Experience of Azipod Vessels in Ice

In late 1980’s, ABB and Masa-Yards (former Wärtsilä Marine) started the development of azimuth thrusters where the electric drive motor would be in the hub of the thruster. Finally in 1990, ABB and Masa- Yards carried out the pilot installation on buoy tender Seili. The mechanical CPP arrangement was replaced by an Azipod thruster unit and also the main engines were renewed. Since then some 15 icebreaking ships of different kinds have been retrofitted or built with the new revolutionary device. During the further development it was found that the vessels equipped with azimuthing thrusters were able to operate running astern better than before, even better than running ahead. This patented innovation was later developed further for various applications. One of these is the idea of Double Acting Ship (DAS). The principle idea of a DAS is to optimize the vessel into different conditions. For instance MT Tempera (106,000 DWT) is designed to operate in ice running astern and the bow has been optimized for open water. This way the inefficiency (20-40% less efficient in open water) of a typical icebreaking vessel with an icebreaking bow is removed and the vessel can be cost effective in all conditions. This paper describes the development phases of the Azipod device and discusses the full-scale experience of the vessels built. In winter 2006 the two latest installations, Fesco Sakhalin and Norilskiy Nickel, have been tested by Aker Arctic Technology in real operational conditions. Also the experience from these two is discussed. The most recent vessels have onboard a long-term monitoring system for loads on the pod.