Unconventional Propulsion — Silver leaf 



Underwater Bodies 



Marine propulsion devices are required for bodies other than ships. For 

 torpedoes and other underwater bodies, including weapons, quite different con- 

 siderations apply. Propulsive efficiency may not be at all significant and the 

 sheer ability to reach a high speed at whatever cost may be decisive. 



Future Possibilities 



The significant progress made during the past decade in developing fully 

 cavitating, contrarotating, and ducted propellers, and water jet propulsion sys- 

 tems, show that much can be achieved if the effort and the will are there. Con- 

 sequently, it would be wise to assume that the only limits to the further devel- 

 opment of unconventional propulsion devices are those imposed by basic physical 

 factors. However, for those of us who live in restricted economies in which the 

 principle of "either/or" must be recognized, it is essential to make the right 

 choice and not to dissipate research and development effort too widely. For 

 those who are apparently fortunate enough to live in "as well" economies such a 

 hard choice is, superficially at least, less necessary. However, it is a valuable 

 discipline in itself. Some of the factors which must inevitably determine the 

 emphasis in future research and development effort on marine propulsion de- 

 vices are: 



(a) The economic importance of the ships to which they might be 

 applied. 



(b) The engineering and operational difficulties associated with their 

 use. 



(c) The likely gains compared with those which can be achieved in 

 other ways, particularly by improving other parts of the propul- 

 sion system. 



(d) The relative importance of improvements in propulsion compared 

 with improvements which may be obtained in quite different ways, 

 such as by reducing crew costs and turn-around times or by in- 

 creasing the useful payload. 



It is a bold man who would venture a clear forecast in such circumstances. 



NOMENCLATURE 



A Area of jet nozzle, pump disk, or equivalent 



Cp = Pq y AV^ Power loading coefficient 



c^ = T 4 AV. ^ Thrust loading coefficient 



2 "'A 



914 



