Uram and Numata 



on the Hydrofoil Semi- Submarine were such that the ship was free to surge, pitch 

 and heave; the variable ballast, hydrofoil flap and stem plane angles being set 

 for an equilibrium ship trim attitude at the design depth and run speed. During 

 the runs the model exhibited excellent stability and sought its own running 

 equilibrium trim condition for the speed of the run. Therefore, the ship depth 

 and trim attitude, in many cases was different from design conditions or from 

 those used in the tests conducted under restrained motion conditions. Figure 5 

 shows the pitch and heave equilibrium attitudes of the Hydrofoil Semi-Submarine 

 in calm water and we see that the assumed trim angle of the vessel varied 

 around the design equilibrium trim angle of zero degrees. We see, also, that 

 the submergence depth of the vessel varied around the design depth of approxi- 

 mately 1.5 diameters below the surface. Figure 6 shows the corresponding 

 calm water total resistance coefficient as a function of Froude number. Also 

 shown for comparison are results obtained from the restricted motion tests at 

 the design depth for various trim angles. The calm water resistance coeffi- 

 cient plot is, therefore, quite realistic; representing what might actually be en- 

 countered under operational conditions while the other curves give much lower 

 resistance coefficients under absolutely ideal conditions. The calm water re- 

 sistance coefficient was used in the calculations of horsepower requirements. 



Figure 7 depicts the mean equilibrium attitudes of the Hydrofoil Semi- 

 Submarine in regular waves. Not all of the data are presented here, but enough 

 are presented to give an idea of the range of conditions encountered. Figure 8 

 and Fig. 9 show the total resistance coefficient as a function of Froud number 

 for this ship under regular following waves. We see that there apparently is no 

 discernible difference in the drag coefficient with respect to the height of the 

 wave system in 1.0 L waves, whereas in wave lengths twice the ship length a sub- 

 stantial difference exists between the resistance coefficients for different wave 

 heights. Further, spotted onto these figures is the calm water resistance curve. 

 In both figures we see that the resistance coefficient in regular following waves 

 is higher than the calm water resistance, particularly for the wave height to ship 

 length ratio of 1/22.5. 



These resistance coefficients and resistance coefficients taken from Van- 

 Mater's [7] data for the Large Bulb Ship, Lewis' and Odenbrett's [6] for the 

 Semi-Submerged Ship and Davidson Laboratory data for a conventional destroyer 

 were used to calculate the horsepower requirements for the calm water and vari- 

 ous regular sea conditions. The standard calculation method for EHP was em- 

 ployed with the exception that a 30% increase in the Schoenherr skin friction co- 

 efficient was applied to the Hydrofoil Semi-Submarine to account for the skin 

 friction contribution of the main hydrofoil system and stern planes. This is 

 reasonable and in keeping with knowledge of the additional frictional resistance 

 experienced in normal submarines due to the sail, fair water, and stern planes. 

 Figure 10 gives an EHP comparison of the various unusual form ships and the 

 conventional destroyer in calm water. We see that up to 30 knots the power of 

 the Hydrofoil Semi -Submarine is substantially higher than the other three ships, 

 whose powers are comparable, because the Semi-Submarine experiences its 

 maximum wavemaking resistance in this speed range. Between 30 and 40 knots 

 all three unusual ship forms are better than the conventional destroyer. At 40 

 knots and above the Hydrofoil Semi-Submarine is substantially better than the 



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