Innovative Anchor Handling Vessel

Bourbon Offshore Norway has been a prime mover in developing, together with Ulstein Design AS, a new ULSTEIN AX104 anchor handling vessel. The vessel stands out due to its three innovative features - inverted bow design, diesel electric propulsion, and the introduction of a new safe anchor handling system. The shape of the hull has been optimised for high speeds, low resistance and low fuel consumption. Improved stability in extreme weather conditions is expected to benefit crew’s comfort and safety during work and rest periods.

The new vessel has no bulb, and has a slender bow design ULSTEIN X-BOW™ with an inverted flare. The bow slopes backwards instead of forwards which results in less resistance. Some of the most common accidents that occur on offshore vessels involve the sea breaking the wheelhouse’s windows. This happens because traditional hull shapes throw the sea forwards and upwards as the hull dives deeper. The tests on the model showed that almost no sea came up onto the bridge deck at all, even in extreme weather conditions with six metres significant wave height and a wave period of nine seconds. Under these conditions, the model maintained a good service speed. The large volume in the bow means that the forebody floats better and dives less when it meets waves.

This means that no slamming occurs and the hull moves through the sea very gently, according to the vessel designers. Even high and choppy waves did not result in sea spray on the bridge deck, which means that the likelihood of extreme weather damage to the forebody will be reduced. Since the smooth forepart goes all the way up to the bridge deck, this means that better protection is afforded for all the deck equipment, which is typically exposed to the wind, weather, and icing.

The vessel, 83.6m long with 18.5m beam, is capable of a speed of 17.5 knots and will be one of the world's first AHTS vessels with diesel-electric propulsion. It will be equipped with six Wärtsilä generating sets having a combined electrical output of 14,850 kW supplying propulsion and manoeuvring system comprising of Lips thrusters. The main steerable thrusters, each with a power of 5,000 kW, will have controllable-pitch (CP) propellers 3.6m diameter running in Lips HR nozzles. The 1800 kW bow steerable thruster will be equipped with a 2.4m-diameter CP propeller, while the 1200 kW bow tunnel thruster will have a 2.5m-diameter CP propeller. The vessel is fitted with DP2 dynamic positioning system.