| 摘要 |
<p>A drilling rig is kept in position at sea by variable-pitch propellors, which are used to counteract the effect of wind and current. They, are their electric motors, must be adequate for the severest weather conditions. Such conditions are rare, and the motors are much larger than is needed to cope with the (near-)clam weather that more commonly prevails. Thus a second electric motor is used whenever a low power output is adequate. The motor is (a) one propellor driven by the low-power motor or (b) one or two propellors each driven by a high-power motor.</p> |
