DESIGN DATA FOR HIGH SPEED DISPLACEMENT-TYPE HULLS AND A 
COMPARISON WITH HYDROFOIL CRAFT 
W. J. Marwood and A. Silverleaf 
National Physical Laboratory 
Teddington 
This paper is intended as a preliminary design guide and as a prelude 
to a more comprehensive research programme on high speed displace- 
ment-type hulls. 
_ It includes a short survey of available NPL data on the resistance, 
propulsion, and running performance of this type of hull and a brief 
discussion on the shallow water effect. 
The research programme planned at NPL is outlined and a descrip- 
tion given of the first of a series of torsionmeters designed at NPL 
specially for use on trials of small high speed craft. 
Finally some estimates are given of the power requirements of a 
suggested form of mixed craft in which the total weight is supported 
partly by the buoyancy of the hull and partly by fully submerged 
hydrofoils. 
INTRODUCTION 
Many small boats, such as patrol launches, work boats, and pleasure craft, operate at 
speed/length ratios of 1.2 to 3.5 (or Froude number F, about 0.4 to 1.2). These boats tradi- 
tionally have round-bilge displacement hulls, but there is very little published information 
about them to help their designers. While systematic series of model experiments have been 
made for most types of larger vessels, the relatively high cost of model tests has made it 
difficult to persuade owners and builders of small high speed boats to commission model 
experiments for new designs. Consequently there has long been a tendency to base hull 
designs for small boats on previous forms presumed to have been successful, without any 
proper basis for assessment of performance. 
This paper is intended as a preliminary design guide and as a prelude to a more com- 
prehensive research programme on this type of hull form which is being carried out at the 
Ship Hydrodynamics Laboratory of Ship Division, NPL; the large high-speed towing tank 
there will enable experiments to be made in better conditions than previously, including 
systematic measurements in head and following seas. The present paper is a short survey 
of available NPL data on the following aspects of the design of high speed displacement- 
type hulls: 
1. Resistance of Round-Bilge Forms 
(a) Average results for models 
(b) Effect of beam/draft ratio and LCB position 
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