Fin Number 4 







L $. I k. ' 



\ 14' I t 



+■ + 1 



^ h>- 12' — — f h" 1 2'tH h*- I2'-|H 



Fins separated by 1 ft. 



Upper surface of fin tangent to baseline. 



Fin Area: 640 sq ft. 



Fin Area 



= 0.023 



Waterplane Area 



Fin Number 4h 



Obtained from Fin Number 4, by drilling five 1-ft 

 diameter holes on each fin as indicated in sketch. 



Figure 4 — Views of Antipitching Fin 4 



FINS 



The program consisted in testing several antipitching fins to compare their relative 

 performance. The difference among the various configurations tested was one of plan 

 geometry. In profile section all fins were essentially flat plates with faired leading and trail- 

 ing edges. The intersections of the fins with the hull were fillet-faired. The principal char- 

 acteristics of the fins are shown in Figures 3 and 4. Figures 5 and 6 show photographs of 

 the various fins as installed on the model. Following is a description of the four types tested. 



Fin No. 1 Swept Forward. This fin had a leading edge normal to the direction of 

 advance, and a swept forward trailing edge. The purpose of the sweep was to reduce the load 

 near the tips and, therefore, the bending moment at the root. The thickness of the fin was 

 5/8 inch, corresponding to the apparently unrealistic full-scale thickness of 15 inches. The 

 leading edge of the fin was at a distance aft of the forward perpendicular corresponding to 

 2.38 feet full scale. The chord plane of symmetry was at the ship's 3-foot waterline. The 

 span of the fin, tip to tip, corresponded to nearly 41 feet. The plan area outboard of the hull 

 was 2.2 percent of the load waterplane area. Fences were installed at both tips of the fin. 

 These extended 18 inches full scale above and below the upper and lower surface of the fin. 



Fin No. 2 Twin Configuration. This configuration was rectangular, the span measure- 

 ment corresponding to 38 feet full scale. The chord plane of symmetry was as in the previous 

 case. The two fins making up the configuration were identical, had a chord corresponding to 

 11 feet full scale and were separated by a distance corresponding to 9.6 feet. The purpose 

 of the separation was to facilitate the flow around the fin by offering a passage through the 



