Off-loading-line motion compensation on vessels



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Here, several problems due to vessel motions during load handling on a floating vessel and their consequences are presented. In particular, off loading using a cable and winch is considered in detail. The cable is simplified as a spring with its mass attached to its end. The effect of this cable on payload motion is investigated and the need for controlling the payload motion for safe operation is clearly indicated. It is shown that a control system using feedback signals from the lower end of the cable can effectively eliminate undesired motions of the payload even during reasonably large vessel motions. A typical system is designed which will provide satisfactory performance and which requires only a nominal amount of winch power. The major, but solvable, problem is the transmission of the feedback signals from the end of the cable.