PROSPECTS FOR UNCONVENTIONAL MARINE 

 PROPULSION DEVICES 



A. Silverleaf 



National Physical Laboratory " • ' >■ < - '■' 



Teddington, England ^ ' • ■; • ' 



ABSTRACT ' ' • • ^ 



This paper is intended as a general review of some of the factors which 

 influence the development of propulsion devices for ships and other 

 marine craft. 



First, some general points are examined, and an attempt made to de- 

 fine criteria which help the designer to choose the propulsion system. 

 Although there are few rules which apply to all classes or types of ship, 

 the simplest useful parameter is the speed-displacement ratio; as this 

 increases, so does the specific power (or power per ton-knot), and thus 

 the power-weight characteristic of the propelling machinery becomes 

 more important. Generally, at low and at high values of the speed- 

 displacement ratio, the choice of main machinery and propulsion device 

 is fairly clear; difficulties occur at intermediate values. However, 

 high absolute power requirements also make choice more difficult. 



Next, the principal features of the main types of propulsion device are 

 outlined, and their potentialities and limitations considered. The long- 

 established, orthodox open marine propeller is still a most efficient 

 device for converting rotational energy into propulsive thrust, but its 

 range of application is not unlimited. To extend the range of efficient 

 operation, other types of screw propeller have been developed; these 

 include ducted, controllable pitch, contrarotating , and fully cavitating 

 propellers. Paddle wheels and vertical axis propellers, waterjets, and 

 airscrews have also been used for marine purposes, while air-blown 

 ramjets and magnetohydrodynamic devices have also been proposed. 



Finally, some of the hydrodynamic, engineering, and operational fac- 

 tors affecting particular ship types are considered in more detail. 

 Tankers and bulk carriers, high-speed container ships and other cargo 

 liners, passenger liners and ferries, and very-high-speed foilcraft and 

 hovercraft -all these have different needs and raise distinctive prob- 

 lems. Throughout it is stressed that the choice and design of a propul- 

 sion system for a ship must not be considered as a series of separate 

 units, but as an integral whole in which the characteristics of main 

 machinery, propulsion device, shafting or other connections, and needs 

 for auxiliary power must be closely related. 



INTRODUCTION 



This paper is intended as a general review of some of the factors which in- 

 fluence the development of propulsion devices for ships and other marine craft. 

 During the past twenty years there have been many remarkable changes in the 



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