck level. One monitor is capable of delivering 20,000 litres/minute and the other water/foam at the same rate. Two pumps driven by the main engines are rated at 1,500 m 3/hour to supply the monitors and the mandatory self protection spray system. Tenax carries equipment to dispense chemical dispersant, deploy a skimmer and a protective boom.

The skimmer is stowed below deck in the equipment store and the boom on a hydraulically powered reel located within the superstructure.

The wheelhouse affords excellent visibility when operating bow or skeg first and the controls are optimised to afford the tug master the best possible control position when operating in the escort mode where maximum concentration is required.

Navigational equipment includes two Furuno radars, a gyro-compass, auto-pilot, electronic charting, DGPS, an echosounder, log and Navtex.

The communications outfit meets the GMDSS and IMO standards for use in Sea Area A2.

The tug is fitted out to the highest standards for a crew of up to six persons in fully heated and air conditioned accommodation.

Six single cabins are provided and facilities include a spacious lounge/mess room, a modern fully equipped galley and a fitness room.