Overview

The work documented in this report is a programme of research started in 1977 following issue of CAA Paper 75017, ‘Report of the ARB Special Committee on Hovercraft Stability and Control’, sponsored by the Ship and Maritime Technology Requirements Board.

The aim of this work was to analyse the behaviour of hovercraft skirts in situations where the skirts may be dragged out of inflated shape as a craft moves forwards (plough-in), or partially or fully sideways (tuck under), causing roll and potential capsize.

Beyond the boundary where skirt tuck-under occurs the CAA intended the BHSR’s Chapter B5-1 to provide the requirements for righting moments to be provided by the craft hard structure. Note that key update HRC 43 issued 2^nd December 1981, provides the relevant guidance through revisions to Chapter B5-1.
An extract from the BHRS updates can be found here for reference.

Model testing was carried out and this as well as analytical work was used to construct procedures to determine stability limits for bag/finger and loop/segment skirts.

It may be noted that plough-in is a phenomenon usually associated with speeds above hump speed, while capsize may also be associated with speeds below hump in a seaway as the side skirts will be subject to much higher wetting loads.

The work of this report is focussed on the slow speed beam-on motion at the critical primary hump speed.

Using the tables and graphs in the report, it is possible to evaluate the restoring moment coefficient for amphibious hovercraft  with either bag/finger or loop/segment skirts, with or without anti-bounce webs, cushion internal keels, and tapered loop/bag geometry, or simple fixed segments.

The report can be accessed here.