High Speed Displacement-Type Hulls 609 
J. B. Hadler and E. P. Clement (David Taylor Model Basin) 
The authors have suggested that a high speed displacement-type hull combined with 
partial hydrofoil support may show performance which is superior to that of a conventional 
boat. A number of years ago the Model Basin gave consideration to the same suggestion 
and established a program of investigation under our Bureau of Ships Fundamental Hydro- 
mechanics Research Program. A partial support hydrofoil system, composed of two sub- 
merged foils, each on a strut attached to the side of the hull were installed on a model of 
the U.S. Navy 52-foot aircraft rescue boat. These foils were arranged such that their fore 
and aft location could be varied as well as their angle of attack. The optimum location for 
these foils was 32.7 percent of the length forward of the center of gravity, and at a minus 
3-1/2 degree angle to the keel of the boat. At this condition the resistance was reduced 
throughout most of the higher speed range. For speeds below 15 knots, the resistance of 
the hybrid craft was somewhat greater. Between 15 knots and 30 knots the resistance 
decreased to about 75 percent of that of the conventional craft. Between 30 knots and 40 
knots, the average reduction in resistance was about 25 percent. Although these results 
indicated favorable performance for the hybrid craft, no further work was undertaken at the 
Model Basin because of the urgency of the hydrofoil program itself. Further research should 
be continued in this area, particularly in investigating the performance of the hybrid craft in 
seaways and with foils of the surface-piercing type. The full details of this work are con- 
tained in a Model Basin report entitled, “Tests of a Planing Boat Model with Partial Hydro- 
foil Support,” TMB Report 1254 dated August 1958. 
The resistance data for high speed displacement-type hulls which are made available 
in the paper are very welcome. A similar presentation was made by H. F. Nordstrom in his 
1951 publication, “Some Tests with Models of Small Vessels,” but in that paper the maxi- 
mum speeds are considerably below the maximum speeds for which data are given in the 
present paper. The data on the components of propulsive efficiency are particularly inter- 
esting and valuable, since little information of this kind has been previously made avail- 
able. It is noted that there is considerable scatter in the plots of these data, however, 
presumably because of significant difference in the hull forms and appendages of the boats 
represented. The usefulness of the data would be enhanced considerably if the authors 
would provide some additional information on those designs which were self-propelled. A 
profile drawing of the stern, including the appendages, would be particularly helpful. This 
would make it possible for designers to select values of wake and thrust deduction for the 
design most like the one with which they were concerned at the moment, and thereby obtain 
assistance in making accurate predictions of performance. 
W. J. Marwood and A. Silverleaf 
The authors first wish to thank all those who contributed to the discussion of this 
paper; their comments have greatly enhanced its value. 
Several contributors have discussed the relative merits of round-bilge and hard chine 
hull forms; however, the aim of the paper was solely to provide data on high speed 
displacement-type hulls, and there was no desire to make comparisons of a general nature 
between different basic forms. Commander du Cane’s views on this important practical 
point naturally deserve close attention, but it is necessary to use carefully defined terms 
when comparing hull forms. The round-bilge form as defined and described in the paper is 
without any chine or knuckle line which could affect the flow, and is in extreme contrast to 
the hard chine form used in some of the experiments in waves. Forms of these two types 
