Look, no sick bag!

By Duncan Graham-Rowe SEASICK passengers and crew could soon be feeling much better in rough seas thanks to a new way of damping the rolling of ships. The Japanese invention can cut the rolling of ships by up to half and can easily be fitted to both cruise ships and car ferries. The Hybrid Anti-Rolling System (HBARS) has already been tested in open water on the Mirai, an oceanographic research vessel built for the Japan Marine Science and Technology Center of Tokyo. From waves up to 4 metres high, which are considered rough, to typhoons where the waves are as high as 17 metres, it reduced the rolling and also improved the ship’s manoeuvrability. Some people are notoriously prone to seasickness even in quite light seas, including Admiral Horatio Nelson. “Anything that’s going to reduce the motion will make people feel better,” says Neil Walker, a naval architect with the consultants Global Maritime. He says that seasickness, and motion sickness in general, are related to how much the vessel or other vehicle moves and the frequency of the motion. Reducing the roll of a ship cuts both the extent and frequency of motion. HBARS, which was developed by the engineering company IHI in Tokyo, has a 100-tonne mass of metal mounted on rails. Sensors measure the motion of the ship and feed information about the roll to a central computer, which controls the movement of the counterbalance by means of electric motors. According to Saeki Aiichiro of the Strategic Planning Group at IHI, this approach has distinct advantages over existing systems, such as the fins in the water that help stabilise the motion of most passenger ships. “The system has good performance, even when drifting, while the fin-stabiliser is efficient only for cruising,” says Aiichiro. Besides providing a more pleasant journey, on the research ship the device makes it easier to lower delicate equipment into the water and to take it out. The motor has two roles, says Aiichiro. One is to decrease the speed of the mass while it is moving relatively quickly, such as in the middle of the roll, and the other is to speed up the mass when it is moving too slowly to damp the motion effectively. When the mass is being slowed down, its kinetic energy is transformed into electricity to save energy. According to IHI, this makes HBARS ideal for ships with limited power supplies, including passenger and car ferries. By using a weight that is less than 2 per cent of the ship’s displacement weight, a 50 per cent cut in roll can be achieved in choppy seas. Unfortunately, as the roughness of the sea increases the effectiveness of the device decreases,
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