High-Speed Planing Hull for Rough Water 



At a smooth water planing speed of 45 knots, this craft is 

 expected to run at a trim angle of 3. 3° and develop ( V^r*) _ = 



0. 4 g in a State 3 head sea. 



It will be noted that a nominal 20° deadrise hull has been 

 selected. Considerations were also given to deadrise angles of 10° 

 and 30°. The details of these calculations (which follow the previous 

 procedures) will not be presented, but the results will be summariz- 

 ed. Figure 9 presents a plot of resistance-weight ratio (R/A ) 

 versus trim angle for deadrise angles of 10° , 20° , and 30° . These 

 results follow from Reference 1 . Superposed on Figure 9 are the 

 maximum trim angles for combinations of deadrise and beam which 

 will result in (vqq) a = 0.4 g when the 150, 000 lb. craft runs 

 at 45 knots in a State 3 head sea. 



Considering the 30° deadrise case, it is seen that a 14 ft. 

 beam requires a trim angle equal to or less than 5° to satisfy the 

 impact requirements. Further, the minimum drag-lift ratio for a 

 30° deadrise craft occurs at a trim angle of approximately 5°. This 

 high trim angle could impair visibility during high-speed operation 

 and was thus not considered acceptable. A reduction in trim angle to 

 improve visibility would reduce the impact loads below the maximum 

 acceptable value but, according to Figure 9, would significantly in- 

 crease the drag -lift ratio to values substantially larger than for the 

 20° deadrise surface. Thus, the 30° deadrise case was not further 

 considered. 



A 10° deadrise surface having a beam of 14 ft. would be 

 required to run at a trim angle of 2. 4° so as not to exceed the de- 

 sign impact acceleration. For this case, the drag -lift ratio would be 

 slightly less than that for the 20° deadrise surface. The boat length 

 and LCG position for j8 = 10° , t = 2. 4° , b = 14 ft. , A = 150,000 

 lbs. and V^ = 45 knots are computed from the monograph given in 

 Figure 19 of Reference 1 : 



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