Davis and Oates 



The predicted and measured response of the 1/4 scale manned RX craft 

 was used to verify the FHE-400 foil system design method. The motions of the 

 RX craft in a 1/4 scale random seaway were recorded on magnetic tape which 

 was then processed at the National Research Council Statistical Analysis Facil- 

 ity in Ottawa. Power spectral densities of vertical acceleration at the centre of 

 gravity, pitch angle, main foil lift and the seaway amplitude were obtained, the 

 last measured at a separate moored wave pole. 



The theoretical dynamic stability simulation results were recorded on mag- 

 netic tape and similarly processed at N.R.C. to obtain predicted power spectral 

 densities. The correlation between predictions and measurement is presented 

 in Figs. 19 to 25. 



Only head seas data is presented since following and beam sea motions are 

 of lesser magnitude and low frequency, making them less suitable for statistical 

 analysis and easier to compare visually. It has been found that sinusoidal anal- 

 ysis is adequate for the study of motions in beam and following seas. 



HYDROFOIL SfflP STABILITY CHARACTERISTICS 



This paper summarizes the methods developed for the design of the 200 ton 

 FHE-400 hydrofoil ship for the R.C.N. Since surface piercing hydrofoils are 

 usually required to be inherently stable, some comments on particular problems 

 are given. Longitudinal stability in pitch and heave is relatively easy to achieve, 

 provided that lift discontinuities due to ventilation or cavitation can be avoided 

 or minimised. Foil unit lift slope and heave stiffness can be optimized for head 

 and following sea response. Following sea "takeoff" is not a problem with the 

 canard arrangement discussed. Greater heave stiffness is required in following 

 seas and some compromise between pitch and heave motions and accelerations 

 is necessary. 



Open ocean operation requires a high ships' centre of gravity which com- 

 pounds the problem of achieving inherent lateral stability. The six degree of 

 freedom simulation revealed the need for roll stability augmentation of the 

 FHE-400 at low foilborne speeds. This is achieved by rotating the main foil 

 anhedral tips as "ailerons." At intermediate and high foilborne speeds, the an- 

 hedral tips are fixed since they provide adequate restoring forces without 

 change of incidence. The steerable bow foil gives positive directional control at 

 all operational speeds, both hullborne and foilborne. While the ship can be 

 steered "manually" at high speeds the simulation showed the need for a yaw 

 damper to prevent heading drift. 



The relationship between full size FHE-400 motions and the motions of the 

 1/4 scale RX craft are given in Table 3. 



Analog computer predictions of FHE-400 response in a random seaway are 

 given in Figs. 26 to 33. 



Figure 34 shows the plan and profile views of the FHE-400 prototype ship; 

 the bow foil and main foil units are illustrated in Figs. 35 and 36. 



646 



