BOAT HULL DESIGN 



2-25 



All of the foregoing may sound very difficult, but fortunately it is not usually necessary 

 to perform a detailed analysis on bulkheads except for special cases where large local loads 

 are to be supported. Usually unstiffened 1/2 to 3/4 inch thick plywood for cruising boats 

 and 1/4 to 3/8 inch thick plywood for smaller craft, or lightweight sandwich construction 

 of equal rigidity may be used. This equivalent rigidity is considered necessary since one 

 of the most important functions of a transverse bulkhead is to provide sufficient stiffness 

 to maintain the shape of the hull. 



Ballast Attachment: The attachment of localized heavy ballast occurs in some sail- 

 boats. This ballast, usually in the form of lead or grey cast iron is attached to the bottom 

 of the hull. The attachment is normally made with bolts cast into the ballast and passing 

 through the heavy laminate at the bottom of the boat. The design loading used to check 

 the attachment and the surrounding structure is generally taken as twice the weight of the 

 ballast to allow for acceleration due to heave and pitch. The effect of buoyancy is ignored 

 as an added safety factor. Since conservative design of this attachment costs very little 

 and provides added safety at a vital point, a factor of safety of 4 on the ultimate wet strength 

 of the materials involved is recommended. 



For ready reference a summary, Table 2-2, of the design loadings and factors of 

 safety recommended in this Chapter has been prepared. 



TABLE 2-2 SUMMARY OF DESIGN LOADS AND FACTORS OF SAFETY 



T. denotes watertight. 

 T. denotes non-tight. 



