BOAT HULL DESIGN 2-47 



h = 5-s/e" 



PORT I ON OF SHELL 

 CONSIDERED EFFECTIVE 



Fig. 2-25. Gunwale - assumed cross -section for horizontal loading 



Transom: As a first trial use the dimensions recommended by the OBC for the over 40 

 horsepower range, Table 2-1. 



Thickness = 1-1/2 in. minimum for entire transom 



Reinforcing at motors 

 Thickness = 2-1/4 in. 



Inboard Area - 10-1/8 in. horizontal dimension 

 - 3-5/8 in. vertical dimension 



Outboard Area - 12-1/2 in. horizontal dimension 

 - 11-1/2 in. vertical dimension 



Use a sandwich construction. 



Plywood core - 1-1/2 in. thick Douglas fir 



Outboard Laminate - 1 ply 10 ounce cloth on aft face 



2 plies 1-1/2 ounce mat against plywood 



Inboard Laminate - 1 ply woven roving on forward face 



1 ply 1-1/2 ounce mat against plywood 



Design on a Strength Basis: For 38 miles per hour - 2 motors at 50 horsepower = 

 100 horsepower. 



Section modulus x Allowable stress _ Z x fij ,_ „. 



Transom Beam B 



From Fig. 2-1?; Z x fi , = 37 

 B 



Beam at transom = 66 in. 



Required Z x ft, = 87 x 66 = 57l2 (2. 6a) 



The portion of the transom considered effective is: The plywood core - parallel 

 horizontal grain plies only; 11-1/2 in. wide; the fiberglass covering for the above width, and 

 the motor well - a strip adjacent to the transom of width equal to 30 times its own thickness. 



The allowable stresses based on a factor of safety of 6, for the various materials are 

 as follows: 



