Hey, David-
: I love these types of ROS theory sessions. I get them a lot, but always
: thought it was because I wasn't staying busy enough with my hands.
Me too. I get really scary when I'm varnishing.
: I like your theory on less wood by using hardwood more strength less
: glass/epoxy and weight. But the less stiff more flex is not true at least
: to the point we can make use of it. The epoxy bonds the glass thus taking
: away its ability to flex and give with a blow, instead it seperates at the
: point of contact or delaminates.
My gut feel is that the likely cause of separation at the point of contact is more or less influenced by the compressive strength of the core material. If the core material is better able to resist compressive failure, either by avoidance (flex) or simply by being stronger in compression, then separtion won't happen. I seem to remember that Vaclav's site had a comparison of epoxies, and that as a rule slower curing epoxies retain greater flexability than faster curing ones. I think you are right on this point, though, and it is my area of least understanding. I do know that on the new boats, the deck (with the 4 oz glass) deflects noticably when pushed hard, but the 6 oz hull doesn't move much.
: A quick study on the SOF boats will educate us that we cannot use paint or
: varnish on the dacron covering as it will be reduced in strength by as
: much as 80% due to this bonding of the fibers.
So is the dacron weakened chemically, or is the skin weakened due to it's lessened ability to "give"? This is kind of what I'm trying to get to with the cubic function of the deflection in the half-thickness core.
: I am presently making laminated bows, 3 or 4 wood laminations and 2
: laminations of glass all bonded with epoxy. Stiffness is controlled by
: either thickness of laminations or number of laminations while keeping the
: glass constant.

: I am a big believer in the I beam comparison for bows and stripper boats. In
: the kayaks we have something else going, the shape of the boat like an egg
: is very strong.
The I beam comparision is questionable on at least one point, IMHO. A typical I beam of steel is homogenous, and has the same strength in tension as in compression. Wood, on the other hand, is certainly not homogeneous, and is substantially stronger in tension than compression. I don't think the core of the sandwich (wood) is acting like the web of a steel beam to a great degree. Your point of the bonded epoxy is important, and I think complicates the analysis of what is going on there.
Mike