High-Speed Planing Hull for Rough Water 



the procedures of Reference 1 and the results of model tests. The 

 comparison is for a displacement of 150, 000 lbs. with an LCG of 

 38 ft. In the computational procedure, the upper chine beam (15. 7 ft. ) 

 is used for speeds up to 40 knots and the lower chine beam (14 ft. ) 

 is used for higher speeds. This was consistent with test results where 

 complete flow separation from the lower chine was observed at speeds 

 greater than approximately 40 knots (full-scale equivalent). An ef- 

 fective deadrise angle of 20° was used in the computations. 



It is seen that the computed and measured results agree well 

 enough to justify use of Reference 1 for engineering estimates of 

 planing boat performance. At speeds below 20 knots, extensive bow 

 immersion precluded application of the methods of Reference 1 

 which are restricted to prismatic -like planing hulls. Reference 6 

 will provide procedures for performance estimates at low speeds 

 where bow immersion is significant. 



It is interesting to note the complete absence of a "hump" 

 trim in Figure 14. This is attributed to the high-length beam ratio 

 hull which, for normal LCG positions, is constrained to run at low 

 trim angles. The low trim is, of course, most beneficial to improv- 

 ed seakeeping. 



Self-Propelled Tests 



Self-propelled tests of the l/ll -scale model were carried 

 out to determine propulsion characteristics, e.g. wake fraction, 

 thrust deduction coefficient, relative rotative efficiency and, sub- 

 sequently, predictions of delivered horsepower. 



The test program included resistance tests of the partly 

 appended model, open water tests of the stock propellers used in pro- 

 pulsion tests and self-propelled tests of the l/ll -scale model for 

 overload and underload conditions (so-called "British" method) at a 

 number of speeds and displacement conditions. The open -water tests 

 were carried out with the shaft horizontal and with a shaft inclination 

 of 12°. Self-propelled tests were made with all three propellers 

 driving and instrumented. 



The rudders were not fitted for these tests since they are 

 located approximately 4 propeller diameters aft of the propellers, 

 out-of-line with any of the propeller races and, consequently, could 

 have little influence on propeller -hull interaction. 



Three propeller dynamometers were installed in the model 



437 



