As with all engines, a ship's engine needs to be cooled. However, with both boats and ships there is an advantage. They can use the water they are floating or moving in to cool the engine provided there is the correct equipment to prevent water from seeping into the ship. The only drawback on this is the potential for leaks in the air to water system, which can cause a boat or ship to fill with water and sink, and corrosion caused by the salts in the water and the debris clogging the cooling system by pollutants, zebra muscles and other mollusks. Cleaning heat exchanger tubes on large ships can be a very difficult job that requires the right expertise and the right equipment.