Application of ship motion prediction II

The Automatic Control Group at UCL has been studying adaptive motion predictors, and their application to ship motion prediction. A recent project used an instrumentation and software package installed on a Type 22 Frigate for six weeks. The motion data has since been analysed to predict roll motion overshoots of, say, 5 deg at look ahead time horizons of the order of 10-15s. The results indicate that the motion predictor could be used to improve the safety of operations such as landing helicopters onboard ship. Many applications for this technology occur in marine operations, such as in the transfer of payloads between vessels at sea or between supply boats and offshore installations. Another is heave compensation, where a winch is controlled to keep subsea equipment such as ROVs or diving bells at constant depth despite motions of the mother ship. This paper describes the instrumentation system used for logging and predicting roll motion, based on the TSS 335 heave/pitch/roll sensor. The theory of adaptive prediction is briefly summarised. The software logs the motion data from the accelerometer system, runs the predictor and displays actual and predicted motions on line. The display is a Windows based graphics interface which can operate at several levels for operator, engineer and system designer access. The paper contains detailed results of using the prediction system on ship data and quantifies the level of operational improvement possible. This showed that roll prediction reduced the potential crashes - as judged by landing while roll exceeds some prescribed operating limit, for example 5 deg - from about 70% to under 30% and the number of correct predictions rose from 30% to about 80%.