Nick-

: I agree that if you get everything else "perfect" most failures
: will be somehow related to delamination. While a few of the test samples
: showed sharp, distinct breaks in the fabric and wood, most showed some
: signs of delamination that probably happened before final
: "failure".

Not to beat a dead horse, but is it possible that the delamination is (microscopically, perhaps) initiated by a failure of the core material in compression, and that by selecting a core material of greater compressive strength that delamination might be posponed until greater deflection occurs, and greater strength develops?

: With this in mind we need to think about how to maximize the inter-lamination
: strength. Seems you want a strong bond to the wood, and tight spacing
: between the cloth and wood.

Agreed. My milling experience has influenced my glueup procedures. Milling certain species, I have to take a break after opening up a green log it's so purdy just to gawk. Within a few minutes, though, it changes. Oxidation, or drying, or some combination, I don't know. But I always joint or scuff an edge just prior to gluing to get a fresh surface.Same thing prior to seal coating.

: A strong bond requires good absorbtion of the resin into the wood to maximize
: the adhearing surface area and mechanical grip and the resin having good
: adheasive properties. Epoxy is a good adheasive and this is one reason why
: it is prefered over polyester resin. Not using too fine a sandpaper will
: promote good absorbtion and make a rougher surface for a better mechanical
: bond, but it may also lift the cloth away from the wood more than if the
: wood was smoother. Also feeding the wood resin until it stops absorbing
: will maximize the absorbtion. But, greater absorbtion will increase
: weight.

: I generally recommend a seal coat on the wood before glassing, the downside
: of this is it limits how much resin is absorbed (good for weight, bad for
: strength), it makes it so some of the epoxy-to-epoxy bonding is mechanical
: not chemical, and it will tend to build up a layer of epoxy that lifts the
: cloth off the wood. The problem with skipping the seal coat is it is
: ha26tm to control, as the wood keeps absorbing resin so the cloth may end
: up starved which will produce air bubbles and visible cloth.

: I would also speculate that Mike's idea of using hardwood may result in a
: weaker epoxy-to-wood bond because the hardwood will not absorb the resin
: as readily. But then again, the may just mean that you don't need to worry
: about doing a seal coat at all.

On both boats, I used a seal coat everywhere. I sanded, sealed, the within 18-24 hours, glassed, then filled. All subsequent coats after sealing were done while green, and I thought this was giving me a chemical bond. Is this not the case?

: I'm sure that if someone really wanted to get involved with the material
: science of wood-glass-epoxy composites that there would be a lot of
: factors that would have to be considered to make the
: "ideal/optimum" layup. What I am not so sure about is if the
: "optimum" layup would be a large improvement over a well done
: "standard" layup. I'm sure the standard can be improved upon,
: but when you take into account factors like ease of building, time, cost
: etc, the standard (6 oz glass on 1/4" cedar) works pretty well.

True, and this prompted my Angel on a pin comment. I mean, my best finished work wouldn't make it into the offcut pile of others here. 'Optimum' refers to my next boat, not to anyone else's.

However, there is a small problem. My wife and I are wimps. 5-9/155, 5-3/125. I'm 155, happily. The difference between a 50# boat and a 35# boat is huge to pathetic physical specimens such as us.

The analogy of the wood glass sandwich to the I beam got me through the first boats, but it seems more complicated than that right now. The sandwich is up to five zones: A core of E from 1-2.5x10^6, thin outer glass layers of E about 10x10^6, and two transition layers where God knows what is happening. I'm trying to find a little wiggle room in there somewhere.

Love the boats. The next ones will be better.