Canadian Hydrofoil Program. Hydrodynamics and Simulation 



DISCUSSION 



U.S. 



Reuven Leopold 



Navy Naval Ship Engineering Center 

 Hyattsville, Maryland, U.S.A. 



Page 2 states that the bow foil, as the main control mecha- 

 nics, leads to high dL/dh for contouring of large waves ; however, 

 high lift versus depth slope for rough seas results in high vertical ac- 

 celeration. For the purpose of not losing momentary control in rough 

 seas and cause diving, the superventilating bow sections are used, 

 which in turn introduce additional drag. The question is this : while 

 reduction of drag and the improvement in ventilated flow stability are 

 definite objectives in all operating conditions, the requirements for 

 dL/dh are different at low frequency - that is calm seas - than at 

 high frequency - that is high sea states. The gain on c3L/c)h is fixed 

 for a constant speed and could not be modulated unless automatically 

 controlled surfaces were introduced. How does the author propose to 

 optimize c3L/dh for rough seas without compromising calm seas ope- 

 rations ? 



REPLY TO DISCUSSION 



Rodney T. Schmitke 



Defence Research Establishment Atlantic 

 Dartmouth, Nova Scotia, Canada 



The essential compromise is not between rough sea and calm 

 water operation, but rather between head seas and following seas. Op- 

 timization of c)L/c)h for head sea operation must of course be subject 

 to the constraint of providing adequate stability in following seas. This 

 constraint indeed limits the extent to which cSL/^h may be altered, but 

 we feel that at least a slight reduction is feasible and will result in 

 improved motions. We should point out that dL/^h at a given speed 

 may be adjusted, albeit not greatly, by changing bow foil incidence. 

 Thus in head seas the bow foil is trimmed down, lowering c)L/dh , 



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