Introduction

Figure 5.1 shows an example of a surface effect ship (SES). Figure 1.8 gives a fish-eye view. The vessel is supported by an air cushion that is bounded by flexible seal systems at the bow and stern and by two side hulls. The aft seal is usually a flexible bag consisting of a loop of flexible material open against the side hulls, with one or two internal webs restraining the aft face of the loop into a two- or three-loop configuration. In equilibrium position, there is a very small gap between the bottom of the bag and the water surface. An example is a gap height of 3 cm. The bow seal (skirt) is usually a finger seal consisting of a row of vertical loops of flexible material. Details are shown in Figures 5.2 and 5.3. The seal material is rubber.

There is an air fan system (Figure 5.4) that provides the excess pressure in the air cushion and lifts the SES up, thereby reducing the water resistance. The excess pressure in the air cushion causes a water level inside the cushion lower than the level outside. Typically, the air cushion carries 80% of the weight of the vessel. The buoyancy of the side hulls carries the rest of the weight at zero speed. When the vessel speed increases, the vertical side hull forces due to the water are caused by both hydrostatic (buoyancy) and hydrodynamic pressures.