Savitsky 3 Roper 3 and Benen 



are easily warped to result in increased deadrise and curvature in the 

 bow sections. This combination reduces pounding and impact pres- 

 sures in a seaway. The transverse section shape above the lower 

 chine is increasingly more concave as the bow is approached. This 

 upper "flare" is desirable to deflect the bow spray outboard of the 

 deck and to provide additional buoyancy to reduce low- speed pitching 

 in a seaway. 



Spray Rails 



Spray rails are provided along both chines to assure flow 

 separation from the chines. The spray rail for the upper chine must 

 not extend into the separated flow cavity formed by the lower chine. 

 Otherwise flow reattachment will occur at high speeds. Separation 

 from the upper chine occurs at a speed-length ratio between 2. to 

 2. 5 while separation from the lower chine is expected to occur at a 

 speed-length ratio of approximately 3. 0. 



Final Design 



An artist's conception of the final design is given in Figures 

 12 and 13. 



MODEL TESTS 



Model tests were conducted at the Davidson Laboratory, 

 Stevens Institute of Technology to evaluate the performance of the 

 craft in smooth water and waves. A l/ll -scale model was used to 

 determine EHP and SHP. A l/l6-scale model was used to inves- 

 tigate the seakeeping, maneuvering, and turning ability of the craft. 

 Some of the principal results and test procedures are presented here' 

 in. 



Resistance and Propulsion 



Smooth Water Resistance 



A l/ll -scale model was constructed according to the lines 

 of Figure 10. To assure flow separation from the bottom, the upper 

 and lower chines of the model were sharpened by the addition of 

 mylar plastic strips which projected vertically a distance of l/32 of 

 an inch below each chine. Tests were made for a range of loadings 

 and speeds. The test procedure simulated towing the model through 

 the shaft axis. Measurements were made of the heave, trim, drag 

 and wetted areas. For the purpose of the present paper, Figure 14 

 presents a comparison between values of trim and drag computed by 



436 



