High-Speed Planing Hull for Rough Water 



directly from these design charts for arbitrary combinations of L/B, 

 l/C a » V, /\/L^ and H / 3 /B such as listed above. It is to be not- 

 ed that these results are for a trim angle of 4° and a deadrise angle 

 of 20°. Corrections for other combinations of trim and deadrise 

 angle will be described subsequently. 



For each assumed value of beam, the average CG accele- 

 rations for 45 knots in a state 3 head sea is obtained from the de- 

 sign charts of Figures 1-3 and plotted on the right half of Figure 4 

 as a function of length-beam ratio. These results are obtained by 

 extrapolations of the design charts as suggested in Reference 3 . The 

 ordinate of the plot in Figure 4 is the quantity : 



(Average) |_~4~ 3 Wj 



which defines the dependence of acceleration upon trim and deadrise 

 as developed in Reference 3. For r = 4° and =20°, the quan- 

 tity in the square brackets is unity so that y ^^ (Average) as given in 

 Figure 4, corresponds to the design charts of Reference 3 . Super- 

 posed on Figure 4 are curves of constant boat length for various 

 combinations of beam and length-beam ratio. 



The quantity r°/4 (5/3 - 0°/3O) is plotted on the left half 

 of Figure 4 for ease of applying these results to arbitrary combi- 

 nations of t and /3 . 



Some interesting observations can be made by an examina- 

 tion of the results in Figure 4 : 



Effect of Beam on Hydrodynamic Impact : 



All other conditions being equal, a reduction of hull beam 

 leads to significant reductions in impact load. For example, a 28% 

 reduction in beam (from 18 ft. to 13 ft.) results in a 69% reduc- 

 tion in impact accelerations (from 1. lOg to 0. 35g). Even a 1 ft. 

 reduction in beam, from 15 ft. to 14 ft. , decreases the impact ac- 

 celeration by approximately 2 9%. This powerful effect of beam 

 results from the large dependence of impact upon the inverse of beam 

 loading coefficient C ^ = A / W B . The effect of C A has long 

 been familiar to the designer of water-based aircraft (References 4 

 and 5 ) and has just recently been quantitatively identified by 

 Fridsma for the case of the planing hull. 



42 5 



