2-48 



BOAT HULL DESIGN 



Plywood 



Basic working stress - Douglas fir plywood in bending = 2000 psi 



Ultimate stress, F^ u for long term loading = basic working stress 

 x factor of safety on which basic working stress is based (19) 



Fbu 



2000 x 2.25 = 1500 psi 



Allowable stress, f b = hi? 00 = 750 psi 



6 

 T!at in tension at motor well 



(2. 9a) 



Ultimate stress, F-^ 



11,000 psi 



(Table 5-6) 



Allowable stress, f t = 11,000 = 1830 psi 



o 



(2. 9a) 



Multiplying the section modulus, from detailed calculations not shown, of each material 

 by its allowable stress: 



Nat - tension on motor well bottom: 



Z x fj. * 6.26 x 1030 = 11,156 which is greater than 57h2 (2. 6a) 

 Plywood - compression on aft side: 



Z x f h = 10.10 x 750 = 1$16 which is greater than 5'7h2 (2. 6a) 



Satisfactory 



Bulkheads: The critical loading on the bulkheads in this boat is the shear load in way 

 of the cutout under the forward deck. 



Check for shear at Section A-A, Fig. 2-26. 



Use a 1/2 in. core nominal for rigidity. 



Consider all shear load carried by laminate, i. e. core is nonstructural. 



1/2' 



Trc rm i jjy 



SECTION A-A 



Fig. 2-26. Transverse bulkhead 



