3-10 



DESIGN DETAILS 



FITTING CONNECTIONS 



All boats have various attachments and fittings which do not affect the over-all strength 

 of the hull, but are vital for operation. This includes engine mountings, chain plates, bitts, 

 chocks, cleats, etc. Certain fittings can put severe local loads on the hull, and these loads 

 must be carefully considered in designing the necessary reinforcement. Loads induced by 

 fittings generally push down on the boat, such as engines and masts; or pull away from the 

 boat, such as rigging attachments and cleats. Horizontal thrusts in one or more directions 

 may also be induced simultaneously. 



Pushing Loads 



The design of engine mounts, mast steps and similar items is basically a problem of 

 providing adequate strength directly under the load to prevent local failure, and spreading 

 the load over a sufficient supporting area. Supports should, wherever possible, be tied 

 into the main structure of the boat, such as, transverse and longitudinal frames, bulk- 

 heads, etc. 



Engine Mounts: A number of typical mountings for inboard engines are shown in Figs. 

 3-28 through 3-33. In each case the longitudinal supports are carried a substantial dis- 

 tance away from the engine, sometimes stopping at a transverse frame or bulkhead, and 

 sometimes tapering down to a normal longitudinal frame. The engine bearers themselves 

 may be of steel or fiberglass angles as shown in Figs. 3-31, 3-32 and 3-33. The loading 

 from the engine is always considered as being supported by the fiberglass laminate, with- 

 out assistance by the stiffener core, if any. It is recommended that a thin layer of neoprene 

 or some similar material be placed between the steel engine bolting supports and the fiber- 

 glass laminate bearers as a means of insulation. Transverse frames are added where 

 necessary to help distribute the engine thrust and weight to the shell, and to reduce shell 

 panel sizes compared to the normal size in the area to avoid excessive vibrations. 



The mounting of outboard engines has been covered in Chapter 2 under transom design 

 since this mounting constitutes a major structural portion of the whole craft. 



Mast Steps: Masts exert major concentrated loads on the boat. Masts may be divided, 

 for purposes of design, into those which step on the deck and those which step on the keel. 

 In wooden construction the keel is a major structural member and can receive the mast, 



NORMAL LONGITUDINAL TO EXTEND 

 FORWARD AND AFT TO TRANSVERSE 

 SUPPORTS 



GRADUALLY INCREASE LONGI- 

 TUDINAL TO DEPTH REQUIRED 

 BY ENGINE 



Fig. 3-28. Engine Mount for Inboard 

 Runabout - Suitable for Low Horse- 

 power Installations Only 



TRANSVERSE WEBS 

 AS NEEDED 



■-CENTERL I NE 



FOR TRANSVERSE SECTIONS IN WAY OF ENGINE BEARER, SEE FIG. 

 3-31 TO 3-33. 



