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

The encounter of extreme waves, extreme wave groups or of unfavourable wave sequences is a dangerous thread for ships and floating/fixed marine structures. The impact of extreme waves causes enormous forces whereas the encounter of an unfavourable wave sequence — not necessarily extreme waves — can arouse critical motions or even resonance, often leading to loss of cargo, ship and 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 (see [1] and [2]) a new system for decision support on board 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 6 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 [3]. With the end of the joint project LaSSe — Loads on Ships in Seaway (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 on board a cruising ship can be provided, but also time windows for offshore operations are identified well in advance.