High Performance Ships—Promises and Problems 5 
The ram wing will encounter all the problems of takeoff, landing, and in-flight control 
of ordinary aircraft, plus the precise control required in flying close to the surface. Take- 
off or low-speed power requirements may well prove to be governing. 
Stability and control behavior over waves is not well understood. Tests to date indicate 
problems associated with running trim even in calm water. Theoretical insight is being 
gained into the mechanisms of damping and resonant frequencies of motions over waves, but 
this is not complete, nor do we have as yet very much experimental experience. 
The scaling laws are being carefully examined, especially in light of the Sritish experi- 
ments with “hovercraft.” Here, for example, large scale tests indicated severe spray prob- 
lems, which did not arise in the small scale model tests. 
The dynamics of water-wall craft have not been examined extensively. How can we 
reduce air leakage through this water screen? We know that the screen is relatively good at 
short distances down from the jet exit, but leakage is severe at substantial heights before 
the jet hits the free surface. 
In all of these craft, a major problem is how to design the light structure required and 
still retain the ability to land and rest on the water in waves. Aircraft structure would be 
too light to meet the landing in waves requirement, while standard ship structure would be 
so heavy as to eliminate any payload. A blending is required. 
Light-weight, high capacity air fans are required that will operate against the high 
cushion pressure that is needed for ground-effect craft. It is estimated that for large, oper- 
ational ships this back pressure may be in the order of 150 pounds per square foot. Such 
fans are not shelf items. 
From the designer’s viewpoint, the promises are meaningful and the problems do not 
appear insurmountable. However, considerable expenditures of research effort and time are 
required, U.S. Navy work in this field, is aimed at the construction of a large ground-effect 
vehicle about 1963. The size and type await the results of research now underway. 
Submarines 
Just as the aircraft flies high and eliminates surface effects, the submarine departs 
from the free surface by submerging. Undesired motions are reduced rapidly with departure 
from the surface because wind-formed waves attenuate quickly with depth. Speed is also 
benefitted because it is no longer limited by the creation of surface waves. The submarine 
offers the ultimate in stealthiness. Thus, its principal promises are high speeds and a high 
degree of undetectability. 
Fig. 4 shows a comparison of the power to drive two hulls of about the same displace- 
ment where one is a modern submarine and the other a destroyer hull form. Part of the sub- 
marine’s advantage is its much superior propulsive efficiency. The remainder of the differ- 
ence is largely attributable to the elimination of wave resistance. These two effects more 
than balance the greater frictional resistance of the submarine which results from its greater 
area of wetted surface. 
