High Performance Ships—Promises and Problems 21 
These three methods of reducing frictional resistance may have application to midget 
submarines, and possibly to larger craft, but theoretical and experimental evidence to sub- 
stantiate claims and predictions is yet to be acquired. These methods appear to have more 
promise in a relatively low range of Reynolds numbers than at the high Reynolds numbers at 
which large ships and submarines operate. 
Another approach to the goal of high speed is to increase the efficiency of propulsion 
devices. No dramatic improvements in this area appear to be in the immediate offing. How- 
ever, a number of promising new types of propulsive devices are under study and some older 
ideas are being refined—to name a few: supercavitating or superventilated propellers, pump 
jets, Kort nozzles, cycloidal propellers, oscillating fins, and two-phase flow jets. Details 
of these and others, would require too much space for this paper to encompass. 
To Control or Minimize Motions 
From the control point of view, there are a few devices that hold promise for competing 
with the highly efficient, standard ship rudder. One of these, the cycloidal propeller, is 
well known. Another is the jet flap, currently under study for aircraft. Design data, includ- 
ing mass flow vs rudder effectiveness, are being obtained. Yet, another competitor for the 
rudder is the ring airfoil developed originally for aircraft. Preliminary results indicate 
excellent control characteristics. 
The problem of minimizing motions by using devices has been part of the research 
effort of the Navy and Merchant Marine for many years. For roll control, gyrostabilizers, 
active fins, and Frahm tanks are available. Reexamination of the last named, in recent 
years, has shown that by good design, passive tanks can be quite effective in reducing roll. 
Considerable effort has recently gone into pitch stabilizers. Fixed fins at the bow can 
significantly reduce pitch. Under study today are moving fins at bow and stern and flapped 
ducted propellers. 
CONCLUSIONS 
High performance ships are basic and very vital objectives of Naval Research and 
Development. Within the last few years, these objectives have been pursued by special 
attention to unusual hull forms. A number of these forms are nearing readiness to be incor- 
porated in useful craft; notable among these is the hydrofoil craft. 
Modern technical advances, especially in aerodynamics, hydrodynamics, and power 
plant development are exerting strong influences on ship design. For example, a hydrofoil 
craft was flown by Alexander Graham Bell at the end of the 19th century, but we would not 
be investigating, so thoroughly, the promises of hydrofoils if we did not today have high- 
power, lightweight machinery plants (marine gas turbines), an understanding of supercavitat- 
ing foils, and strong, lightweight structure. 
This is the time to look at our old compromises, and reevaluate them in the light of the 
new technology. We are not depending on “breakthroughs,” but rather recognize that the 
pace of advance has quickened and the breadth of the front has widened. 
The broad spectrum of craft shown in Fig. 21 illustrates the many types of marine 
craft, and their relative quasi-efficiencies compared to the well-known Gabrielli-Von Karman 
