glassing plywood prior to hull installation

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Scot2640
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glassing plywood prior to hull installation

Post by Scot2640 » Fri Dec 30, 2016 10:39 am

As the title indicates, does anyone have any experience with glassing the individual plywood panels that have been cut to shape prior to actually installing them on the hull?

Do they remain flexible enough to bend?

I'll be using several layers of 3/8" ply (species TBD) and obviously only the final layer will be glassed.

This is the method my designer is recommending. He then indicates to fill the screw holes with glass seam tape and epoxy and then fair the entire hull.

thoughts?
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Re: glassing plywood prior to hull installation

Post by mrintense » Fri Dec 30, 2016 10:50 am

I would not fiberglass before installing the panels. They are going to be difficult in some areas to install and the fiberglass will stiffen the plywood. It will also probably not take the bending too well and separate from the plywood. It's relatively easy to fiberglass the hull after it's completed.
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Re: glassing plywood prior to hull installation

Post by DSR » Wed Jan 04, 2017 9:32 pm

I definitely agree with Carl.

In my experience, cured fiberglass does not have anywhere close to the flexibility needed to be able to be applied in this fashion.I would have to imagine that it would just crack / break / separate from the plywood and lose all integrity if you tried to apply bending or torsional forces when installing the panels.
Even if it could be somehow installed that way, i don't understand what kind of benefit it would provide as opposed to the traditional method of sheathing?

Thanks
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Re: glassing plywood prior to hull installation

Post by gdcarpenter » Thu Jan 05, 2017 4:49 am

I have never tried it that way and don't see any benefits of doing it that way, but that doesn't mean it's wrong. I don't think flexibility would be an issue though.

For floatations I laid fiberglass over an upside down plastic dish pan, then applied the epoxy, essentially making a fiberglass 'shell' that I then filled with expanding floatations foam. I was amazed at how flexible the resulting mold was!
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Re: glassing plywood prior to hull installation

Post by Bill Edmundson » Thu Jan 05, 2017 6:56 am

Scot2640

What boat is this?

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Scot2640
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Re: glassing plywood prior to hull installation

Post by Scot2640 » Fri Jan 06, 2017 6:46 pm

Bill Edmundson wrote:Scot2640

What boat is this?

Bill
41 foot Diesel Duck. George Buehler describes this technique in his Backyard Boat Building book. Although he has never done it, I asked, this is the way he says he would do it if he had to.

I've posted this question on a couple other boating forums and I've had the complete spectrum of responses from absolutely not, to that's the only way to do it! Ultimately I guess it's up to me!

Perhaps when I get to that point, which is still well off in the future, I'll try out a test panel and see how it goes before I commit full scale.

I appreciate everyones input though
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Re: glassing plywood prior to hull installation

Post by Bill Edmundson » Fri Jan 06, 2017 7:32 pm

Scot2640

I think that's the boat that friends of ours live aboard in Gulf Shores AL. Nice boat. I couldn't get a grip on 3 layers of 3/8". I might think long and hard about that method. Glassing that hull in place would be a monster undertaking.

Bill
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Scot2640
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Re: glassing plywood prior to hull installation

Post by Scot2640 » Fri Jan 06, 2017 10:16 pm

Monster is putting it nicely! Gonna be no fun for sure.

Who wants to help?!?
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Re: glassing plywood prior to hull installation

Post by Bill Edmundson » Sat Jan 07, 2017 9:08 am

Scot2640

My wife would love to come up and visit her brother. But, I've developed sensitivity to epoxy. The friends with the Duck, he is allergic to epoxy and Vicky does all epoxy and 2-part coatings work. (Maybe, I'm on to something! :roll: )

Be careful. And use the PPE every time.

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Re: glassing plywood prior to hull installation

Post by Roberta » Sat Jan 07, 2017 10:09 am

I've been thinking about your inquiry for a bit. I know the bigger a boat gets the harder it is to reach around things. I guess glassing the pre-cut panels would work out. I would pre-cut the panels, give each one a seal coat of epoxy, then apply the cloth with one or two fill coats. Once the panels are ready, attach them in the normal manner, fill in the screws, and apply glass tape over the joints and screws. Then continue filling the weave on the tape and panels.

Keep us posted on the progress,

Roberta :D
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Re: glassing plywood prior to hull installation

Post by Nova SS » Sat Jan 07, 2017 10:38 am

I would think you would need to use something after the fiberglass has hardened to clean up the edge of the panel. I would think the fiberglass will likely stretch, somewhat, when you are wetting it out and stick past the edge of the panel. Just my thoughts.

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Roberta
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Re: glassing plywood prior to hull installation

Post by Roberta » Sat Jan 07, 2017 10:54 am

A belt sander and/or a router and trim bit would easily clean up the mating edges of the plywood panels.

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Re: glassing plywood prior to hull installation

Post by DSR » Sat Jan 07, 2017 11:04 am

Hi Scot2640.

I think I have to reconsider my previous post after checking out what you're building. A 41-foot Duck...Holy smokes, I was thinking on an entirely wrong scale..... :D

And all my previous fiberglass experience was with polyester and vinyl ester resins. I remember now that the epoxy resins normally used in boat building are much more flexible than these after cured, so with hindsight now being 20/20, and the scale of your project, glassing the individual panels before assembly may actually be the best way to go....

Thanks
Dave
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Bill Edmundson
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Re: glassing plywood prior to hull installation

Post by Bill Edmundson » Sat Jan 07, 2017 12:09 pm

A RO sander will trim the glass like a knife without touching anything else.

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Dave Grason
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Re: glassing plywood prior to hull installation

Post by Dave Grason » Sat Jan 07, 2017 1:34 pm

I have just now given this thread a cursory overview only. So someone may have already added my thought. But the glassing of panels ahead of assembly does beg the question: "Can we also epoxy the frames ahead of assembly?"

To THIS question the answer is not only YES, but I personally think it's a good idea and I will definitely being epoxying all frames before assembly in future builds. It will be a bit more work on the front end that I believe will save a lot more work on the back end.

I'm just saying.
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