Sohmi-tke and Jones 



based on passively stable surface -piercing hydrofoil systems, there- 

 by complementing U. S. effort on automatically controlled fully- sub- 

 merged systems. The principal relative merits of each type are list- 

 ed below ' ' . Fully- submerged systems offer : 



a) a smoother ride in moderate to heavy seas, 



b) higher lift-drag ratio, 



c) lower foil system weight, 



d) greater foilborne manoeuvrability, 



e) retraction capability, 

 Surface -piercing systems offer : 



a) inherent stability, 



b) a wider range of foilborne speeds, 



c) better sea -keeping at hullborne speeds, 



d) higher potential for remaining foilborne in extreme seas, 



e) greater tolerance to off-design loads, such as those im- 

 posed by towed sonar. 



Successful contouring of large waves requires that the bow 

 foil respond rapidly to changes in immersion depth ; for satisfactory 

 following sea operation, the bow foil must also be reasonably insensi- 

 tive to wave orbital velocities. Together these requirements dictate 

 that the bow foil combine high rate of change of lift with draft, 4^- , 



with low rate of change of lift with angle, . 



da 



The after foil, on the other hand, must have high — — to pro- 

 vide adequate damping of seaway-induced motions. Furthermore,-^— 

 must be lower than at the bow foil in order that downward heave dis- 

 placements cause upward trim. Since foil efficiency generally in- 

 creases with ~= , a canard configuration is the logical result, with 

 the bow foil carrying as little weight as dynamically feasible. 



A secondary but significant advantage of the canard configura- 

 tion is that it lends itself to a hull with very fine bow lines. This is 

 necessary for reduced pounding due to wave impact when foilborne and 

 is particularly important for the Canadian role with its emphasis 



294 



