What side to glass?

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Fuzz
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What side to glass?

Post by Fuzz » Tue Nov 14, 2017 4:19 pm

So I have been reading the thread about foaming under the deck to stiffen it and got to thinking, could be bad :lol:
With a cored deck you want glass on top to protect it but the glass on the bottom is the glass under tension and is what makes the deck stiff. If this is correct then it seems to me the bottom glass is more important than the top glass. If this is wrong please explain to me what I have missed.



Jaysen
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Re: What side to glass?

Post by Jaysen » Tue Nov 14, 2017 4:25 pm

Since you asked, I think this is where you went wrong.
Fuzz wrote:
Tue Nov 14, 2017 4:19 pm
... and got to thinking...
Everything else make sense.

Fuzz
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Re: What side to glass?

Post by Fuzz » Tue Nov 14, 2017 4:31 pm

I thought you were supposed to be molding something for the boss.

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Re: What side to glass?

Post by Jaysen » Tue Nov 14, 2017 4:33 pm

Until she wins the lotto I still have to do this thing called "go to work". Luckily for me that is mostly just sitting around looking at BBC forum for new opportunities to harass you.

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Re: What side to glass?

Post by silentneko » Tue Nov 14, 2017 4:37 pm

I don't think any cored deck is designed to be used under real tension, and needs to be properly supported to eliminate flex. The glass on top is required to protect it, the glass underneath is optional in a lot of builds. The best scenario is the deck is resting on foam meaning no flex at all, if so no bottom glass is really needed I would think. That being said, I always glass both sides as checkin seems to happen even with great plywood.
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cape man
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Re: What side to glass?

Post by cape man » Tue Nov 14, 2017 4:38 pm

As I understand it the glass on top of the deck (or any surface taking traffic or gear) is there to create a barrier for the wood. Ding the glass and you still don't have penetration into the wood - i.e. water in the wood. Underneath, no traffic, no gear, no dings, no need for glass. When people talk (including me) about the foam stiffening up the boat, it's the hull, not the deck. The bond that stuff makes between the stiringers and bulheads, and to the bottom is very strong and ties everything together.

The ply for the deck should be stiff enough in and of itself to not flex significantly, especially when glued to the stringers and bulkheads. In another thread here I advised against using 1/4" for the deck because of that.

Like I said...As I understand it...
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Re: What side to glass?

Post by jacquesmm » Tue Nov 14, 2017 6:21 pm

For stiffness when you walk on it, the bottom layer is the most important. That will work in tension.
Now, the decks are designed to be stiff enough without any glass on either side but many like to put a thing layer of glass on top for protection. It adds very little stiffness.
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Re: What side to glass?

Post by fallguy1000 » Wed Nov 15, 2017 12:12 am

I don't have much choice; have to glass both sides of the foam or it'll get real saggy.

But you are pretty much correct. The better support would be from underneath; only plywood doesn't need that much xter. So, a top layer gives you abrasion protection. The other thing is if you want to avoid ingress; putting fiberglass on top also helps you create the bathtub effect.
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Re: What side to glass?

Post by Fuzz » Wed Nov 15, 2017 2:53 am

The hardtop I am building is 5x8 out of 3/4 inch nidacore. With one layer of 1708 on one side it would bow a ton just from its own weight. Put a layer on the other side and it is a whole different story.

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Re: What side to glass?

Post by fallguy1000 » Wed Nov 15, 2017 8:43 am

I think most of us were thinking supported deck sole.

I'd do both sides of the hardtop.
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