Course Keeping of High Speed Craft in Stern Quartering Seas

There is considerable interest in the seakeeping performance of high speed craft. Researchers and designers have been working on advanced hull forms and ride control systems to enhance the operability of high speed passenger and patrol ships. An example of a recent development is the Enlarged Ship Concept (ESC) and the Axe Bow Concept (ABC), invented by Delft University of Technology. The ESC features a lengthening of the hull with high deadrise angle bow sections whereas the ABC goes a step further and has deep, vertical bow sections. These hull forms aim to reduce slamming while operating in head seas at high speed. DAMEN Shipyards, Royal Netherlands Navy, USCoast Guard and MARIN were involved in the ABC research project. After the research project was finished, DAMEN Shipyard applied it immediately – and successfully –. Several ships have been built by DAMEN and are successfully operated. These concepts have been studied extensively for head sea operation, for which the concepts are expected to demonstrate their capability to reduce the vertical accelerations. In addition to head sea operation, operation in stern quartering seas is important as well for these types of craft. When the wave encounter frequency is low and the waves are sufficiently steep, dynamic (in) stability phenomena such as broaching may endanger the vessel and its crew. A research program has been performed in which the performance of the ECS and ABC concepts in stern quartering seas has been compared by means of model tests. Also a novel bow rudder concept for improved yaw control has been investigated on the ABC ship. Results of a broaching analysis with a blended time domain strip theory and maneuvering method (FREDYN) will be discussed next. Next the capability of a time domain panel code (PANSHIP) to predict motions in stern quartering seas will be investigated and presented. The fundamentals of the method will be briefly outlined. Simulation results for ESC and ABC models with waterjet propulsion and steering, fixed skegs and a bow rudder (for ABC only) will be compared with the experimental results. The comparison will show to which extend the method is capable to predict effects of hull form and control actions on course keeping ability in waves.