Reference-Point Algorithms for Active Motion Compensation of Towed Bodies

Active heave compensation systems are typically single-degree-of-freedom systems that operate vertically to attenuate the vertical effects of wave motion. To apply compensation to towed bodies, which experience significant multiple-degree-of-freedom disturbances, a generalized motion compensation system using a “reference-point algorithm” is required that determines the length of a tow cable that should be reeled in or reeled out by an on-board winch system in response to external wave motion. This paper proposes, implements, and assesses four different reference-point algorithm approaches in both simulation and experimental environments. Of the proposed reference-point algorithms, the method that directly accounts for the tow cable angle proved to be most effective in both simulation and experimentation. It was found that there was little improvement between real-time measurements of the tow cable angle and a constant nominal tow cable angle-indicating a potential cost saving opportunity through the avoidance of real-time sheave-angle measurement.