4-14 



MATERIALS AND MOLDING METHODS 



Commonly used materials for stiffener and sandwich panel cores in boat hull construc- 

 tion are wood, foamed plastics, honeycomb, and lightweight plastic spheres embedded in 

 resin, Fig. 4-11. 



For stiffeners, in addition to the full core materials, cores of hollow rectangular 

 aluminum tubing and half round paper tubing, cut to fit the hull form, are also being used 

 (6,7). 



/ Z 



\ 3 



\ 4= 



Fig. 4-11. Low Density Core Materials - 1. Balsa Wood, 

 2. Polyurethane, 3. Honeycomb, 4. Polystyrene 



Wood 



Various types of wood such as hard woods, plywood and balsa have been used as core 

 materials. Experience has indicated that solid hard wood cores, encased in the laminate, 

 have a tendency to swell and thereby crack the laminates covering them, causing water 

 penetration. Both waterproof plywood and balsa wood cores have proven satisfactory, 

 balsa wood being used more frequently (23). 



Foamed Plastics 



Rigid unicellular prefoamed or 

 foamed in place plastics (5) are pri- 

 marily used in fiberglass boat con- 

 struction to provide buoyancy by 

 filling hollow spaces under boat 

 seats and other locations, Fig. 4-12. 

 Unlike cork, kapok and other ma- 

 terials, foam plastics will not decay 

 or become water-logged. Pre- 

 foamed polystyrene and foamed in 

 place polyurethane plastics are 

 generally used as buoyancy ma- 

 terials. Polystyrene foam, unless 

 properly coated to prevent contact, 

 will be attacked by resins containing 

 liquid styrene. 



Fig. 4-12. Lifeboat with foam for buoyancy 

 (Courtesy V. Chance Associates) 



