Davis and Oates 



subject to large lift changes due to changing from fully wetted to fully or partially 

 cavitating flow. The bow foil system can be designed to provide a low 30^/^0. 

 and the optimum BCl/^H. 



Some of the interrelated problems to be examined and solved are listed 

 below: 



1. Hydrodynamics— (Foil section design, cavitation suppression, ventilation 

 effects, hydrodynamic loads, performance predictions, etc.) 



2. Hydrostatics 



3. Hydroelastics — (To date there is no accurate and proven method for 

 predicting flutter speeds of surface piercing or cavitating foils and much re- 

 search still needs to be done.) 



4. Dynamic Stability— (The stability equations had to be developed together 

 with a method for simulating the random seaway.) 



5. Structural Integrity— (Lightweight structures of adequate stiffness are 

 difficult to design and required sophisticated analysis.) 



6. Materials — (High strength materials had to be found for the foils and 

 random fatigue studies conducted. Coatings had to be developed to help guard 

 against corrosion and erosion.) 



7. Transmission Design— (As with many other hydrofoil problems this is 

 practically at the current limit of the "state of the art" in gear technology be- 

 cause of the high torque and low weight requirement.) 



THEORETICAL EQUATIONS OF MOTION 



Hydrofoil Ship Simulation 



Two methods of simulating the motions of a surface piercing hydrofoil in a 

 random seaway have been derived and both methods were used in the design of 

 the hydrofoil under consideration. 



The first method is based on the normal aircraft equations, in which sets of 

 partial derivatives representing the sum of various force or moment contribu- 

 tions are used to simulate the craft dynamics. The second method differs from 

 the first in that the various forces at the craft centre of gravity are obtained by 

 summing the forces developed by each foil element. Moments at the e.g. are 

 the product of these elemental forces and their respective moment arms about 

 the e.g. 



The first series of studies to broadly define the hydrofoil was carried out 

 in calm water using linear equations of the aircraft type suitably modified to 

 account for free surface effects. Small perturbations were assumed and a se- 

 ries of partial derivatives was calculated for the complete hydrofoil. These 



614 



