Panel Discussion 



artificial ventilation in the way of the longitudinal steps would modify the flow. 

 It was pointed out that, in seaplane model tests, the afterbody area just aft of 

 the transverse step is open to the atmosphere to assure proper ventilation and 

 flow separation — particularly if there is a shallow depth of step in the design. 



3. RECENT TEST RESULTS FOR PLANING HULLS 



Professor A. Nutku of I.T.U. described model tests in the Turkish tank with 

 systematically varying hull forms to study the effect of geometric form, dynamic 

 planing conditions, and loading on the performance and resistance of planing 

 hulls. Geometric variations included flat bottom and constant deadrise pris- 

 matic hulls; varying deadrise surfaces; models with longitudinal variation in 

 beam, and slope of buttock lines. In addition, hard-chine and round-bottom sec- 

 tions were tested. Professor Nutku has planned an extensive systematic model 

 study of planing — however, his presentation at the panel discussion was limited 

 to a presentation of only some of the test results collected to date. Many interest- 

 ing performance characteristics were evident from the 13 data plots which were 

 presented. Unfortunately, limited space does not permit the reproduction of those 

 test results in this summary, and a discussion and interpretation of these data 

 cannot be adequately accomplished without these plots. The attendees at the sym- 

 posium expressed great interest in Professor Nutku' s experiments and eagerly 

 await publication of his work. 



A. C. Conolly of the Marine Technology Center of General Dynamics dis- 

 cussed a procedure to predict the performance of stepped planing boats from 

 model tests on a standard series of flying-boat hulls. The systematic seaplane 

 model data were obtained by the Davidson Laboratory, Stevens Institute of Tech- 

 nology and by General Dynamics. Conolly refers to the work of Saunders-Roe 

 in England in collapsing this data and making it easily usable by the designer for 

 pre-design purposes. The work of F. W. S. Locke, Jr., is also referred to in 

 this regard. Using these collapsed seaplane data, Conolly predicts the perform- 

 ance of a stepped planing boat with a plum stabilizer which had been model- 

 tested. He finds that the resistance was overestimated throughout the speed 

 range by about 15%, but the resultant resistance curve was of the same form as 

 the model and the predicted hump resistance occurred at the same model speed. 

 Seaplane data indicated a hump trim of 5.0°, whereas 5.8° was measured on the 

 model. At planing speeds both seaplane data and model data agreed. 



Dr. J. J. van den Bosch of Delft presented the results of a brief study on 

 the linearity of motions of planing craft in head seas. Two models were tested. 

 One was the series-62 type developed by Clement and Blount. The other was 

 derived from this model by increasing the deadrise angle. For test speed co- 

 efficients up to F\7 = 3.5, it is shown that, considering the pitch and heave mo- 

 tions, the derivation from linearity were small at wave lengths approximately 

 equal to the hull length, but that the derivations increased for longer wavelengths, 

 especially for Fy > 2.5. The accelerations were distinctly nonlinear for all wave 

 and speed conditions. Heave and pitch response amplitude operators obtained 

 from irregular and regular waves were compared at a Fy = 2.7. The agreement 

 was satisfactory for the high-frequency (short-wave) part of the spectrum but 

 poor for the low-frequency (long-wave) part. Dr. van den Bosch speculates that 

 the low-frequency part is not trustworthy because of the reflection of the very 



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