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Glassing 3/8" (9mm) marine ply?

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hobbsla
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Glassing 3/8" (9mm) marine ply?

Postby hobbsla » Fri Feb 27, 2009 4:59 am

I have a sheet of 3/8" (9mm) okume marine ply that I am using to build a board. It will be a twin-tip, 144x46 or so. My plan at the moment is this:

Top - 3.7 oz. e glass plainweave
Core - 3/8 ply
Bottom - 3.7 oz. s-2 glass

Resin research epoxy.

My question is.......am I over or under building with this plan?

I would appreciate any thoughts you might have.

Thanks.

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Re: Glassing 3/8" (9mm) marine ply?

Postby matthepp » Fri Feb 27, 2009 7:37 am

Yo,
I built almost the same board you are building on my first run.
Pros: really bomber
Cons: It ended up being really heavy, due to lots of resin both in the core and too many extra coats on top. It seems to make for easy planing, but has lots of drag so upwind in light winds are tough. Pearls in the chop with higher wind. 2nd run was much lighter via two stepped sheets of 1/4", shorter but still wide. I did appreciate the learning experience...
Good luck,
Matt Hepp

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Re: Glassing 3/8" (9mm) marine ply?

Postby zob » Fri Feb 27, 2009 12:51 pm

I guess you intend to buy this 3/8'' ply which is much lighter than if you would bond it yourselve with veeners and epoxy.

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Re: Glassing 3/8" (9mm) marine ply?

Postby frankm1960 » Fri Feb 27, 2009 4:01 pm

I don't know. Would you make a flat board or put in rocker or concave?
With only 3/8" ply, if you made it flat, wouldn't it be to flexible even with the glass on it?

My initial thoughts on building a board were to use 1/8" marine ply and 3/8" foam core and
use a vacuum bag system to laminate the ply, foam and epoxy/fiber together with slight rocker and concave. Use something like 3/8" square spruce or pine for board edges so edges can be shaped and also to seal the board. Put in wood inserts for attaching foot straps and grab handle.

Need to find someone with a vacuum table is the biggest problem unless you know how to build one.

We built a light wind board last summer out of 4 layers of 1/8" ply, laminated using gorilla glue and a vacuum table. The board was surprisingly light for it's size. Not much heavier than my LF 151 x 42 proof light wind board. The shape was basically rectangle 162 x 50cm. Laminating the layers I think helped to keep the board from warping.

Good luck with your board.

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Re: Glassing 3/8" (9mm) marine ply?

Postby zfennell » Fri Feb 27, 2009 10:40 pm

it should work fine.
3/8 may be a bit thin, but your too close to let me scare you off.
1/2 definitely works with 4 oz glass.

however, the whole idea of plywood is
is getting good, fast and cheap all at the same time.

so i would shy away from the top shelf items
okume...go for home depot luan
s glass....stick with normal e stuff.
resin research....maybe west or 3m is cheaper (or polyester but it gives me headaches :( )

even cheap plywood can carry more load than good foam, so just use enough glass to carry anticipated flexure loads. (sometimes voids in the wood become an issue but this is cheap, right)

if your want to limit additional weight from too much epoxy, spread a thin coat on the wood before glassing. scrape most off and let it start to kick (judge from some scrap)
then add glass and laminate as planned.

start with the 4 oz per side.
let it cure and test the flex.
if you want more stiffness:
wash lam to remove blush, scuff surface and wipe with alcohol.
add another 4-6 oz per side depending on results.
no worries.

regards,
-bill

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Re: Glassing 3/8" (9mm) marine ply?

Postby hobbsla » Mon Mar 02, 2009 4:27 am

Thanks for all the replies and encouragements! :thumb:

I cut out the board yesterday, here's a pic...
S7300888.JPG


I am planning on putting some rocker in it, about 5 cm or so. Also thinking about staining it to make the wood grain really pop. I read somewhere that if you use water based wood stain instead of oil based wood stain you wont run into issues with your epoxy not bonding to the wood properly.

I am going to do that thin first coat you suggested zfennell, I read a great article from some dude who builds wood kayaks and he seems to have a very good technique for fiberglassing wood. Here it is if any one is interested:

http://www.laughingloon.com/epoxy.html

I think I am going to stick with using Resin Research, it is actually just about the least expensive epoxy the supplier I am going through carries, plus it finishes quite clear which is what I am really after. Does 3 pints sound like enough to do the job?

I am re thinking the fiberglass.... Maybe e glass top and bottom with a patch of s2 glass under the foot pads??

Keep letting me know what you think... I really appreciate the advice! :)

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Re: Glassing 3/8" (9mm) marine ply?

Postby zfennell » Mon Mar 02, 2009 2:52 pm

thanks for the link.
the kayak guys do seem to have a lot of this figured out already.

here's a site you may like fron a company that builds stitch and glue boats
http://www.clcboats.com/shoptips/

regarding the amount of resin to buy.
weigh all the glass you have cut for your project.

a good job bagging would yield equal weight of glass and resin.
doubling the weight of the resin should be a safe margin.

one nice part about epoxy is being able to mix only what you want to work with for the moment and add more as you go.

have fun,
-bill

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Re: Glassing 3/8" (9mm) marine ply?

Postby kitehok » Mon Mar 02, 2009 3:46 pm

I'm guessing this is a lightwind board, you might want to consider less rocker. 2-3cm should be fine.

water based wood stain instead of oil based wood stain

Good thinking, some stains have issues. West Systems did a study, not all oil-based performed poorly, just Minwax.
http://www.westsystem.com/ss/epoxy-adhe ... er-stains/

Don't bother adding extra glass under the feet. I think that's only done to prevent dents on foam cores. 3/8" of wood is strong.

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Re: Glassing 3/8" (9mm) marine ply?

Postby hobbsla » Mon Mar 09, 2009 3:01 pm

Those are some good links!

Kitehok, I'm going to be using minwax water based stain so I was glad to see it passed Wests test. Gives me a bit more confidence that I'm not f'n up my hard work!

Zfennell, if someone on this forum ever puts together a list of useful links for the newbie board builder that one has to be on it! I need all the info I can get. Thanks.

Got my rails shaped, Moving on to the rocker...

Later all.


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