Revisiting the influence of a ship’s draft on the drift force due to diffraction effect

ABSTRACT This study reviews alternative analytical methods accounting for the influence of ship’s finite draft on the drift force due to diffraction effect. In very short waves, the wave is completed reflected and no wave energy can be transmitted under the ship. As the wave becomes longer, however, only part of the wave will be reflected and the remainder transmitted. The reflected waves will induce drift force due to its interaction with the ship between free surface and draft. The former effect can be quantified by the reflection coefficient, while the latter can be account for by introducing the draft based exponential function ( ). When both effects are accounted for, a unified and theoretically more complete formulation results. The performance of the method is demonstrated by comparative results for a vertical plate of finite draft and a standard ship.