594 W. J. Marwood and A. Silverleaf 
Table 2 
Shallow Water Effect for a 51-Foot Launch in 20 Feet of Water 
Power in Shallow Water 
Speed/Depth Ratio Power in Deep Water 
1.285 
1.364 
1.330 
1.313 
1.270 
1.120 
1.035 
Probably 
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FUTURE WORK ON ROUND-BILGE FORMS 
While it is hoped that the preceding summary of data will be of use to the designer, it 
has also emphasized the scanty nature of the information presently available. Consequently, 
systematic investigations into high speed round-bilge forms are to be carried out as part of 
the research programme of the Ship Division, NPL. 
The round-bilge form Model 2084 has been taken as the parent form. Systematic changes 
in form will cover variations in displacement, beam/draft ratio, and position of LCB, and 
features such as the depth and width of transom and the slope of afterbuttocks will also be 
varied. The displacement range will cover that shown in Fig. 7, and speed/length ratios 
from 1.2 to 3.5, and to 4.0 in certain cases, will be investigated. 
Most of the model experiments will be made in the new large No. 3 tank at the Ship 
Hydrodynamics Laboratory of NPL. Its greater depth will allow higher speed/length ratios 
to be reached without encountering serious interference at the critical speed v/V gD , its 
greater size will enable larger models to be run so that reasonable size propellers can be 
fitted for propulsion experiments, and the wavemaker control system will facilitate experi- 
ments in irregular head and following sea conditions. The propulsion experiments will be 
made with at least three propellers of different pitch and diameter for each form so that data 
appropriate to different engine-propeller gear ratios will be obtained. Some detailed meas- 
urements of hull pressures are also planned. 
DISPLACEMENT HULLS WITH PARTIAL HYDROFOIL SUPPORT 
Recent studies of hydrofoil supported craft have included some interesting comparisons 
with high speed displacement-type hulls (e.g., Ref. 4). These naturally show that the effec- 
tive lift/drag ratio, or displacement/resistance ratio, is higher for displacement hulls at low 
speed/length ratios, and then significantly higher for hydrofoil craft at high speed/length 
