DESIGN DETAILS 



3-21 



nuts on bolts are pulled up too tightly. For these fasteners, an insert or build-up of solid 

 fiberglass laminate should be used to replace the lightweight core material. Fig. 3-47 

 indicates this insert construction. Plywood, hard wood, filled resin, and metal inserts 

 have been used, but are not recommended. 



An alternate method for the attachment of fittings is the use of a through bolt with a 

 special sleeve. This construction is shown in Fig. 3-48. The sleeve is used to increase 

 the bearing area, and to provide a spacer so that the sandwich core cannot be crushed by 

 indiscriminate tightening of the nut. Local reinforcement of the skins to increase bearing 

 area may be necessary. 



The attachment of heavily loaded fittings to sandwich construction can be accomplished 

 by the use of through bolting, combined with solid fiberglass inserts or build-up between 

 the skins. The solid fiberglass insert or build-up should be made as large as required to 

 distribute the load over a greater area of the sandwich panels. 



UPPER SKIN 

 OF SANDWIC 



MOLDED-IN OR PRE-MOLDED 

 F I BERGLASS I NSERT I N 

 WAY OF THREADED FASTENER 



CORE MATERIAL 



LOWER SKIN OF 

 SANDWI CH 



CORE MATERIAL 



SANDWICH SKINS 

 LOCALLY REINFORCED 

 FOP INCREASED BEARING 

 STRENGTH IF NECESSARY 



METAL 



SPACER SLEEVE 



Fig. 3-47. Fiberglass Insert for Threaded 

 or Bolted Fastener in Sandwich Construction 



Fig. 3-48. Through Bolting in 

 Sandwich Construction 



TROUBLE CAUSING DETAILS 



This Chapter has endeavored to show recommended construction details. The 

 importance of good design details cannot be over-emphasized, since many of the difficulties 

 experienced with fiberglass boats in the past can be traced directly to the use of improper 

 details. Improper details can be easily corrected before construction but are very diffi- 

 cult to correct after the boat is built. No list of "things not to do" can cover all the 

 possibilities, but a discussion of the principal classifications of trouble causing details 

 should enable the designer to avoid major difficulty. 



DEFLECTED SHAPE OF FLEXIBLE PANEL UNDER 

 UNIFORMLY DISTRIBUTED TRANSVERSE LOAD 

 NO STIFFENING - NO HARD SPOT 



■RIGID ST IFFENEP 



DEFLECTED SHAPE OF FLEXIBLE PANEL UNDER 

 UNIFORMLY DISTRIBUTED TRANSVERSE LOAD 

 WITH RIGID STIFFENEP. NOTE ABRUPT CHANGE 

 IN DEFLECTED SHAPE AT END OF STIFFENER 

 WHICH CAUSES HIGH STRESS CONCENTRATION 



Fig. 3-49. Hard Spot Due to Abrupt Ending of Stiff ener on Shell 



