Sea swell compensation

摘要

A hoist includes a winch and a hoist rope having load attaching means on one end and a hydraulically-operated ram to heave in and pay out the hoist rope. Two hydraulic systems each including a gas accumulator are connected to the hydraulically-operated ram with selection means acting to selectively connect the hydraulic systems with the hydraulically-operated ram. The hydraulically-operated ram is biased so as to tend to heave the hoist rope by the gas pressure in the accumulators which are at different predetermined pressures so that the hydraulically-operated ram acts to support the weight of a load under the control of one accumulator to maintain tension in the hoist rope when the load is not fully supported by the hoist rope to compensate for relative motion between the load and the hoist; the other accumulator causes the hydraulically-operated ram to heave in the hoist rope when the hoist rope is tensioned and the load is entirely supported by the hoist rope. In an alternative construction the ram is replaced by a pump-motor.