Davis and English 



Fig. 3 - Main particulars of the FHE 400 



split between two shafts in each strut, for the same purpose. Within the propul- 

 sion pods the drives are regrouped and reduced to the propeller shaft speed by 

 means of compound star gears. It will be appreciated that this gearing system 

 is very sophisticated, and yet it is only one of the many new developments that 

 have been necessary in the production of this ship. 



Early experience obtained with fully cavitating propellers of similar power- 

 ing on the hydrofoil ship Denison were disappointing (Ref. 3). Fatigue ^failures 

 occurred until thicker screws were used, and eventually titanium was employed 

 as a material to avoid this difficulty. With this foreknowledge, De Havilland de- 

 cided upon an extensive hydrodynamic and structural test programme, in an ef- 

 fort to develop efficient screws that would have adequate structural integrity. 



SCOPE OF HYDRODYNAMIC DESIGN AND TESTING 



Hydrofoil ships, like other types of high-speed craft, usually exhibit resist- 

 ance characteristics, with a maximum occurring at the transition from the dis- 

 placement mode to the flying mode. Once the speed at which the maximum re- 

 sistance occurs has been passed, the resistance decreases before beginning to 

 rise again at the high-flying speeds. Any propulsive device must, therefore, be 

 capable of producing the required thrust over a widely varying range of operat- 

 ing conditions. Fixed-pitch noncavitating propellers, such as those used on 

 trawlers, have a remarkable capacity for accommodating a large range of 



964 



