High Speed Displacement-Type Hulls 599 
leads are taken to a terminal block fixed to the shaft which is, in turn, connected to the 
inner unit of the slip ring assembly. 
This slip ring assembly has two main units: an inner unit fixed to the shaft which 
carries the slip rings themselves, and which rotates with the shaft, and a fixed outer ring 
which carries the pickup brushes. Both units are made in two halves, so that they may each 
be placed around the shaft and bolted together. The inner unit of the slip ring assembly is 
large enough to fit around a 6-inch-diameter shaft; it is fitted to shafts of smaller diameter 
by inserting a distance piece in one half, and clamping the other half in place by adjusta- 
ble, screwed feet. The outer unit carrying the pickup brushes is kept in position by rubber- 
tired rollers both radially and axially. 
The five slip rings are of silver-plated brass, accurately scarphed at the joints of the 
two half units. Four rings are used for gauge leads, and the fifth for counting revolutions of 
the shaft. The brushes are of silver graphite. The gauge outputs are measured either on a 
Baldwin and Southwark SR 4 or a Siemens strain indicator. The complete meter is calibrated 
statically by applying known torques to the shaft close to the propeller when the vessel is 
out of the water. 
The system has proved very reliable. The slip rings have behaved well, the strain 
readings are steady, and there is no appreciable zero drift. 
DISCUSSION 
Peter du Cane (Vosper Limited, Portsmouth) 
We at Vosper have been interested in this paper as it discusses the range of high 
speed craft in which we have specialised over the last 25 years. 
Within reason we agree that for V/\/Z, = 3.4 a round-form hull as suggested by the 
authors would be our selection though only because if 3.4 is assumed as a maximum the 
probability is that for continuous cruising V/V, = 2.5 might be expected. At V//I = 3.4 
we could certainly produce a hard chine planing form with better resistance qualities than 
the round form and in our opinion with at least comparable seakeeping qualities. 
It may be conceded that the subject of the relative merit of hard chine versus round 
form in waves is very relevant to this Symposium so that it is proposed to discuss it at 
some length: 
Reference 4, which is a paper I submitted to the R..I.N.A. in 1956 and which was 
mainly concerned in recording extreme values, is quoted in justification of the following 
judgement on the qualities of the hard chine planing form: “waves no more than 3 feet in 
height can cause slamming decelerations up to 9 g, injurious to both structure and person- 
nel, as recorded at sea.” 
It is felt there must be some misunderstanding of the data recorded in Ref. 4. Cer- 
tainly there was no question of 9 g being recorded in 3-foot waves. If this is inferred 
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