icebreaker(redirected from Ice-breaker)
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a separate structure or a device on bridge or dam piers to protect them from ice damage during ice drifts and to prevent the formation of ice jams. The principal element of an icebreaker is an inclined or vertical saddle-shaped edge that has a curved contour and faces upstream. The icebreaker receives the impact of the ice, breaks it into pieces, and directs it into the apertures of the bridge (or dam). Bridges that use piling have icebreakers built separately in front of the piers.
a vessel designed to sail through ice to maintain navigation in bodies of water that freeze over. The main purposes of icebreakers are to break up the ice sheet to open up a channel for other vessels and provide such vessels with the necessary assistance in moving through the ice; they are also used for independent voyages. A distinction is made between oceangoing icebreakers, including polar icebreakers (designed for the particularly heavy ice of the polar seas), and lake and river icebreakers. Oceangoing icebreakers, which escort ships over great distances, are sometimes called line icebreakers, and the largest of them are called leaders, in contrast to the smaller (auxiliary or port) icebreakers. Icebreakers are also divided into classes (groups) according to power.
Upon encountering an icefield, the bow of an icebreaker rides up over the edge of the ice and breaks it by the force of gravity. As it continues to move forward, the icebreaker overcomes the resistance of the broken ice in the channel it has formed, broadens the channel by breaking up, pushing aside, and crushing the ice with its sides, and then repeats the same cycle of movements. In practical terms the cyclical quality is weak, and the movement of the icebreaker may be regarded as continuous. In moving through broken ice, the icebreaker pushes small floes aside and breaks up larger floes. If the ice sheet cannot be broken by continuous forward motion of the icebreaker, the ice is then broken with blows (runs); for this purpose the icebreaker backs off and then picks up speed. Upon riding up onto the ice with its bow, an icebreaker may become stuck. The movement of even the largest icebreakers is frequently halted by ice jams. Among the measures used to free the icebreaker are fore and aft trimming or heeling (that is, longitudinal or transverse tilting of the icebreaker’s hull). For this purpose water is pumped in sequence between the trimming tanks (bow and stern) or heeling tanks (side), or ballast water is pumped simultaneously from the trimming tanks, making it possible for the icebreaker to sit higher in the water. Small river icebreakers are sometimes equipped with a vibration (rocker) device, which causes oscillatory movements of the hull in the ice and increases the effectiveness of icebreak-ing.
One or more ships may follow in the channel behind an icebreaker, depending on the severity of the ice conditions. In heavy ice, which impedes the movement of the vessel being escorted, the icebreaker takes it in tow, usually directly behind its stern. Two or more icebreakers are often used to escort a number of vessels simultaneously (a convoy).
The “ice qualities” of an icebreaker are determined by the ice performance and maneuverability. The criterion for comparative evaluation of the qualities of an icebreaker is usually its icewor-thiness—that is, the ability to make headway under certain ice conditions at a designated speed. The purpose of an icebreaker and the conditions of its operation also determine its design requirements.
The bow of an icebreaker has relatively sharp (wedge-shaped) formations, as well as a slant in the underwater portion at an angle of 20°-30° to the waterline, making it possible for the icebreaker to ride up onto the edge of the ice. The stern is designed for moving through ice in reverse and to protect the propellers and rudder from damage by ice. The incline of the sides also aids in the breaking and crushing of the ice during forward motion of the icebreaker, as well as in reducing the pressure of the ice on the hull structures in ice jams. The ratio of the length to the width of the hull (3.5–5.0) provides good maneuverability of the icebreaker in the ice, as well as straight-ness of the channel.
The hull of an icebreaker (particularly in its bow and stern extremities) is significantly stronger than those of vessels built for other purposes. The exterior cladding is thicker in the area of the variable waterline, forming the “ice belt.” Great demands are also made on the seaworthiness and safety of the vessel.
The power plant of an icebreaker is designed for frequent and rapid alternation of operating conditions; it should tolerate almost instantaneous stopping (jamming) of the propellers in ice and have high economy, to provide the greatest possible range without refueling. Therefore, power plants with an electric drive to the propellers have been widely used in modern icebreaker construction. Medium-speed diesels and steam turbines are used as the propulsion engines (gas turbines may also be used). The use of atomic energy has made possible the development of icebreakers with very powerful propulsion plants and virtually unlimited range. (The first atomic icebreaker, the Lenin, was put into service in 1959 in the USSR.)
Icebreakers are usually built with two or three heavy-duty propellers. In addition to the stern propellers, some icebreakers have one or two propellers in the bow, which increase their iceworthiness under certain conditions but make it impossible to use them in ramming.
Oceangoing vessels designed for independent navigation in the polar seas or for following icebreakers in particularly heavy ice are called icebreaking vessels (icebreaker transports or ships for other purposes).
The history of navigation in the northern seas goes back more than a thousand years. However, an active struggle against the ice was possible only after the contruction of metal vessels with mechanical propulsion mechanisms began. The first modern icebreaker was the small steamship Pilot, with a power of 44.2 kilowatts (kW), or 60 hp, which belonged to the Russian industrialist Britnev and in 1864 successfully traveled under icy conditions between Kronstadt and Oranienbaum. On this vessel for the first time a slant in the underwater portion of the bow was used, following the example of the White Sea ice boats, which made it possible for the vessel to ride up onto the ice with its bow and break the ice with its weight. Following the example of the Pilot, the construction of river icebreakers began in Germany (for the port of Hamburg) and then in other nations. These icebreakers were small vessels with a power of 110–960 kW (150–1,300 hp). The first arctic icebreaker, the Ermak, with a power of 6.6 MW (9,000 hp), was built in 1899.
Many Soviet icebreakers and icebreaking vessels, among them the Krasin, the Litke, the Sedov, and the Sibiriakov, played a major role in the exploration of the arctic.
The power of the main engines and the displacement of icebreakers varies within broad limits, depending on their purpose. In icebreakers built before 1973, the main engines have a power of up to 30 MW (44,000 hp), and the displacement is about 19,000 tons. Designs have been developed for considerably larger icebreakers, which are now under construction. Improvement in the efficiency of icebreakers is associated with the further improvement of their design and with the development of special devices for improving iceworthiness and maneuverability, for the provision of operability in ice jams, for protecting the propellers from damage, and for clearing ice fragments from the channel. The largest icebreaking fleets are in the USSR, the USA, Canada, Finland, Sweden, and Denmark.
REFERENCESVinogradov, I. V. Suda ledovogo plavaniia. Moscow, 1946.
Kashtelian, V. I., I. I. Pozniak, and A. Ia. Ryvlin. Soprotivlenie l’da dvizheniiu sudna. Leningrad, 1968.
Ledokoly. Leningrad, 1972.
A. M. ZAGIU
See also: ICE.