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What foam to mold boat from

Old 07-20-2004, 03:59 AM
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Yokomo Aust
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Default What foam to mold boat from

I am going to build my first boat from scratch and have a few questions. I am looking at a mono hull powered by a 540 stock/mod motor and powered by 6-8 cells. I have drawn up the shape to scale and want to know what is the best material to cut it out from. I would like to glass the final product. I was think some kind of poly/styrene but am not sure if the epoxy will effect it. I will make the hull in a top and bottom and join them together i guess.

If anyone has any advice they can pass down to me that would be fantastic.
Old 07-20-2004, 10:14 PM
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Umi_Ryuzuki
 
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Default RE: What foam to mold boat from

Epoxy resin should be fine on foam.

I use the pink(or blue) rigid home insulation from Home Depot.

Something to consider is painting it with latex paint prior to starting your resin layup.
I get a lot of pinholes as the foam degasses thru the resin. I have seen some people cover over the foam with duct tape. They called it a "release agent".

I currently use the foam only in the bow of my build ups. However the possiblities for submarine hulls and other fully foam hull blank sculpts are endless.
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Old 07-21-2004, 10:31 AM
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LtDoc
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Default RE: What foam to mold boat from

Yokomo Aust,
There are basically two types of foam, open cell and closed cell. The 'closed cell' stuff looks like small solid 'beads' of stuff glued together. The 'open cell' stuff looks like foam with millions of bubbles in it. Either will work but do require different techniques in covering/finishing. The closed cell foam doesn't 'absorb' much of anything, sort of like painting wood. The open cell foam, since it is make up of 'holes', usually 'absorbs' more (have to fill all the little exposed holes). There is some 'out gassing' from both types of foam as 'Umi' pointed out, so some type of 'sealer' is probably a good idea.
Another option when using foam as a 'mold' is to cover it with multiple layers of 'glass', then 'melt' out (disolve the foam with acetone) leaving just the 'glass' shell. (The 'big boys' use this technique to build full sized aircraft bodies, EAA, etc.) Makes for a very strong and light weight hull (which does require some internal bracing, maybe.).
Have fun...
- 'Doc
Old 07-21-2004, 07:56 PM
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Yokomo Aust
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Default RE: What foam to mold boat from

Thank you for your replies. I now understand the the surface of foam can be very porous and needs to be sealed before doing my lay up. I also like the idea of using acetone to melt the foam leaving the glass. I was just going to cut it out and leave some in the bottom and front and then glass over that from the inside trapping the foam between the 2 glassed sides.

Thanks Again
Old 07-21-2004, 08:49 PM
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Default RE: What foam to mold boat from

you may want to cut out just the major chunks of the foam and pour little acetone in the formed shell so only the top layer of the foam is dissolved. (Basically carving the full from the inside)
This will thicken the hull giving it extra rigedness and if there are still "intact" foam under the melter layer - boyancy.

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