An experimental study of the effects of finite water depth and lateral confinement on ships wake and drag.

Clément Caplier, Germain Rousseaux, Damien Calluaud, Laurent David

Friday 3 july 2015

13:45 - 14:00h at Amazon (level 1)

Themes: (T) Water engineering, (ST) River and coastal engineering

Parallel session: 16E. Engineering - River

Wash waves produced by ships disintegrate river banks and coastal lines. This phenomenon of bank erosion is mainly due to the height of the waves. Various factors govern the forming of these waves and their amplitudes : the geometry of the water channel, the shape and the speed of the boat, the speed and the direction of the current, etc. These factors play an important role on the waves generation but also on the drag of the ship and so on its fuel consumption. Whether to study the impact of wash waves on the ship's environment or its drag, the analysis of the generated wake is essential. Hence a fine characterization of the wave field is necessary. The measurements of wakes generated by hulls in towing tanks are generally performed with intrusive techniques such as resistive or acoustic probes. However these punctual techniques remain limited for the identification of the whole wake and full field techniques measuring precisely the wave heights in various points are thus indispensable. This study proposes a comparison of wakes generated by two generic ships based on a Wigley hull with block coefficients Cb=0.67 and Cb=0.89 respectively representative of maritime and fluvial ships. The wakes generated in deep water and shallow water configurations have been measured for different Froude numbers with non-intrusive optical stereovision methods, giving access to a detailed and complete definition of the generated wave fields. The drag of the ship hulls has also been measured in deep and shallow water configurations with a hydrodynamic balance. The results permit to study the influence of both hull and water channel geometries on the ship's wake (shape and angle), on the amplitude of the generated waves (bow wave, transverse and divergent waves) and on the hydrodynamic response (lowering of the water level around the hull).