glassing plywood prior to hull installation

[UNCIVILIZED]

Lotta good points on the negatives of glassing the panels first. But I've a few to add.
First, if you glass them prior to using them to build the hull, then all of the bonds that you make to & with them will be 2ndary ones. Which are a lot weaker than are ones made with epoxy that's uncured, or green. As such bonds as chemical as well as mechanical. And this weakness is even greater if you don't get all of the amine blush off of the cured epoxy in the panels.
Yes, the bonds will probably be strong enough, but why give up so much strength before you really get started?

Next, if the panels are pre-glassed & you're trying to bend them into a hull, then there will be large stress risers at every joint where a panel meets it's mate.
Also, it'll be pretty dang tough to try & do scarf joints of the panels this way in order to alleviate some of this. And butt joints are far from ideal.

Then, if the panels are butt joined, you'll also have to add additional cloth or tape at each joint. Which will created raised seams everywhere, so that you'll need to do a lot more fairing work, & also use a LOT more fairing compound. Which is both heavy, & expensive. Not to mention that it's a bitch to sand, & get fair as well as smooth. So it's a lose, lose, lose, all the way around.

Also, to some degree it sounds as if you want to glass (or epoxy) each layer of your 10mm panels prior to applying them. Which doesn't make the most sense to do in between layers. At least from a bond strength standpoint. Since you'll be using a lot of extra epoxy in doing so as compared to just epoxying two clean (virgin) layers of wood together. Plus, again, you'll be adding; weight, & expense. As well as creating secondary bonds again.

In theory you'll add some strength & impact resistance to the hull by doing this. But unless you've done some testing of different panel layup schedules, it doesn't make sense to go this route.
If memory serves, there's some info on examples of the strength of a few different panel layup skeds in the book The Gougeon Brothers, On Boat Construction. Which you can download free at the WEST System site if you haven't already done so. And another source of examples is to be found in Bill Lee's writeup of the sailboat Rocket Science. Who's owner is a member here on CF. She's a Riptide 55' by NA Paul Bieker. Technical Details | The new Adventures of s/v Rocket Science
One other info example of panel testing is in Professonal Boatbuilder magazine, about the construction of the boat s/v Jelik, by Schooner Creek Boatworks in OR. She's a Wylie design IIRC. They created & had a dozen+ different types of panel layups prior to settling on one to build her out of.

There are of course more pro's & (mostly) con's to going the route that you're describing, but they're not springing to mind at the moment. But either way, you'll be doing yourself a favor by studying on this a bit prior to building. Meaning studying more on construction, composites, etc.

Pretty much all suppliers of epoxy, reinforcements, cores, etc. have lots of free info on these topics. Which, as with most things, it's wise to study & cross check your info material via studying it from several different sources. That way you better rule out "learning" crap ideas from any one particular idiot, as is unfortunately common thanks to the internet.

Look at it this way. If an epoxy manufacturer, or a (published) writer puts out a product & info on that product which is crap, then word of this spreads & no one buys their stuff. So they go broke, & (hopefully) take the bad materials & info to the grave with them.

[jimbunyard]

Originally Posted by scott2640

As the title indicates, does anyone have any experience with glassing 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?

The question is really too general to answer with any specificity.

Certainly you can glass one side of 3/8' plywood and bend it enough to install on most, if not all, curves on the hull of a 41', hard chined trawler.

I can even sort of see the logic, if you were, say, glassing the inner surface before attaching it to the frames, to simplify construction and to initially seal the inner skin, which would be much easier (not to mention efficient) than trying to glass in individual patches between frames, stringers and bulkheads.

We need more information about your construction method, what you're trying to accomplish, and details of materials and construction to make any remotely accurate recommendations or form any opinions...

Many, many boats have been constructed with isophthalic polyester (or worse) resins and wood and have been very fit-for-purpose indeed.

There are blush-free epoxy resins available, I've used some of them but have not yet come to any conclusions about them.

Regarding pre-glassing construction panels, such as bulkheads or the like,
I've done it quite frequently with excellent results. As noted though, thin panels of any sort are likely to have warps induced if you try and glass one side at a time. This can be alleviated largely by coating both sides simultaneously with resin, and then glassing the panels after the seal coat has kicked. Or just don't use thin panels (3/4" plywood hardly distorts at all), or only glass the panel after it has been cut to fit...

