Hydrodynamics and aerodynamics start as one science and retain an extensive common base, including, for example, a wealth of fundamental theory and observation of streamline flows, boundary layers and vortical motions, (Plate 1).

But research and design have opened up the two frontiers in different directions, to support and often to lead the evolution and development of the respective fields of application — ships and aeroplanes, or ships and helicopters, or helicopters and other marine structures.

We are reminded of how far the helicopter has become an integral and indispensible part of the maritime scene and of so many maritime operations, and this is one of the best tributes to the great pioneering genius, drive and enthusiasm of Raoul Hafner who is very much in our minds as we consider the possibilities and prospects for cross fertilisation.

This paper describes the first work undertaken to see the flows of oil, kerosene, water or any other hydrogenous fluid within a steel casing. In the specific case described, the performance and movement of the oil in the scavenge system of the Rolls-Royce Gem helicopter gas turbine was clearly seen with the engine operating at a range of test conditions.

The work was conducted using cold neutrons from the DIDO nuclear reactor at AERE, Harwell, England, and this was the first time that such work has been attempted. The experiment was a complete success and provided answers to developmental problems in the oil system.

In the paper, the preliminary work on the ‘Herald’ reactor at AWRE, Aldermaston, leading to this breakthrough in technology is also described.

The paper reviews the development of amphibious hovercraft and considers the noise emission levels of current types of in-service craft. A brief reference is also made to side wall hovercraft and hover barges.

An outline of suggested methods for quantitative measurement of noise level and format is given, should legislation be deemed necessary at some future date.

Finally recommendations are made for further research and development programmes aimed at achieving significant improvement in the next generation of hovercraft.