Ulstein Verft AS contracted in 2005 Bourbon Offshore Norway to build the ULSTEIN AX104 anchor handling vessel with the distinctive ULSTEIN X-BOW™ from Ulstein Design AS. ULSTEIN AX104 stands out due to its three innovations: diesel-electric propulsion, inverted bow design and the introduction of a new safe anchor handling system. ULSTEIN AX104 is one of the first anchor handling vessels (AHTS) in the world with diesel-electric propulsion. This vessel is equipped with Wärtsilä main engines and Wärtsilä thrusters: two Wärtsilä 9L20 and four Wärtsilä 6L32 engines, plus two LIPS CS3500/3500WN main steerable thrusters, one LIPS CS250/MNR retractable thruster and one LIPS CT250M-D tunnel thruster.

The anchor handling vessel is 83.6 metres long and has a beam of 18.5 metres. It is equipped with a 400-tonne winch, DP2 (dynamic positioning) and a minimum bollard pull of 180 tonnes. The vessel is outfitted for 35 people in one- and two-man cabins. 

Wärtsilä solution
The Wärtsilä medium-speed main engines deliver a total mechanical power of 14,850 kW to the six main generators in the machine room. These generators deliver the electrical power to the main switchboard from where it is transformed to the users – the main steerable, retractable and tunnel thrusters and also for hotel accommodation. All thrusters are provided with Wärtsilä controllable pitch propellers and are driven by frequency-controlled electric drives. This configuration offers a very flexible way of loading the main engines, resulting in lower lifecycle costs. The controllable pitch propellers driven by the frequency-controlled electric drives give the vessel increased manoeuvrability and low noise levels due to their low rotational speeds. With conventional propulsion all the machinery is running all the time, while with diesel-electric propulsion only the power needed is extracted.

Two Wärtsilä CS3500/3500WN main steerable thrusters of weld-in design with 3600 mm Wärtsilä controllable pitch propellers and LIPS HR nozzles in the aft ship are driven by a frequency-controlled electric drive of 3 MW in parallel with a 2 MW electric drive running at constant speed. This configuration makes it possible to control the propeller rotational speed between almost zero and 180 rpm at a maximum power of 3 MW. Between an electrical power of 3 and 5 MW the propeller speed is 180 rpm. The controllable pitch propellers are operated as optimized fixed pitch propellers for reasons of efficiency and noise.

One LIPS CS250/MNR retractable thruster with 2400 mm controllable pitch propeller and 19A nozzle in the fore ship driven by a frequency-controlled electric drive of 1800 kW is used for manoeuvring, dynamic positioning and additional bollard pull. This thruster will be deployed only when necessary and the depth under the vessel’s baseline allows.