Unconventional Propulsion — Silver leaf 



40 



eo "J 



100 -! 

 < 

 o 



150 



04 0-6 0-6 



SPEED COEFFICIENT 



10 

 J = 



1-2 

 101- 5 Va 

 N D 



Va - KNOTS - INLET VELOCITY TO PROPELLER 



N - REV/VIN - PROPELLER RATE OF ROTATION 

 D - FEET - PROPELLER DIAMETER 



Fig. 9 - Useful range for fully 

 cavitating propellers 



wetted propellers, and this, coupled with the possible elimination of 

 some transmission gearing, may open the way to the wider use of FC 

 propellers for ships of lower speed than those for which they have been 

 used until now, although there are still numerous practical difficulties 

 to overcome before this becomes accepted practice. 



(c) Contrarotating propellers — These offer a way of increasing the power 

 which can be handled in cases of restricted diameter while retaining 

 the basic single "line of shaft" configuration, and under some condi- 

 tions these propellers can show considerable benefits. Full-scale ap- 

 plication is at present limited by the mechanical engineering problems 

 involved in producing a completely reliable transmission system, and 

 by the very considerable increase in initial cost compared with the 

 conventional single propeller. 



(d) Tandem propellers — The use of two screws fixed to a single shaft is 

 strangely reminiscent of very early attempts to make effective use of 

 the output characteristics of steam turbines. Tandem propellers do not 

 seem to have any marked disadvantages and they may well find unex- 

 pected applications. 



908 



