4-18 



MATERIALS AND MOLDING METHODS 



Si- 



Fig. 4-17. Fiberglass hull of a 40' ketch 

 molded on a male form (Courtesy Jean 

 Fxlloux) 



Bag Molding 



This molding method uses a flexible membrane or bag to apply vacuum or positive 

 pressure to a laminate during the molding operation. 



Vacuum bag molding applies pressure against a laminate by drawing a vacuum under the 

 bag. This molding operation is limited to a pressure slightly less than atmospheric, 14. 7 

 PSI. Vacuum bag molding of boat hulls is currently not being used to any appreciable extent 

 except in the autoclave molding method discussed below. Fig. 4-18 illustrates the flexible 

 rubber blanket in position covering the lay up in the mold prior to placing the entire mold 

 assembly into the autoclave. Pressure bag molding, Fig. 4-19, uses compressed air or 

 steam to force the bag down against the laminate during the molding operation. Pressure 

 bag molding can ordinarily operate at pressures up to 40 PSI. Bag molding operations can 

 readily use heated mold surfaces to produce superior laminates under rapid cure cycles (9). 



Autoclave Molding 



Autoclave molding uses steam to apply a uniform pressure, up to 100 PSI, and heat to 

 the lay up (14). Usually a vacuum is pulled between a bag and the lay up to remove air and 