[Lepke]

In the 70s I built a PT style hull with plywood. The completed hull was then glassed. I built it upside down then later rolled it. Plywood was treated with pre-EPA wood preserver. Boat is still around.
The butt joints need to be sharp angle cuts to better bond and I used epoxy between plywood layers for hull strength and to stop any water or rot at the inside or outside layer. Plywood seems to rot better than any wood I have used.
Now when I use plywood, after cutting, I paint the edges with thinned epoxy as a primer. Sometimes the whole piece.

[pdenton]

somebody here has dozed during mechanical engineering class.
If you been awake you'd know the ccoefficient of thermal expansion is different for polyester resin than wood. Delamination happens sooner or later. Not only does epoxy resin have the same coefficient of thermal expansion as wood, but it is much stronger and more flexible. It is easier to use and does not have toxic fumes.
polyvinyl ester is the worst of both worlds. It's almost as expensive as epoxy and the laminates hold up. BUT nothing else will stick to it, including itself if the primary layer has hardened.
To answer the original question, matter what I'm making a skiff or a larger boat,I always fiberglass both sides with let's say 10 ounce cloth. You waste some material this way but it is so so much easier to use.
Please do not waste your money buying epoxy from West Marine. Raka in Fort Pierce FL sells epoxy in many mix and match combos along with fiberglass ( I do love the tri- axial matte.
I am not asking you to believe me, I'm asking you to find references to support or disprove what I'm saying. If you have to ask these questions, reaping in anecdotal evidence, you are not in a position to start building a boat. Making the wrong choice here is not like deciding which anchor to buy.
pdenton
pdenton

[anacapaisland42]

We epoxied the whole 4x8 sheet before cutting, it was amazing how much of the epoxy was utilised ... made life a lot easier...would recommend doing that.
Bill

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?[/QUOTE]

[captlloyd]

Originally Posted by pdenton

somebody here has dozed during mechanical engineering class.
If you been awake you'd know the ccoefficient of thermal expansion is different for polyester resin than wood. Delamination happens sooner or later. Not only does epoxy resin have the same coefficient of thermal expansion as wood, but it is much stronger and more flexible. It is easier to use and does not have toxic fumes.
polyvinyl ester is the worst of both worlds. It's almost as expensive as epoxy and the laminates hold up. BUT nothing else will stick to it, including itself if the primary layer has hardened.
To answer the original question, matter what I'm making a skiff or a larger boat,I always fiberglass both sides with let's say 10 ounce cloth. You waste some material this way but it is so so much easier to use.
Please do not waste your money buying epoxy from West Marine. Raka in Fort Pierce FL sells epoxy in many mix and match combos along with fiberglass ( I do love the tri- axial matte.
I am not asking you to believe me, I'm asking you to find references to support or disprove what I'm saying. If you have to ask these questions, reaping in anecdotal evidence, you are not in a position to start building a boat. Making the wrong choice here is not like deciding which anchor to buy.
pdenton
pdenton

Sound advice here. There is a lot of information on YouTube and books on plywood boatbuilding on Amazon. I agree, you need to get up to speed information wise before you drag out the saw.

[jimbunyard]

Originally Posted by pdenton

somebody here has dozed during mechanical engineering class.
If you been awake you'd know the ccoefficient of thermal expansion is different for polyester resin than wood. Delamination happens sooner or later. Not only does epoxy resin have the same coefficient of thermal expansion as wood, but it is much stronger and more flexible. It is easier to use and does not have toxic fumes.
polyvinyl ester is the worst of both worlds. It's almost as expensive as epoxy and the laminates hold up. BUT nothing else will stick to it, including itself if the primary layer has hardened.
To answer the original question, matter what I'm making a skiff or a larger boat,I always fiberglass both sides with let's say 10 ounce cloth. You waste some material this way but it is so so much easier to use.
Please do not waste your money buying epoxy from West Marine. Raka in Fort Pierce FL sells epoxy in many mix and match combos along with fiberglass ( I do love the tri- axial matte.
I am not asking you to believe me, I'm asking you to find references to support or disprove what I'm saying. If you have to ask these questions, reaping in anecdotal evidence, you are not in a position to start building a boat. Making the wrong choice here is not like deciding which anchor to buy.
pdenton
pdenton

Ah.... if it were quite so simple...

Some 'coefficients of thermal expansion':

(10-6 m/(m K))*)

Unfilled epoxy 45-65
Southern pine 5
Fiberglass filled polyester resin 25

As noted previously, details are important.

Not only that, but wood has substantially different coefficients across the grain as opposed to with the grain.

