Plywood Moth

[oceangboy2000]

Hey guys and girls, hope everyones holidays are going great. Just a quick question. I was looking over the wooden moth plans supplied on the aus. moth page and am very interested. I did a small experiment last night and was able to bend 5mm exterior luan into the curves the plans call for. I am now wondering if the carbon can be replaced by fiberglass, most likely biaxial? Im not out for a performance machine and if it is possible to substitute the fiberglass for carbon the entire hull could be built for incredibly cheap. Thanks for your help everyone! ~dan

[Chris Ostlind]

For that size of a wooden boat, the difference in weight between a carbon skin and a glass skin is infinitesimal. You can more easily effect the all-up weight by losing a few pounds off your own body or the gear you select to rig the boat.

The weight problem with any small boatbuilding program is not typically in the cloth. It's in the excessive use of the all-too-heavy epoxy. Too much thickened epoxy is the fastest way to kill a lightweight design, so go easy and put it where it belongs and nothing more.

I''d love to see the boat when you're done.

Chris

[oceangboy2000]

thanks alot chris, thats just what i wanted to hear. I am off to the store to get the last of the supplies then. If anyones interested i can put up pictures of how everything goes step by step. ~dan

[Steve Clark]

Uh, half the fun of a Moth is how light it is.
And if you make it too heavy, it certainly won't deliver the buzz.
For VERY little extra money you can get 3mm Occume plywood. Let me guess that the Luan will cost about $15. Occume will coast about $45. So the delta on this project is less than $100. Given the fact that you will spend probably 100 hours building this, why not spend the premium to get the right plywood? It will weigh half as much.
You probably don't have to use carbon. I think there may something in the relative stiffness of the carbon tape relative to an equal ply of glass tape that helps compound the shape, but I don't know.
But once again the amount Phil calls for is less than a yard.....find someone who uses the stuff and look in their dumpster! Or buy it on line for 30 bucks.
Certainly it is a lot easier to justify making the glass substitution if you are already using lighter plywood. Go with the heavy wood and the glass and you might miss the target weight by 100%.
As we discussed in a Trapeze thread below, the hull bill of materials is really a very small percentage of the cost of building a little boat. Assume you are doing this for fun and spend the extra dosh. It is my experience that you will be happier during the process and more pleased with the result.
SHC

[oceangboy2000]

how much does a sheet of 3mm Occume weight?

[Steve Clark]

From the Boulter Plywood site
http://www.boulterplywood.com
3mm- 11 lbs-$39
4mm- 12 lgs- $45

[Chris Ostlind]

"I'm not out for a performance machine and if it is possible to substitute the fiberglass for carbon the entire hull could be built for incredibly cheap."

Not supporting the use of lesser materials, just allowing that it's done frequently and for the personal reasons of the builder. If oceangboy has the funds to go the Okuome route, then he could end up with a better, lighter boat, without question. I'd personally prefer the better materials, but who am I to inhibit the process of self-discovery? I'd be willing to bet that with a little luck in the used rig market and some careful purchases of used gear for the rest of the setup, he could get a very serviceable Moth-style boat out of his efforts and be on his way to one day wanting something better, once the cash is in hand. I wonder how many boats in Australia are built just like this?

Carbon is not going to save as much weight as soem would think. It's resin hungry to fill the weave and that translates to weight. If the boat were being bagged or infused in a bag and all the other factors for weight savings were in place, there'd be some potential there. The total square inches available for any weight savings at all through the use of carbon are miniscule.

Chris

[oceangboy2000]

First, thanks for your input guys. second RIGHT ON CHRIS!! I'm not out to go race at the worlds next summer, heck i dont know where im gonna be next summer. Im finishing my schooling as a naval arch. in may and this project is 100% for me and for fun (nothing to do with school) and to have a boat in service to experiment with. I crunched some quick numbers with the weights amd prices of the occume and yes it will be a lighter hull but the overall goal isnt that, so im not convinced at this stage that its the way to go. Thanks again for your input guys. Anything else you guys have would be awesome to hear~dan

[casavecchia]

Phil Stevenson's plans call for 2 mm plywood and 200gr/ sq.mt. carbon.
Follow the plans.
The one I have built is here.
http://www.moth.it/MarcosCorner.htm
Marco.

[oceangboy2000]

Just out of curiosity where in the world do you get your hands on 2mm ply?

[Steve Clark]

I don't know what "hoop pine" that Phil uses is, but I recall a comment that it was generically heavier than Occume,
1.5mm plywood is available from Boulter.
My guess it that with a bit of glass would be fine.
What I don't know, and Marco can probably tell you, is if the stiffness of the carbon tabbing effects how the panels bend when you compound them. Glass will be more flexible and may not be stiff enough to do the job.
In terms of light ply, if you dig into the wood aircraft supplies you can find almost anything.
Look, I don't like to spend any money either and making that omelet is a career goal. It is up to you, I have just had to rebuild too many thing apart because I "saved" money in the wrong place and they died before they were really used up.
Suit yourself as we say in the provinces.
SHC

[casavecchia]

Yes Steve,
stiffness and taper in the width dimension of tabbing both affect compoundability. Besides being lighter, carbon is better because makes for a fuller hull near the keel line, glass instead will soften chines and keel line thus reducing immersed volume.
2mm okoume plywood is commonly available in Europe.
I don't know why it should'nt in USA.
Marco.

[Steve Clark]

By the way Marco,
Nice job and very clean workshop.
SHC

[Raggi_Thor]

Marco, I hope it's OK that we translate to english :-)
http://translate.google.com/translat...osCorner%2Ehtm

[oceangboy2000]

i went out for some last min. christmas shopping and i come back to all sorts of activity. the comments about the carbon resulting in the proper curves was my initial concern actually, but im glad this whole thing has started. Im actually off the garage right now to make a trial scarf joint in the luan with a new plane i havent used. Once again if anyone is interested in the construction of a moth, from luan, let me know as i am going to go foward with the project to see the results. thanks angain everyone~dan