middle of the overall chord. Such flow relief was considered desirable in view of previous 

 experience with antipitching fins at the Model Basin. Tip fences, similar to those of Fin 

 No. 1, were also fitted. The plan area of the configuration outboard of the hull was again 

 2.2 percent of the load-waterplane area. 



Fins No. 2s and No. 2A were obtained by modifying the plan of Fin No. 2. Fin No. 2s 

 was obtained first by reducing the full-scale span by 10 feet so as to make the tip to tip 

 distance 28 feet, and the plan area was reduced to 1.4 percent of the load-waterplane area. 

 Fin No. 2h was obtained next by drilling holes corresponding to a full-scale diameter of 

 18 inches, 2 feet from the leading and trailing edges of Fin No. 2s, port and starboard. The 

 purpose of testing these modifications was to investigate the effects of a further reduction of 

 plan area, 1 and the possibility of decreasing the adverse effects of fin vorticity experienced 

 when the fins approach the surface. Such vorticity effects are considered structurally unde- 

 sirable. Tip fences were retained in both of the above modifications. 



Fin No. 3 Dihedral Configuration. This configuration retained the plan geometry of 

 Fin No. 1, and was obtained by rotation about the root chord. The dihedral angle was 

 30 degrees. The purpose of this configuration was to investigate the effect on slamming of 

 the wedge entrance so formed. It was for this purpose that the dihedral angle used was as 

 large as 30 degrees. This configuration was not fitted with tip fences. 



Fin No. 4 Triple Configuration. This configuration was rectangular in plan, and con- 

 sisted of three fins in series each corresponding to 28 feet by 12 feet. The plan area out- 

 board of the 3-foot waterline was 2.3 percent of the load-waterplane area. In this case, how- 

 ever, the upper surface of the fins was attached to the underside of the keel forward, with 

 more support provided by two thin struts, port and starboard. The middle fin had a clearance 

 corresponding to 1 foot from either of the forward or after fins. The purpose of testing this 

 configuration was to investigate the effects of deeper fin submergence on fin vorticity. Tip 

 fences were installed in this configuration. 



A modification, Fin No. 4A, was obtained by drilling holes of a full-scale diameter of 

 1 foot on both sides of each" of the three fins. 



INSTRUMENTATION 



Direct data obtained from the model tests included wave elevation, strain, and pitch 

 and heave amplitudes. All data taken were recorded on an 8-channel oscillograph recorder. 



References are listed on page 29. 



