BOAT HULL DESIGN 2-45 



Assume adequate bond between core and faces and that core is not 

 effective in flexure, the section modulus is: 



Section Modulus, Z = (2. 26) 



6 h 



z __ 1 x [Q.32U3 - q.253] = ^016 = ^ .^3 

 6 x 0.32a 1.9UU 



1 U9 

 Stress in facings, f„ = * „ = 165.6 osi 

 ^ .009 



Maximum Shear: V = -^ (2.24) 



2 



V = 0.26 x 8 = 2.2U lbs. 



Shear Stress in Core, f„ = 2 V (2.27) 



' s 2 A 



f - 2. 21; . 



f s " 2 X Ix .25 = 13 ' 5PS1 



Required ultimate core shear stress = f„ x F.S. 

 = 13.5 x 1; = 5U.0 psi Satisfactory 



The 1/4 in. thickness is chosen as the minimum for workability. The core material 

 may be of any of those discussed in Chapter 4, with preference given to a solid material 

 which will be able to resist the shear loads and high local impact loads as would be caused 

 by a person jumping into the boat, or heavy objects being dropped on deck. 



If desired for appearance reasons, a ply of 10 ounce cloth may be added to the top of 

 the deck sandwich. Caution should be exercised to avoid too smooth a surface in walking 

 areas for safety reasons. 



Deflection Check: As explained in Chapter 6, a conservative estimate of the deflection 

 of a sandwich section is the sum of the bending deflection of the faces alone plus the shear 

 deflection of the core alone. 



Pt^ 6Pt 2 



Deflection, d = — + — — (2.28) 



38U E f I f 5GcA c 



Assume a cellular cellulose acetate (CCA Foam) core 

 of 6 lbs per cubic ft. density 



Shear Modulus, G c = 1.25 x 10 3 psi (Table 5-17) 



Area of Core, A c = 1 x 0.25 = 0.25 in. 2 



_ 0.28 xjj + 6 x 0.28 x 8 2 



38h x 2.06 x 10 6 x .009 x .321 !40x 1.25 x 103 x 0.25 



2 



= 0.001 + 0.016 = 0.017 in. 



Allowable deflection, d = — = — = O.OI4 in. Satisfactory 



200 200 



