Ostensjo Builds Sophisticated New Escort Tug

Norske Hydro has extended its contract with Ostensjo to supply towage and escort services at Sture terminal until 2009. Construction of the new vessel is underway at the Spanish yard of Astilleros Gondan SA with delivery expected towards the end of 2004, when the tug will replace one of the existing vessels at Sture, Audax or Vivax.

The new vessel will be a sophisticated tanker-handling/ escort tug designed by Canadian naval architect Robert Allan Ltd in close co-operation with Ostensjo’s technical consultant Carl J Amundsen. Incorporated in the design are many of the features found in the larger and highly successful escort tug Ajax introduced by Ostensjo in 2000.

A vessel of 37m in length overall, with a waterline length of 33.85m and beam of 13.1m, the tug will meet the demanding requirements of DNV +1A1 Tug, EO, OILREC, FiFi 1 Escort (140/10). The highly developed underwater design incorporates a bulbous bow, bilge keels and has been optimised to operate effectively while moving ahead or astern. A ‘Voith Turbo Fin’ (VTF), specially developed in conjunction the Ostensjo, will be fitted in a new revised skeg design to increase steering forces in the indirect towing mode.

Voith claim an increase in steering forces of over 20 per cent by fitting VTF, a rotating cylinder in the leading edge of the skeg (the leading edge when travelling ‘skeg first’) providing a much improved boundary layer flow and a resulting increase in ‘lift’. Direction of rotation is critical and is automatically adjusted to suit the tug’s angle to the towline – to port or starboard.

This will be the first installation of a Voith Turbo Fin in a full size vessel.

Two Rolls-Royce – Bergen Diesels model C25:33L8P, rated at 2400kW each, will power a pair of six-bladed Voith Schneider 32R6/210 propulsion units of a new design. The units will have blades with a new profile incorporating endplates, designed to improve efficiency and reduce noise and cavitation.

A static bollard pull of 65 tonnes is anticipated and maximum steering forces while operating in the indirect towing mode in the order of 150 to 160 tonnes.

A high free-running speed, an essential requirement in the escort role, of 15 knots is also specified.

Towing equipment will be installed to enable the tug to carry out escort operations, shiphandling and rescue towing.

A semi-enclosed Karmoy Winch AS with a split drum carry two 250m rope/steellite towlines or two 250m rope towlines for escorting and shiphandling, and a 1000m steel wire towline for sea work. A new design of towing fairlead will be used, to reduce towline damage during indirect towing and a secondary tow point aft will utilise specially designed towing pins of the same type as Ajax.

Fire fighting equipment will be fitted to FiFi 1 standards and pollution control facilities will include the spray booms and a skimmer. A 250m long protective oil boom will be accommodated in an enclosed housing along with a heavy-duty oil skimmer.

Ostensjo Rederi AS and their subsidiaries operate tanker handling and escort tugs at oil terminals in Norway, Great Britain and Ireland, and are major players in offshore support and ROV operations.