Giddings and Wermter 



the basic nature of ship roll. It is felt that as nonlinear model tank simulations 

 are achieved and the model problem areas cited above are rationalized, the 

 model experiment will provide the most definitive design information. 



Model experiments should also be conducted to provide design information 

 for active fins and to evaluate the performance of existing designs. The Taylor 

 Model Basin is currently designing such an experiment to evaluate the fin per- 

 formance on a new class of destroyer escort. The same control device previ- 

 ously used during the activated stern fin experiments will be adapted to these 

 tests. Suitable control parameters of roll angle, roll velocity and/or roll accel- 

 eration will be selected. 



Additional experiments should be conducted on pitch stabilizing devices. In 

 at least two areas cited there is discrepancy as to the effect of aspect ratio. 

 These discrepancies might more fully be understood if the nature of varying 

 aspect ratio were more closely examined. Stefun [50] and Stefun and Schwartz 

 [51] vary aspect ratio independent of area. In both cases, the fin with larger 

 span (increased aspect ratio) perform more reasonably in reduction of both 

 pitch and vibration. Abkowitz [48] contends, however, that increased aspect 

 ratio will have the effect of increasing low pressure on the upper surface and 

 enhances the onset of breakdown. Laminar separation on the model may be the 

 cause of varying test results in this area. 



It would appear that for many naval applications, the use of pitch stabiliza- 

 tion devices would definitely be in order. In addition to the common arguments 

 in favor of stabilizing pitch for reasons such as stable radar sonar, or fire con- 

 trol platforms, Spens [55] makes one other valid point. He relates a pitch re- 

 duction to a possible decrease in freeboard and/or forefoot depth. When one 

 considers the design difficulty associated with increasing freeboard or draft of 

 smaller vessels such as destroyers any freeboard decrease would be a decided 

 design advantage. 



Increased depth and proper configuration design are the most important 

 parameters to consider in bow fin design. Since the maximum depth of fin is a 

 parameter not easily changed, lift control devices would have important design 

 application. Additional model tests should be conducted to find proper design 

 criteria and to clarify the hydrodynamics of the phenomena. In this respect, the 

 following areas should be investigated: 



1. Moveable flaps and jet flaps. 



2. Activated bow fins using the pressure on the suction face as a control 

 parameter. 



3. Additional boundary layer control studies. 



4. Additional investigation on parameters effecting relative bow motions 

 and the subsequent effect on performance of bow anti-pitching fins. 



5. Additional investigation of activated stern fins. In addition to conven- 

 tional devices already described, items such as ring control surfaces around 

 the propeller might be investigated applicably. 



6. Investigation of scale effect on model results such as Reynolds number, 

 near surface effects, etc. 



792 



