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Old 01-02-2014, 19:15   #16
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Re: Plywood for core

Rain Dog is drinking whiskey, smokin a cigar, and shooting the breeze with a neighbor in the cockpit right now :-). So I'll try to answer for him.

The water infiltration must of been through the hinges, but it is complete saturation. The hatch is so well glassed that any water that gets in does not get out. It is a beautiful glass job, very very thick, would hate to cut out all that beautiful glass( yes, I'm talking about the underside). I will post pictures tomorrow when the sun is up.

I cannot find minuret post that was referred to earlier, can you send me a link? Idylles, will check out your site thanks for the great info.
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Old 01-02-2014, 19:41   #17
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Re: Plywood for core

Might try MDO it's used for exterior sign boards void free exterior glue etc... Cheaper then marine grade and quite good if well sealed
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Old 01-02-2014, 20:33   #18
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Re: Plywood for core

Quote:
Originally Posted by RainDog View Post
Sounds expensive, but I guess it is still cheaper than buying a whole sheet of marine ply.
The cheap but similar alternative is polyester resin and balloons - but you have to be fast with the short work time. The 635 thin resin I noted previously takes days to cure. Polyester - minutes. Work the balloons into the resin before catalyzing. I would never do this below the water line but hatches are fair game.

I did this on locker lids and the lazerette cover that were glass - wood - glass sandwiches. Wood was rotted crud. I burrowed in from an edge using a 1/2 inch spade drill with extension. I was able to hollow it out by removing most of the wood and then refilled using resin & fillers. The visible outer never was effected.

BTW the builder buried aluminum backer plates inside the structures for hinge attachment. These corroded and expanded - the source of water entry.
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Old 01-02-2014, 20:49   #19
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Re: Plywood for core

Polyester resin takes a range of appropriate catalyst ratios and can be mixed so as to have a long pot life. I am using it in 90F temps right now and can keep it alive in the pot for an hour or more.

Mixing the balloons before adding catalyst is bad advice. Don't do that - catalyze it first, then mix in the balloons or fumed silica or whatever.

There is no need for marine ply in your application. Exterior ply is minimally necessary because you do want waterproof glue. Voids are of little concern to you. If you have 1/4" skins on each side, the core itself is of little concern to you. The advice above about some inexpensive polyester resin and microlite filler is fine (just catalyze before mixing). Mix it up thick and stiff and trowel it in. If you use the lightweight stuff, you should have large volume and low weight - make sure it is whipped up and not runny because the resin isn't doing much for you here other than keeping the microballoons in a matrix.

However, if you are anywhere near a marine materials supply place or boat building/repair place, you can probably score a bit of balsa, structural foam or honeycomb for not much money.

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Old 01-02-2014, 20:54   #20
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Re: Plywood for core

I find this discussion amazing. Do you know what a pain it is to recore fiberglass? How much time it takes? And you want to save maybe $40 dollars on the new core so that it can fail and you get to do this again?

Really?

Get the meranti, or some kind of rigid foam. Pay the price, and never worry again.
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Old 01-02-2014, 21:01   #21
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Re: Plywood for core

1/4" fiberglass on either side plus 3/4" ply? You guys buy a Westsail now or something?
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Old 01-02-2014, 21:12   #22
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Re: Plywood for core

Use Coosa board in the appropriate thickness with G10 or similar blocks for the hinge fasteners to tap into. Costs the same as ply and will last longer than you. You can get it in half sheets (big money saver). It's a dream to work with. Poly resin sticks to it extremely well with no prep, though I scratch it up on general principle of course. I use a lot of Bluewater 26, but there are options. You can of course skip the G10 if through bolting instead is an option, but it often isn't. You can also use a block of aluminum in place of G10, or even bronze(heavy), but these should be well glassed in and I prefer G10.


Coosa Composites, LLC - Manufacture of high-density, fiberglass-reinforced polyurethane foam panels




http://www.fisheriessupply.com/coosa...s-marine-board





http://www.eplastics.com/G10_FR4_Glass_Epoxy_Sheet
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Old 02-02-2014, 06:58   #23
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Re: Plywood for core

Minaret, I haven't worked with coosa before, but everyone raves about it. You can't screw into it? It seems like it is dense enough to hold a screw - particularly since that screw would be going through 1/4" of fiberglass first.

Rather than bothering with the G10, for this application is it simpler to just mix up some chopped strand and cabosil and fill the small hinge cutouts.

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Old 02-02-2014, 09:40   #24
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Re: Plywood for core

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Originally Posted by colemj View Post
Minaret, I haven't worked with coosa before, but everyone raves about it. You can't screw into it? It seems like it is dense enough to hold a screw - particularly since that screw would be going through 1/4" of fiberglass first.

Rather than bothering with the G10, for this application is it simpler to just mix up some chopped strand and cabosil and fill the small hinge cutouts.

Mark


Coosa will tell you you can tap into it, and you can. But it ain't wood. Higher torque settings on a cordless clutch may strip out your tap, and due to the friability of foam I don't trust a fastener done that way to last through repeated load cycles. I would not tap fasteners into chopped strand and cabosil either. Too brittle. G10, however, is excellent for tapping. Just make sure to start with a regular tap and finish with a bottoming tap. Plus filling a hinge sized cutout in 3/4" material perfectly is a pain, you will have exotherm problems and have to do multiple fills. This means the G10 pays for itself. I make my own.


I actually just did some hatches without solid blocking for the hinges, in Bluewater 26. Tapped into the Coosa as you are suggesting, it's sort of an experiment(by request). But there are mitigating factors in the install. I'll be interested to see how long it lasts. Probably be fine due to the way it's built, but I wouldn't slap the usual ten year warranty we do on our work on it. If you build as I'm suggesting, it will last forever. The Coosa rep told me they submerged sample pieces in seawater for two years, and they absorbed less than one tenth of one percent by weight. Wet core will never be an issue, even if water gets in there the core will not absorb it.
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Old 02-02-2014, 10:05   #25
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Re: Plywood for core

Here, you do it like this.


First, throw the original hatches away. They are usually warped, cracked, poorly built and poorly fitted. More trouble than they are worth. Then finish the hatch coaming to primer stage. Then shim for patterning. In this case, the door skin shim allows room for the thickness of the glass which will be added to the part, and the stir stick shim allows room for the final gap.
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Old 02-02-2014, 10:06   #26
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Re: Plywood for core

Then pattern.
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Old 02-02-2014, 10:09   #27
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Re: Plywood for core

Cut your parts. Coosa cuts nice with regular tools, but carbide abrasives are better. Suit up, it's itchy!
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Old 02-02-2014, 10:13   #28
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Re: Plywood for core

Bond on the trim edges in place to be sure your angles are perfect. You can bond using Rage or any other poly product. This makes it super fast and easy to do, no waiting for epoxy cure times. Don't forget to shim for height too! This is 3/8" Coosa for edges.
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Old 02-02-2014, 10:15   #29
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Re: Plywood for core

Radius and scuff to prep for glass.
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Old 02-02-2014, 10:18   #30
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Re: Plywood for core

Glassing. Schedule on these is two 1.5 oz. matt and two 12 oz. 0/90 on exterior skin. Interior is a matt and a 10 oz. boat cloth. All in e-glass and poly. 0/90 pictured.
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