47.1 INTRODUCTION

We have all been fascinated, at some point in our lives, at least since the late 1950s, by the sight of boat-like vehicles that could skim over land or water with apparently little effort. Especially when, in 1959, such a craft crossed the English Channel in a couple of hours with three men on board.

The idea of reducing frictional resistance of vehicles by introducing a layer of air between the surface and the vehicle has been around since the beginning of the eighteenth century, if not earlier. For many good reasons, this concept was not put into practice successfully until the intervention of Sir John Cockerell, about 1952. His new ideas were implemented with great success, and a new industry was born.

It was widely believed that because of the air gap between the vehicle and the surface over which it hovered, that the friction opposing the craft motion would be no more than a little air resistance, as experienced by a car driven on a level, smooth road on a calm day.

It was somewhat of a shock, and a let-down, to discover that the over-water resistance was quite large and increased rapidly with speed up to a certain point, while over land; the ground had to be almost flat, with only little obstacles on it for the hovercraft to pass over or negotiate. As time passed by, flexible skirts changed all that, and the resistance over water was analyzed, quantified, and accepted...