nondimensionalized by dividing by the still water speed V^; namely, design and two-thirds 

 design speed for the respective ships. Consequently, these figures do not compare the re- 

 lative performances at identical values of the still water Froude number F^. Therefore, proper 

 interpretation of these figures requires that one consider not only that the ships represent 

 different degrees of fullness, but also that the still water speeds for the three ships differ. 

 In each of these figures it is seen that the critical region for speed loss in waves of constant 

 height occurs at approximately the same k/L value for the three models. For example, in 

 Figure 27 for h/L = 0.017 and V^ = V^, the design speed in still water, the maximum speed 

 loss occurs around X/L = 1.15. For the higher wave height h/L =0.033 and the lower thrust 

 Vq = 2/3 Vj, the critical region, while the same for the three models, shifts toward the shorter 

 wave lengths. These figures show also that the destroyer escort loses considerably less speed 

 than either the cargo or merchant ship, there being little difference between the latter two with 

 the exception of the case of h/L = 0.033 and thrust for two-thirds design speed. While the 

 variation in block coefficient is greater between the Series 60 and the SAN FRANCISCO than 

 between the destroyer escort and Series 60, it must be remembered that the design speeds of 

 the Series 60 and the SAN FRANCISCO are much lower (17 and 14 knots, respectively) than 

 that of the destroyer escort (25 knots). It is well-known that slow ships lose more speed 

 in a seaway than a fast ship, under identical conditions. 



In Figure 31 a comparison of the speed loss for the three models is made for waves of 

 h/L = 0.017 and V^ = 14 knots (ship scale). When compared at the same still water speed, the 

 Series 60 and SAN FRANCISCO showed the same maximum speed loss while the destroyer 

 escort's loss in speed was 7 percent less. It can also be seen in the figure that the critical 

 wave length to ship length ratio shifts toward the higher values for the models of fuller form. 



CONCLUSIONS 



This study shows that if a 1 percent error is acceptable, standardization trials can be 

 effectively conducted for the destroyer escort with thrust for design speed (25 knots) in waves 

 whose length is as large as 0.75 ship length if the wave height does not exceed 3 ft. At lower 

 thrusts the acceptable sea conditions are correspondingly reduced. The acceptable sea condi- 

 tions for standardization trials on slower and fuller ships of the Series 60 and SAN FRANCISCO 

 type are more limited. 



A comparison of the speed loss experienced by the three models with thrust for the same 

 still water speed shows equivalent speed loss for the merchant and cargo ships with the speed 

 loss for the destroyer escort being less by 7 percent. 



The critical wave length (wave length for maximum speed loss) for constant thrust was 

 found to shift toward the shorter wave lengths with increasing wave height. For any wave 

 height, the critical region shifted to the longer wave lengths as the tow force was increased. 

 This trend was observed for each of the models tested. 



