2.5 Wave resistance component

The wave resistance R _W is caused by the waves the vessel generates following a straight course with constant speed U in calm water conditions. This means there are no incident waves. By waves we mean both the local wave elevation along the hull and the far-field waves. In Chapter 4, we discuss this in more detail and show that the wave resistance is influenced by the wetted hull form and the Froude number. Further, the air cushion of an SES generates waves which causes wave resistance. If the ship is in shallow water, R _W can be strongly influenced by the water depth h. A depth Froude number Fn _h = U/ ( hg) ^{0 . 5} is used to characterize this effect. Large changes in wave resistance occur around the critical Froude number Fn _h = 1 when h/L is small. There is no simple formula for wave resistance, like the one we have for viscous resistance.

An important part of wave resistance is associated with the energy in the far-field waves caused by the ship. The wave elevation can be measured along longitudinal cuts parallel to the ship s track, and the associated wave resistance can be calculated by assuming small wave slopes. This is called wave pattern resistance R _WP, but it does not account for the fact that the wave slopes can be large or that the waves break near the...