There are several methods to investigate the blockage effect, among which the method of imaginary arrays for a model has advantages to take account of the influence of ship form parameters and the distribution of speed increase due to blockage around a model. On the contrary, the impropriety of this method applied to a model in a towing tank is to neglect the effect of wave motion on the free surface. However, it is supposed that the effect of the free surface may be very small for a practical range of low Froude number, and for usual dimensions of models and tank. In this paper, therefore, the calculations are based on the method of images for a body of revolution which is represented by a source ring distribution over the body, and some practical results are obtained concerning the blockage effect of a rectangular channel, speed correction for the current meter ahead of a model, the effect of finite depth of water and the effect of wake on the blockage corrector.
