Brunvoll active in offshore sector

Equipment & Technology - March 6, 2000

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Norwegian thruster manufacturer Brunvoll AS is enjoying a high level of orders for retractable and conventional tunnel thrusters for a variety of newbuildings such as shuttle tankers, cable layers, and large offshore support vessels.

Retractable thrusters continue to be particularly popular in the offshore market, says Terje Dyrseth, Brunvoll's Marketing Director, notable examples being thrusters of this type for shuttle tankers and for a new class of Anchor-Handling Tug-Supply (AHTS) ships for B&N in Sweden and Viking Supply Ships (see elsewhere in this issue).

Brunvoll thrusters have been specified for several shuttle tankers and other larger offshore vessels, the most recent of which is a new shuttle tanker for shipowners Berjshav and Navion in Norway ordered from Samsung in Korea. This particular newbuildingwill be equipped with a single 2,200kW retractable azimuthing thruster and two conventional tunnel thrusters, one in the bow and one in the stern.

The order follows similar contracts for retractable thrusters for First Olsen's Knock Whillan and Knock Sallie, and Navion's Navion Britannia, one of a series of five shuttle tankers built in Spain, which also has a suite of retractable and tunnel thrusters.

Fitting a shuttle tanker a retractable thruster helps to eliminate a problem often encountered by shuttle tankers when they are in ballast condition in bad weather.

In this state, rolling motions can cause conventional tunnel thrusters to draw air if they break the surface and, if bad weather is prolonged, ships fitted only with conventional tunnel thrusters may be prevented from loading.

This problem is overcome, however, when the retractable thruster is lowered beneath the ship. As Terje Dyrseth explains, a bow azimuthing thruster can also be used as a secondary propulsion unit, in order to achieve higher DP class on a single screw ship.

Swedish shipowner Bylock & Nordsjofrakt (B&N) and Norwegian offshore shipping company Viking Supply Ships will take delivery of the first of the new AHTS ships early this year. These innovative vessels are designed to spend part of the year engaged not as supply ships but as icebreakers on behalf of the Swedish Maritime Administration.

Based on the Kvaerner Maritime (KMAR) 404 design with increased cargo carrying capacity, the newbuildings are primarily intended for operations in the North Sea in the roles usually assigned to an AHTS.

However, every winter the Swedish Maritime Administration will have a three-month option on the ships, which are being built to DNV 'Icebreaker Class 10' standard.

Given the arduous nature of the icebreaking role of the new vessels, the design and construction of the thrusters required careful consideration. As Terje Dyrseth explains, Brunvoll is equipping these unique AHTS vessels with a pair of 895kW tunnel thrusters, one forward and one aft, and a 895kW retractable, azimuthing thruster forward.

The thrusters are only intended for use during conventional AHTS duties, and not during icebreaking, but had to be modified to withstand the loads encountered in ice, and the plate, which encloses the retractable when it is withdrawn, has been heavily strengthened.

Due to be delivered by the end of February, the first of the trio of newbuildings will be followed into service by numbers 02 and 03 in the series in the third quarter of 2000 and the first quarter of 2001.

Another unique project for which Brunvoll thrusters have been specified is a conversion now underway at Orskov shipyard in Denmark, where a car ferry formerly engaged on the Storebelt route is being converted into a cable layer for Danish Telecom.

The conversion of the Heimdal is due to be completed shortly. Brunvoll has supplied a 1,492kW retractable azimuthing thruster and a conventional tunnel thruster.

Having built the thruster units, Brunvoll installed the azimuthing thruster in a hull section that it is also fabricating, test the entire unit, and deliver the hull section to the yard ready for installation.

The Polar Prince, the first of a pair of multi-purpose subsea support/ROV vessels for Rieber Shipping AS built at Flekkefjord Slipp & Maskinfabrikk of Flekkefjord in Norway, is another example of a Brunvoll-equipped vessel.

Recently completed by the Norwegian yard, the Polar Prince is now engaged in service on telecom repair and burial work for Tico, West of Shetland, under a five-year charter to Sonsub.

Polar Prince is equipped with three thrusters forward - a pair of Brunvoll conventional tunnel thrusters, one of 1,125kW and one of 800kW, and a retractable azimuthing thruster rated at 1,500kW - plus an 800kW retractable azimuthing thruster and 800kW conventional tunnel thruster mounted aft.

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