Wacky idea: Adding a core to a solid glass boat ?
 

I've got an idea I wanted to bounce off GlassDave and the other experts: has anybody ever heard of a core being retro-fitted into a previously solid-laminated hull ?

I'm considering this approach, here's the situation:

1986 21 foot Wellcraft Scarab 1 outboard. I was looking for a project boat and got it cheap. It's in good shape overall but needs stringers; the transom had already been done and is bone dry. No problem, progressing with that fine, Douglas-fir marine plywood stringers. I'm doing one side of the boat at a time, so 1/2 the stringers are out (it has 4, 2 at 5" tall, 2 at 10" tall). The tabbing on the stringers forms a significant amount of the hull thickness. By that I mean, because the stringers and bulkheads are pretty close together, and very wide tabbing was used, once I ground the tabbing away I've thinned the hull out considerably. I did this knowingly - the tabbing was very poorly done, very wet layup yet lots of air bubbles and some delamination (thanks Wellcraft). The hull was laid up better than the tabbing, but still not great. I found that portions of the (chopper gun and woven roving) hull had bone-dry chop. This was worst along the keel, progressing into the pad, and there was several feet of resulting delamination due to the dry chop. So again, after grinding back to decent glass I again have a pretty thin hull now.

I'm repairing the boat with epoxy and 1800 double-bias. I have a lot of experience with epoxy and have built my own WEST-construction cat/tunnel before.

Here's the idea: rather than lay up a ton of glass to re-build the bottom, why not vacuum-bag in a core and additional skin inside ? That would give me a MUCH stronger and stiffer bottom than I originally had (I think the original hull is a little over 3/8" thick). I don't think it would be that much additional labour since the most I could lay up right now is 1/8" at a time (4 layers of 1800). It might save me money too since building up that much bottom thickness would get spendy with epoxy even though I have been getting it at wholesale. The weight savings are obviously a bonus too (this boat was heavy to begin with). If I can verify the remaining hull thickness (I believe it to be around 1/8"), I was thinking of vacuum-bagging in 1-2 layers of epoxy/1800, then probably 3/8" or 1/2" balsa bedded in thickened epoxy, then another 4 layers (approx. 1/8") of 1800 to approximately balance out the skin thickness. I'm planning to use an ultrasonic thickness tester or coatings scanner to measure the remaining thickness accurately.

Am I completely nuts ? I like the boat and am intending to keep it long-term. It will have big power and I want it to be really strong when I'm done with it. Not a problem if it's not in the water this year, I'm content to take the time necessary to do it right.

Matt

Nothing wrong with that idea at all. I had an old Omega daycruiser (24 Hawaiian splash) that suffered from a dangerously thin layup and considered that idea as well. I ended up going a different route with that one but with proper prep and technique i think you'd be headed in the right direction with you goals. Your already using an advanced system that will allow you to build on the light side so you can keep additional weight down and properties up. When you say 1800 is it a 0/90 or 45/45 bias?


and yeah . . . . your nuts . . . . but for the same reasons as the rest of us :D

Thanks Dave, I really appreciate the vote of confidence. I've learned a lot from reading your posts (been lurking on here for some time). It's a 45/45 bias, I'll be using a fairly low viscosity laminating resin.

Matt

I'm no expert but I wouldn't use balsa.

Yeah, I know balsa is kind of controversial. But if builders like Skater and Progression are using it I think it's good enough for me :) In all seriousness, I am considering some foams - they have come a long way. Not sure yet.

Matt