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Rotc
| Морской словарь |
Reserve officer training corps (u.s.).
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Rotor propulsion, английский
See flettner rotators.
Rotational oscillation, английский
Three of the six possible ship motions in response to the sea are pivoting movements. • roll is due to waves hitting the ship abeam, tipping it over on its side, pivoting around its longitudinal axis until the centre of gravity pulls it up again. an extra heavy roll is seldom due to inherent lack of stability, but probably indicates that the encounter period is close to the natural period of the vessel. (see also synchronous roll and parametric roll.) • pitch occurs when crests and troughs moving parallel to the ship toss its stem and stern upward and downward. this is effectively roll around the vessel’s transverse axis but, because a ship is far longer than it is wide, the effects are quite different. the period is longer and even a small angle is so magnified by the time it reaches the extremities that they may be lifted clear of the water. a raised bow can then slam back, producing a cascade of water across the forward weather deck and, possibly, a “whipping” effect throughout the length of the hull; while a rising stern can lift the propeller out of the water, with a danger of engine damage due to racing. experiments with anti-pitch fins have met with little success, and changing the vessel’s speed or course remains the most effective response. • yaw is oscillation horizontally around the vertical axis. in conditions of yaw, the vessel’s centre of buoyancy moves steadily forward in the desired direction while its stem and stern skid alternately to port and starboard. yaw caused by wave action in a seaway is especially difficult to control because wave profiles and pressures are not usually the same to port and starboard and these inequalities are compounded by orbital motion of water in the seaway as wave profiles change. moreover, at every half wavelength the water next to the rudder will be moving in the same direction as the vessel, compounding the helmsman’s problems. the winds and waves that cause these motions may come from anywhere and can rapidly change direction, but the ship’s period of encounter is more important than the absolute period of the wave-form or its direction. this is because the ship is moving relative to the seaway and will meet crests and troughs more frequently or less depending on its speed, and whether it is headed into the waves, diagonally across them, or broadside on.
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