Each model was first tested in still water and the tow force was determined at several 

 speeds. Tests were then conducted for three still-water thrusts corresponding approximately 

 to 33, 67, and 100 percent design speed in head seas in regular waves whose length ranged 

 from approximately 0.5 to 1.5 ship lengths. The tests were made at wave heights of 1, 2, and 

 3 in. model scale corresponding approximately to values of ship length to wave height of 60, 

 30, and 20. Because of the severity of some of the above specified conditions the speed re- 

 duction was found to be so serious that the forward speed of the models could not be deter- 

 mined with any certainty. These regions of uncertainity are indicated in the graphs by the 

 dotted lines. 



The range of test conditions was somewhat limited by the capacity of the facility used. 

 To the extent that this range did not include possible sea conditions, the results are incom- 

 plete. 



DISCUSSION OF RESULTS 



In order to establish reference conditions for the wave tests, tow forces were found for 

 a series of speeds in still water. These forces were then corrected for the tare in the towing 

 system and the resistances so obtained are plotted in Figures 4a, 4b, and 4c. Wave tests were 

 performed for thrusts corresponding to approximately one-third, two-thirds, and design speed 

 for each of the ships. The experimentally obtained speeds for the various test conditions are 

 listed in the Appendix. 



Faired curves of speed versus wave height for constant wave lengths are plotted in 

 Figures 5, 6, and 7. The dashed portions of the curves indicate regions where the data have 

 either been extrapolated since the test conditions were beyond the limit of the test facility 

 used or the speed was somewhat uncertain because of the models' unsteady motion in the more 

 severe conditions. 



Figures 8, 9, and 10 obtained from Figures 6 through 7 show speed loss in waves for 

 constant wave heights. From these figures it can be seen that the region for maximum loss in 

 speed shifts toward the shorter wave lengths with increasing wave height for a constant tow 

 force. Furthermore, as the tow force is increased, the critical region shifts toward the longer 

 wave lengths for any wave height. This can be seen more clearly in Figures 11, 12, and 13 

 where the critical wave length has been plotted as a function of still water speed for various 

 wave heights. A comparison of these three figures shows that for the same still water Froude 

 number, the destroyer escort experiences maximum speed loss at lower values of \/L than the 

 other vessels. For example, considering the case of a tow force which could produce a speed 

 in still water corresponding to a Froude number of 0.2, the \/L for maximum speed reduction 

 for the destroyer escort was 0.9 while that for the Series 60 and SAN FRANCISCO was 1.0 and 

 1.13, respectively, when running in waves of h/L =0.017. The destroyer escort (Figure 11) 

 does not experience maximum speed reduction in waves of \/L of 1.0 and larger, and minimum 

 h/L of 0.017 until a still water Froude number of approximately 0.3 is obtained. 



