Another pre-build, Wood Duck 12 Question

I've especially enjoyed Lazlo's and Twofootartist's build diaries, relating their trials, tribulations, 'inventions' etc.  The posted articles are quite addictive- I spent a couple of hours reading them yesterday!!

 I hope this isn't a stupid question-  Am very interested in minimizing weight and conserving the pricey epoxy.  Along the line of Lazlo's 'orange-crate' stem idea, I'm wondering if anyone has cut wood strips to epoxy in place of so much filleting?  I'd think that with my grandfather's bevel square and my arbor saw, it would be simple, if not a bit time consuming, to cut strips that would fit well.  It seems this would be a good solution for the deck-to-hull joint that's so difficult to reach.  Kind of a mini-chine if you will.

And a final question- why is the sapele decking just 3 mm.  Is it cost? And is it as strong in the end as a 4 mm. deck?

Thanks,

 

              Ross


9 replies:

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RE: Another pre-build, Wood Duck 12 Question

Ross,
Thank you for the kind comments on my blog, www.twofootartist.com
One popular option for the deck/hull joint is to use a wood sheer clamp instead of tape. I think the tape is easier. For the other joints, just keep your fillets small - 1/4 inch radius is probably a minimum. I also find I waste a lot less epoxy by making up small batches, sometimes only an ounce or two, except when I'm glassing.
The sapele decking is heavier than the okuome. Since most of the strength of a S&G boat is in the epoxy saturated fiberglass, the difference in wood strength, especially for the deck, probably doesn't make much difference.
-Wes

RE: Another pre-build, Wood Duck 12 Question

Ross,

Glad you enjoyed it.

The strength of the joints comes from the glass. The fillets just keep the transition between the panels smooth enough so that the glass doesn't peel off. You need that glass and should not leave it off. What Wes said about keeping the fillets small is the best way to economize on epoxy. If you also use lots of thin coats to fill the weave, rather than a few thin ones, and use wooden stem pieces, ytou'll have plenty of leftover epoxy at the end

Don't know why the sapele is only 3mm. You'll have to ask the designer.

Have fun with your build,

Laszlo

 

 

RE: Another pre-build, Wood Duck 12 Question

Lazlo;

 Thanks to you both for the prompt replys.

 Sorry I wasn't clear-didn't mean to exclude the glass, was just referring to the filleting.   Thought the wood would replace the bulk of the fillets; and be able to reach into another foot or so that the arms had trouble reaching.

 Thanks,

              Ross

RE: Another pre-build, Wood Duck 12 Question

If I understand the idea correctly, it is to use shaped wood strip in place of the epoxy fillets to provide a gentle bend radius for the tape, but then to continue normally with fiberglass tape.

I don't know that the work is worth the weight or cost savings, but that isn't your question.

I've not heard of anyone trying it, but I don't see any reason that it wouldn't work.

But there are some big unknowns for me with your approach (related to the great reduction in fillet core strength and stiffness, especially with stresses along the grain) and you should definitely do some test pieces.  Easy way to test them is to drive over them with a car or truck and see where the fracture is.  If it is the same as with the epoxy fillet technique (in the plywood just beyond the edge of the tape) then I think your idea is ok.

RE: Another pre-build, Wood Duck 12 Question

Camper;

 Thanks, liked your test suggestions, think I'll do them, and hope to post the

results.

               Ross

RE: Another pre-build, Wood Duck 12 Question

Ross,

Camper's right. Since the fillets are there just to support the glass, there shouldn't be a problem with the strength of the fillet, especially if the wood strips are epoxied to the hull panels. The big difficulty's going to be getting them smooth enough so that the glass will make the transition across the panels without bubbles, folds or discontinuities. It should be possible, but it'll probably be easier to use putty fillets.

But if you do go ahead with it, do post the results.

Laszlo

 

WD-12 Pre-build, wood strip fillet test

Lazlo et al;

 The test, a 6 inch bond of two Luan pieces with a std. fillet (nickel radius, peanut butter) vs. a triangular wood strip bedded in, was quite interesting.  Whereas it did save about 50% on epoxy weight; it basically showed your fears/suspicions were quite well founded.  I drove over the two, and broke them;  the std. fillet pulled an amazingly uniform, 1/2 in. wide strip of laminate off the complete length of the joint.  The wood strip joint broke along the strip, and showed uneven wetting beneath the strip. Upon reflection, it's not surprising that the strip-joint was non-uniform, since it was not clamped.  So much for a 'good idea'!!! (If I were more 'computer literate' I could attach pics, but I think the words will convey the idea). 

I find that a lot of my 'good ideas' turn out this way when tested.

Just gives me that much more confidence that I can rely on your recommendations!!!!!

 

            Ross

RE: Another pre-build, Wood Duck 12 Question

There's nothing like the scientific method to convince one that the designers knew what they were doing :-)

Well done, Ross. Shame about no pictures, but your description gets the idea across. So now go build your boat.

Laszlo

 

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