Canadian Hydrofoil Program. Hydrodynamics and Simulation 



established. Because these vertical acceleration spikes were an im- 

 portant source of motional discomfort, an objective of future develop- 

 ment must be to improve ventilation stability at extreme depths of 

 immersion. 



Foilborne sea time has not been sufficient to enable firm and 

 quantitative conclusions to be drawn regarding the suitability of bow 

 foil -^r— and -4^- for rough water operation. However, the ship never 

 experienced difficulty in following seas, while pitch response to head 

 and bow seas was high. It seems probable that a reduction in ~ "• of 

 about 20% would result in lower vertical accelerations without com- 

 promising stability. 



A high drag penalty is paid for using super-ventilated sec- 

 tions. The philosophy adopted during BRAS D'OR design was that 

 this condition could be tolerated since the bow foil is primarily a con- 

 trol element carrying only 10% of total ship weight. However, trials 

 and model test data indicate that approximately 3 0% of total foilborne 

 drag is due to the bow foil. In addition, the high bow foil drag makes 

 fuel consumption, and hence range and endurance, extremely sensi- 

 tive to longitudinal C. G. location. 



BRAS D'OR sea trials have therefore specified three objec- 

 tives for future super -ventilated bow foil development : reduction of 

 drag, optimization of Sj j= and ** L for rough sea operation, and im- 

 provment in ventilated flow stability. These are important conside- 

 rations, but are secondary to the demonstrated success of the super- 

 ventilated bow foil unit in stabilizing, controlling and steering the ship 

 over a wide range of speed and sea conditions. 



III. SIMULATION 



Hydrofoil simulation in Canada began with the extensive and 

 comprehensive studies carried out by the DeHavilland Aircraft of 

 Canada Ltd. in support of BRAS D'OR design ^ ^ . These studies 

 were subsequently supplemented at the Defence Research Establish- 

 ment Atlantic ' '->° ' , with the objective of achieving simple methods 

 applicable to all surface -piercing hydrofoil systems. It is largely 

 upon the latter work that this section of the paper is based. Four 

 topics are treated : the general equations of motion for surface-pierc- 

 ing hydrofoil vessels, prediction of steady state performance, analysis 

 of calm water stability and analog simulation of random seas. Because 

 of the close similarity to aircraft practice, descriptive material is 

 kept to a minimum. 



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