The innovative ZeroCat 120 ferry owned by Norled and built by Fjellstrand, which won the Skipsreyven Ship of the Year industry award, features optimised Azipull thrusters from Rolls-Royce.
An important factor in the development of the ferry was to provide a propulsion system with the lowest possible energy consumption during fjord crossings, and at the same time ensure safe and efficient low speed manoeuvring when operating near piers. The propulsion system is a key element in lowering energy requirements, enabling a reasonably-sized battery pack to be installed on board. To achieve high energy efficiency, the system from Rolls-Royce has a low propeller rotation rate, propeller blades with high aspect ratio and a low blade area, and a slender thruster body. The battery technology and electrical systems are provided by Siemens.
The vessel has one thruster at each end of the catamaran’s hulls. The Azipull 085 thrusters are the first to have a propeller that can be adjusted to a fully feathering position. This means that the four propeller blades on the front Azipull thruster, which are not in use during the crossing, are adjusted to an angle that minimises resistance from the water flow. Hydraulic steering of thrusters has been replaced by electric steering to reduce energy consumption still further.
Leif Vartdal, Rolls-Royce section head for hydrodynamics in marine research and technology, said: “An efficient propeller has a large diameter that rotates at a low speed to turn engine power into thrust in an effective way. In this case we have achieved this because the Azipull units have a high torque transmitting capacity for the given power of the propulsion motors. The hull design also allows for a larger propeller diameter than is usually found in a double-ended ferry. The result is better propulsion efficiency and less power drained from the batteries.” MP