In my experience, delamination always happens eventually when applying resins to wood; the key to keeping things kosher is keeping water and wood separate. That means scrupulous attention to detail; thoroughly wet- out laminates, no voids for water to find and migrate through, and meticulous, timely repair to any breaches in the protective layer of glass skin whether it be the highest tech epoxy/carbon/Kevlar laminate or lowly boatyard resin and ounce and a half mat.

[mitiempo]

Originally Posted by scott2640

As the title indicates, does anyone have any experience with glassing 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?

If you glass the panels before installing you will end up with secondary bonding between the panels unless you install very soon after glassing. Secondary (mechanical) bonds are nowhere near as strong as primary (chemical) bonds. I do not see any advantage and a lot of negatives. I wouldn't do this. I also do not know of any large boat where this was done, because it adds labor, cost, and really makes little sense.

I would use epoxy - not only is it more adhesive but it will resist moisture absorption over time much better than polyester. Polyester hulls are barrier coated with epoxy - not the other way around.

[darylat8750]

I would be inclined to follow the designers instructions. I assume this is a George Bueller design and he has built many of his own designs himself. If you bought the plans from him he will answer questions and take the time for discussion if you are puzzled. On a big boat built by an amateur some times the perfect engineering solution is trumped by what you are able to accomplish in your back yard.

[Fore and Aft]

As a marine surveyor I have seen more plywood/polyester resin failures than I can count. The best ones are where you can just peel sheets of the glass of the plywood......saves grinding LOL
I only preglassed the bottom panels on my Volkscruiser because they were going to be to hard to glass once in posistion.

Happy sailing

[ramblinrod]

If you glass the panels before installing you will end up with secondary bonding between the panels unless you install very soon after glassing.

This is definitely true of epoxy. Not true of unwaxed polyester, where one can come back in a couple days, or even up to 2 weeks later, and continue the lay-up.

I would use epoxy - not only is it more adhesive but it will resist moisture absorption over time much better than polyester.

Polyester hulls are barrier coated with epoxy - not the other way around.

To each there own.

First, if the polyester resin / wood bond, is as strong as the wood itself, how can one gain better adhesion?

Second, I use Isopthalic polyester resin (especially under the waterline) which is quite impervious to water and structurally stable. It is about half the cost of epoxy (though this has absolutely no bearing on my reason for using). I've never had a blister issue for any of my repairs, so how would "more impervious" benefit.

Third, if one is going to apply barrier coat anyway (and I recommend it whether using epoxy or polyester), just how impervious does the FRP laminate have to be?

Some of these arguments are similar to...

"Voltage drop is bad; the heavier the wire, the less the voltage drop; so use 4/0 cable for all instrument wiring."

For electrical wiring, as with resin, there comes a point where improving the properties of the component makes negligible difference to performance of the system. So if polyester has many advantages over the (supposed) "superior adhesion" of epoxy, then the polyester resin may actually be the better choice.

[ramblinrod]

Originally Posted by Fore and Aft

As a marine surveyor I have seen more plywood/polyester resin failures than I can count. The best ones are where you can just peel sheets of the glass of the plywood......saves grinding LOL
I only preglassed the bottom panels on my Volkscruiser because they were going to be to hard to glass once in posistion.

Happy sailing

Anyone in the industry has seen botched work in both polyester and epoxy.

Anyone in the industry has also seen properly executed polyester resin layup over wood, which most definitely cannot be peeled come hell or high water.

If you want a real treat, read Larry Pardey's discertation about the risks of using epoxy.

[Fore and Aft]

I did not realise Larry Pardry was such a guru on epoxies.......I have been using them here in Australia, Canada and New Zealand for 25 years and never had any rashes or reactions. Got two healthy kids as well so no latent effects yet.
Like all chemicals the correct Personal Protection Equipment when handling them EVERY time minimises the side effects.
Cheers

[Scout 30]

You might want to post this question on the WoodenBoat Forum. It's a specialized boat building forum. I can guarantee that you won't get any ridiculous recommendations to build with polyester resin there. Cold molded & stitch n' glue boats are always built with epoxy for a reason. When you get a boat kit from Chesapeake Light Craft they send you epoxy for a reason. Sam Devlin builds stich n' glue boats worth hundreds of thousands of dollars with epoxy for a reason. Call up Sam Devlin & ask him why he's not using polyester resin. I'm sure he could use a good laugh although what ramblinrod is proposing is not very funny. I've seen the disastrous results of taking the cheap route with polyester resin firsthand & it's not pretty. And good luck ever selling a wooden boat built with polyester resin. In fact, good luck giving it away.

[Terra Nova]

You glass AFTER you build it.