THE Polarstern is a double-hull ice-breaker that can smash through sea ice 1.5 metres thick at a speed of about five knots, according to Bremen Business magazine. The vessel's master, Captain Lothar Suhrmeyer, who is also the captain with the longest period of service in Germany, said: ''The Polarstern is simply an excellent icebreaker.'' The vessel has a shell plating with a thickness of 57.6 millimetres in the bow region, while the sides are 43.6 millimetres thick. The forward area of the ship can withstand an ice pressure of 900 tonnes per square metre without any danger of deformation. About 3,400 expedition members, including about 800 foreign scientists have taken part in Polarstern trips over the last 10 years. The icebreaker is managed by Hapag Lloyd.