PRINCIPLES OF NAVAL ENGINEERING 



STABILIZING NOZZLES 



PERIPHERAL NOZZLE 



PROPULSION DUCTS 



CUSHION FAN DUCTS 



PILOT 

 HOUSE 



NOZZLE CONTROL VANES 



FLOTATION 

 COMPARTMENTS 



3.265 



Figure 25-4.— Air cushion system for SKMR-1). 



using the waterjet as a prime mover in small 

 craft such as the one shown in figure 25-5. 



The general principle of waterjet propulsion 

 is illustrated infigure 25-6. The "prime mover" 

 consists merely of a water pump. The rotating 

 impellers deliver thrust by accelerating a large 

 volume of water at a high velocity through a noz- 

 zle. 



The velocity of flow through the nozzle is di- 

 rectly proportional to the flow rate and inversely 

 proportional to the volume of flow times the ve- 

 locity of flow. 



One of the outstanding advantages of the 

 waterjet mode of propulsion is that the waterjet 

 produces much less underwater noise than a 

 conventional propeller-driven craft of the same 

 size and general configuration. Preliminary 

 studies of the waterjet indicate that a comparable 

 conventional propeller-driven craft could be de- 

 tected approximately ten times farther away than 

 the waterjet. 



Quite a different system of jet propulsion has 

 been suggested as a possibility for the propulsion 

 of underwater vehicles. This propulsion system 

 (fig. 25-7) is generally known as an underwater 

 ramjet system . The fuel in the combustion 



chamber reacts with the water; hence the water 

 that enters the combustion chamber may be re- 

 garded as a co-propellant. The products of the 

 reaction are expanded through a nozzle at the 

 after end of the craft, thus propelling the craft 

 forward. Although a propulsion system of this 

 sort would have many advantages for short- range 

 operation, there are some disadvantages; one 

 present disadvantage is that the system is ex- 

 tremely noisy. Also, it is very inefficient except 

 at very high speeds (above 80 knots). 



DIRECT ENERGY CONVERSION 



The production of power for ship propulsion 

 begins with the conversion of some stored form 

 of energy. In all present propulsion plants, the 

 stored energy that is the original source of power 

 must undergo a series of transformations before 

 it can be utilized to propel the ship. We have two 

 major sources of stored energy: fossil fuel and 

 nuclear fuel. In each case the stored energy must 

 be converted into thermal energy which is then 

 converted into mechanical energy.' 



During the past few years, a considerable 

 amount of interest has developed concerning 



634 



