Pneumatic anti-ice system

The pneumatic anti-ice system of a vessel is housed in the underwater part of the ship's hull, in order to reduce ice sticking to the hull and thereby improve the ship's mobility when sailing in ice. Modern pneumatic anti-ice systems use compressed air or engine exhaust as the working gas, which is vented overboard through a series of ejectors from bow to the amidships of the vessel. Since the ejectors are located at a depth below the waterline or in the area of the keel of the vessel, the airflow streaming from them forms an anti-icing water-air curtain along the entire underwater part of the hull.

History
The concept of a ship anti-icing system in the form of a water-air boundary layer was proposed for the first time in 1966 in the USSR, but its initial versions were imperfect due to the location of ejectors only in the bow of the ship and due to insufficient airflow. Variants of a heated steam-air system in the waterline area were also considered, and the prospects for its use as a thruster to increase the maneuverability of ships were also studied. The air washing system in its modern form was proposed by the Finnish company Wärtsilä in 1969 and was first installed on the Finnish cargo ferry Finncarrier, which was tested in the ice of the Baltic Sea in 1970. The first icebreaker on which the pneumatic anti-ice system was installed was the Yermak, built in 1974.

Performance
The adhesion of the underwater part of the hull with ice has a thermal and electrostatic nature. Since the ice in its above-water part also has a negative temperature at a negative temperature of the air, when interacting with the hull, the ongoing processes develop too quickly to warm it up to the ambient water temperature, as a result of which it freezes or sticks to the hull. Air flushing reduces the contact area of the ice with the hull and increases the temperature by creating an upstream current of warmer water from a greater depth, thereby solving the first problem. Another mechanism is the accumulation of an electrostatic charge in ice when it cracks and breaks. In the case of an unsatisfactory state of underwater paint coating of the hull, it can become ineffective against the sticking of ice with the accumulated charge.