Operating in ice requires a very special type of vessel and in turn those vessels require a special type of propulsion, as described by Dag Pike.Years ago the Russians solved the problem by sheer power with their nuclear powered icebreakers, but modern vessels designed for ice operations use more subtle forms of propulsion. Very good manoeuvrability is an essential criterion and now, instead of protecting propellers from the ice, the propellers are actually used to help break up the ice.
Arctech Helsinki Shipyard, which is owned by STX Finland and the Russian United Shipbuilding Corporation, has built a number of vessels for ice operations that are designed around these new techniques. The company designed and built the world's first commercial cargo vessel that can operate year-round in Siberian waters without icebreaker assistance. This 169.5m ship uses electric pod drives for propulsion and it can make 3 knots in 1.5m thick ice. With 13,000kW of power it can operate stern first into ice with the stainless steel propellers actually cutting through the ice.
Today Arctech is building two ships, the Sakhalin and the Arcticborg that employ the latest in icebreaking propulsion systems. The Sakhalin is a 100m long ice-breaking supply ship to work in the Sakhalin offshore oil fields. Like the cargo ship, she has 13,000kW of power and azimuthing pod drives that allow year round operations, fulfilling roles such as stand by vessel, tug, ice-breaker and supply vessel. Capable of operating in temperatures as low as -35°C she will operate in 1.7m thick level ice and penetrate 20m deep ice ridges. The power comes from four generating sets that supply power to a pair of azimuthing podded rudder propellers.The Arctecborg is one of two vessels being built for the Russian Ministry of Transport, and her role will be primarily ice-breaking at sea and in harbours. But she is also a rescue vessel that can go to the aid of vessels in trouble in the ice and she is equipped to deal with oil spills. With a length of 76m, the Arcticborg has 9MW of power installed and this is shared between two SteerProp thrusters at the stern and one in the bow. This configuration will allow her to operate in a patented oblique mode where she will cut a channel in the ice up to 50m wide. The engines driving the generators are capable of operating on low sulphur fuel.
These rescue vessels for the Russian Ministry are designed to provide the necessary back up to regular cargo ship operations on the Northern Route. Whilst the sea ice is reducing in these areas in recent years, there is still a measure of unpredictability about the conditions. The rescue vessels can operate in combination with existing nuclear ice-breakers to help keep routes open if the conditions should change during the time a ship is on passage. Diesel electric power is the chosen system for modern ice-breakers because it offers flexibility in how the power is applied, but also because it offers high torque at low revolutions. ABB developed the Azipod propulsion units specifically for this task because they allow a vessel to manoeuvre stern first in the ice without a vulnerable rudder. Operating stern first helps to flush the ice away and also lubricates the hull. The Azipod units have full 360° steering so provide the excellent manoeuvrability required. Combined with the special design of stainless steel propellers that can stand up to arduous operations, the combination has revolutionised operations in ice. This combination allows a more subtle approach by using manoeuvrability rather than brute force to create a channel.
SHIPBUILDING
28 April 2013 - 22:31
Propulsion in the ice
Operating in ice requires a very special type of vessel and in turn those vessels require a special type of propulsion, as described by Dag Pike.
SHIPBUILDING
28 April 2013 - 22:31
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