2-2 8 BOAT HULL DESIGN 



Summary of Scantlings 



Shell Laminate: 1 ply cloth on outboard face, 1 ply mat and 1 ply woven roving. 



Transom: 1-3/8 in. thick, as required by OBC Standards (14). Sandwich construction - 

 1-1/4 in. thick waterproof Douglas fir plywood core, 1 ply cloth and 1 ply mat on aft face; 



1 ply mat and 1 ply woven roving on forward face. Mat plies placed next to plywood for 

 maximum bond and to reduce porosity. 



Gunwale, Thwart and Fore Deck: Molded in a single unit of 1 ply cloth and 2 plies mat. 

 Gunwale to be a channel section with 2 in. flanges and web; similar to Fig. 3-17. Thwart 

 to be a channel section with a 12 in. web and 3-1/2 in. flanges with an additional ply of mat 

 on the flanges, Fig. 2-2 0. 



Design 



Gunwale: Design Loading - Assume weight of boat as a concentrated load at the center 

 of the longest span. 



Factor of Safety =2.0 



Weight of Boat; estimated = 150 lbs. 



Maximum Span = 6.5 ft. 



Bending Moment, M = £=- (2.7) 



h 



M = lg£- x 6 ^ * 12 = 2925 in. -lbs. 

 It 



Use a premolded U-shaped gunwale, similar to Fig. 3-17, with a 2 in. horizontal 

 web and 2 in. vertical flanges. The laminate should consist of 1 ply cloth on top and 



2 plies mat. 



By separate calculations, not shown, the critical stress is found to occur at the 

 inboard flange of the gunwale. 



Section Modulus, Z, at the cloth = 0.265 in.3 



Stress = Bending Moment f _K_ (2 8) 



Section Modulus h Z 



f t " fi5 =11 >°38psi 

 Ultimate Stress, cloth in tension, F tu = 214,100 psi (Table 5-6) 



Ultimate Stress _ _ _ F tu (2. 9) 



Calculated Stress ' f , 



F.s. = 2 ' ,10 ° = 2.18 Satisfactory 

 11,033 



