From: racer577@citystar.com
Sender: Star45@yahoogroups.com
Date: Wed, 1 Nov 2006 16:36:47 -0700 (MST)
Subject: Re: [Star45] Re: foam cored hull
We were concerned with having something resembling a one design model with three possible hull materials. There were, at that time, modelers building other class hulls with the exterior being only model airplane shrink wrap plastics and the concern was "what if" the entire framing was covered with mono-coat or some shrink material. I recall this also was one of the reasons that accounts for the hull weight be set at 16oz. Adding foam inside as a foam core plus wood or fiberglass or a combination of wood and fiberglass might make the completed hull a tad heavy??
The foam is light and adds more stiffness than adding a enough glass to get the same stiffness. The CPM deck is a glass with foam layup and at 10 oz or so is lighter than a sheet of 1/16th ply which is not nearly as stiff.
I don't see any specs addressing specifically in the area where the keel bolts are attached, which spreads out the loads associated with this high stress area. How would foam without some sort of glassing or wood lamination spread the high stresses from the keel fin?
The foam gives the glass structure so it isnt a thin flat pc supporting the weight of the keel. With 2 layers of glass 1/4" apart the bottom is very stiff and the load is spread over a large area. Real boats use foam or end grain balsa to do the same thing. Glass is not as stiff as wood. Its stronger, but not stiffer. So when you add a light filler like balsa to give the glass a shape that is stiff, you get a light strong structure.
John
