BOAT HULL DESIGN 2-57 



Modulus of Elasticity, E mahogany = 1.6 x 10 psi 

 Rigidity (EI) sandwich = Rigidity (El) plywood 

 From Fig. 6 -53a for a Type A sandwich 

 Modulus of Elasticity, E sandwich = 1.95 x 10° 



Required Moment of Inertia, I sandwich = | plywood 1 od ( 2i 34) 



E sandwich r J 



Required I = .0115 in.^ 



Sandwich Section 3/U in. core, 1 ply cloth and 1 ply 

 1-1/2 oz . mat on each face. 



Check longitudinal bulkhead for local load from mast. 



Assumed vertical mast load = 15, 000 lbs. - at breaking strength of stays. 



Assume 9 in. width of bulkhead must withstand load. 



A factor of safety of 2 is used since the load is based on the 

 breaking strength of the stays. 



Consider load on laminate only; core not effective. 



Area of cloth = 2 x .016 x 9 = .288 in. 2 



Area of mat = 2 x .0U2 x 9 = .756 in. 2 



Cloth area equivalent to mat area = area mat x „ > — -,., ■, (9 ?s} 



^ Ec (cloth) v "- °°> 



Cloth area = .756 x * 9 ?/ 10 r = .286 in. 2 (Table 5-12) 



2.J46 x 10° 



Total equivalent area = .288 + .286 = .571; in. 2 



Compressive Stress, f c = — pwj — = 26,132 psi (2 ^3) 



Cloth Ultimate Compressive Stress F cu = 18,900 psi (Table 5-11) 



This is obviously not satisfactory, and cloth reinforcement should be added 

 locally. To determine the required reinforcement: 



Allowable Stress f c = — * = 9,1^0 psi (2. 9a) 



, , 15,000 , t „ . 2 



Required Area = „ j ^ * l.i>3( in. (2 11) 



Required Additional Area = 1.537 - .57U = 1.013 



Required additional thickness each side, t = ^ — 5 '= .056 in. 

 From Table 5-2-4 plies of 10 ounce cloth; t = . 064 in. 

 Add 4 plies of cloth to each side of the bulkhead in way of the mast. 



