558 Edward V. Lewis and John P. Breslin 
stable system to variations ‘in the virtual (or effective) mass and virtual mass moment of 
inertia. It was found that the rate of decay of stable oscillations is not sensitive to virtual 
mass nor to virtual moment of inertia, which is in contrast to studies on deeply submerged 
bodies. Also for the case of 60 knots with 300 ft? of tail area, the sensitivity of the re- 
sponse to variations of M' and Z/ of +20 percent was determined and found to be quite 
small. Because several of the stability characteristics of this craft are so profoundly dif- 
ferent from those for which experience has been built up, it would seem worthwhile to con- 
duct model tests to check the predictions made here and at the same time to widen the scope 
of the study. This might be done through the use of an ultrasensitive motion-following ap- 
paratus or with the use of freely operating models. Certainly, the stability in the horizontal 
plane will be very important, particularly in view of the excitation in roll and yaw that will 
be provided by the long strut. These programs should be backed up by rotating-arm experi- 
ments to determine static and rotary derivatives near the surface and also by oscillator tests 
to determine the influence of heave and pitch frequencies. Seaworthiness investigations 
must also be made, particularly for the case of following seas, where critical operation may 
be encountered. 
CONCLUSIONS 
The possibilities of small, fast ships operating on or near the surface appear excellent. 
To permit the design and development of such craft, energetic research should be under- 
taken in the following hydrodynamic problems: 
1. Propulsion by means of high-rpm machinery, 
2. Drag of surface-piercing struts, 
3. Forces and moments on high-speed bodies near the surface, 
4. Depth control of near-surface bodies in following waves, 
5. Optimization of control surface arrangements on submerged bodies, 
6. Lateral control of a near-surface body with surface-piercing strut. 
Parallel research and development should be carried on in other areas that affect the de- 
sign of high-speed craft, particularly in the area of lightweight power plants. 
The Navy should be encouraged to design and build experimental limited-purpose ships, 
not intended to undertake normal operational duties in the fleet. These ships would be of 
inestimable value in guiding future research, development, and design. 
ACKNOWLEDGMENTS 
The authors wish to acknowledge the assistance of many members of the staff of David- 
son Laboratory, in particular Messrs. Edward Numata, Clayton Odenbrett, Paul Van Mater, 
and Robert Zubaly, for experimental work on different types of models; Dr. Pung Nien Hu and 
Mr. Paul Spens for theoretical and analog computer work; Mr. Charles Garland (now associ- 
ated with the J. J. Henry Company, Inc., Naval Architects, N.Y.) for design studies of semi- 
submarines, and Mr. Albert Strumpf for his advice concerning directional stability. 
