Waves from Fast Ferries

Waves from fast ferries have become an environmental problem of growing concern to the public. Fast ferries produce not only higher waves than conventional ships, but also fundamentally different waves when they sail at supercritical speeds. Hitherto, ship waves have been considered as being generated by the ship hulls alone. Whereas this assumption may be reasonable for conventional ships with large hulls and limited propulsive power, the situation is different for fast ferries with their smaller hulls and very large installed power. Theoretical and experimental investigations seem to indicate that a substantial part of the wave making can be directly attributed to the propulsion system itself. Thus, two wave systems are created with different phases, but with similar frequency contents, which means that they merge into one system behind the ship, very similar to that of the hull alone, but with higher wave amplitudes. Conventional propellers will cause increased wave heights of about 10%, whereas water jets will cause increased wave heights of 20-40% as compared to those of the naked hull. This research is carried out in co-operation with the Danish Maritime Institute and the Danish Hydraulic Institute.