Critical Situations of Vessel Operations in Short Crested Seas—Forecast and Decision Support System

Abstract

The encounter of extreme waves, extreme wave groups, or unfavorable wave sequences poses dangerous threats for ships and floating/stationary marine structures. The impact of extreme waves causes enormous forces, whereas an unfavorable wave sequence—not necessarily extreme waves—can arouse critical motions or even resonance, often leading to loss of cargo, ship, or crew. Thus, besides a well thought-out maritime design, a system detecting critical incoming wave sequences in advance can help avoiding those dangerous situations, increasing the safety of sea transport or offshore operations. During the last two years a new system for decision support onboard a ship or floating/fixed marine structure named CASH—Computer Aided Ship Handling—has been introduced. The preceding papers showed the step wise development of the main components of the program code—3d-wave forecast and 3d-ship motion forecast. These procedures provide a deterministic approach to predict the short crested seas state within radar range of the ship, as well as resulting ship motions in six degrees of freedom. Both methods have been enhanced with special focus on the speed of calculation to ensure a just-in-time forecast. A newly developed component is the adaptive 3d-pressure distribution. This method calculates the pressure distribution along the wetted surface of the ship hull using a newly developed stretching approach. With the end of the joint project Loads on Ships in Seaway (LaSSe), (funded by the German Government) the paper presents the CASH system, giving the possibility to detect critical situations in advance. Thus not only decision support onboard a cruising ship can be provided, but also time windows for offshore operations are identified well in advance.