The prediction of calm opportunities for landing on a ship: Aspects of the problem

Motion sensitive operations at sea are conducted in an unpredictable environment; occasionally these operations can be planned around suitable weather forecasts or delayed until smoother motions are apparent. Furthermore landing operations require a perfect stability of the ship in roll, pitch and heave. Being able to predict these ship motions would make the landing safer and extend the operational limits, so during these periods it is easier to perform certain sensitive operations. The aim of this study is the characterization and prediction of calm opportunities (named Quiescent Periods QP), through a multi-resolution analysis by means of a wavelet decomposition. These QPs occur because of the random nature of sea states which is reflected in the nature of the ship motions. The ability to predict their occurrence is expected to be an effective help in the safety and success of a large number of sectors in the shipping industry (offshore sector, float over installations, remote operator vehicle handling, landing take off helicopters and UAV,...) where the viability of certain types of operations depend on wave induced motions and on the need for a short QPs, in which it is possible to conduct an operation safely. This study is a part of EDA Project “Quiescent Period Prediction (QPP)” that is dedicated to the study and development of a methodology for the prediction of the onset and duration of the Quiescent Periods of ship motions, particularly in bad weather, that limit the operational capability of the ship, for example that may hinder tasks such as launch and recovery of Rigid Hulled Inflatable Boats (RHIBs), RAS, floater motion to assist motion critical offshore operations and platforms, LNG-offloading connect, helicopter landing, automatic UAV landing, naval ships conducting flight operations etc.