glassing plywood prior to hull installation

[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?

[UNCIVILIZED]

Start here How Tough are They? | Epoxyworks

[Liburnian]

Several layers of 1cm ply would be quite rigid and difficult to bend, even if it would be high quality okoume ply. But it depends on area - bigger pieces could be easily bent and temporary screwed, as you've mentioned. You can even force it with straps to bend.
I'm building a 28' boat and usually glassing ply construction at the end, but bulkheads being glassed and later taped into the hull. The curvature could be also achieved when laminating the ply with battens or mold under and straps or some weight above. When epoxy cures it is easy to glass the piece.
My building method is according the bateau.com (How to build or repair a boat | We make boat building easy | Bateau2.com), similar to Devlin. Or check Gougeons' book.
Hope it helps.

[scott2640]

good stuff! I got problems, I love data!

[meatservo]

Funny! I spent the "wonder years" in Rochester...

Hope you have a warm place inside to work!




meatservo

[ggray]

It all depends on how much you need to bend them later. You might do a test panel and try it out.

I built this boat kit that has you pre-glass the inner side of the panels (except maybe 4 feet back from the stem):

PT Skiff

The idea being that the inside is a lot easier to fiberglass flat on a table than later when all frames are in place.

The panels do get stiffer, but not rigid. If you pre-glassed both sides, that would probably be a lot stiffer.

[Fore and Aft]

I pre-glassed the bottom panels on my plywood yacht before installing them in place. If you go to my website fore and aft surveyors and click on the Volkscruiser link you will see a picture of me bending a pre glassed panel. The flex is amazing.
Good Luck

[scott2640]

Originally Posted by meatservo

Funny! I spent the "wonder years" in Rochester...

Hope you have a warm place inside to work!




meatservo

Haha, lots from Rochester, it's getting them to stay that is rare. My shop is warm but the boat shed is mighty cold, especially with the winter storm advisory in affect.

[meatservo]

Checked out your website, might have to make a donation! hell of a project just building the shed.

Start a go fund me and then take Wounded Warriors sailing...



meatservo

[ramblinrod]

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?

Whoa, that's crazy talk.

The reason a core (sometimes plywood) is used in FRP laminate construction is to increase stiffness (with less weight than solid glass).

Making the wood stiffer by applying FRP over the surfaces before bending is therefore, a very bad idea. (Including that the bond between FRP and wood will be stressed during flexing.)

A better method is to bend the panel (steam if necessary), clamp it in place and let it set and completely dry out. Take it off, glass the inside surface, apply resin to any mounted contact points, and screw it in place, then apply the outside glass.

This assures that the entire inside of the hull is as water impenetrable as can be made, and the final composite is as strong as can be.

I recommend using Isopthalic (higher quality) polyester resin (unwaxed), as one can lay this up over many days or even weeks, and still get a good cross-linked molecular bond.

Despite popular belief and all the marketing bestowed on DIYers by epoxy manufacturers, results are actually superior using polyester resin (and it is way less expensive).

I thin the polyester resin with styrene for the first plywood wet-out coat so it really soaks into the wood fibres.

By using polyester resin instead of epoxy, then gelcoat can be used for the (light coloured) final finish above the waterline, which is applied with much greater dry film thickness, is much more durable, and much more easily repaired, than any sort of paint, especially including 2-pack like Awlgrip.

Below the waterline, I use a couple coats of Epiglass epoxy (at least .010" DFT over the polyester exterior, four coats of Interprotect E-2000 (alternating colours to assure 100% coverage), and the final anti-fouling, chosen by region and intended use.

Additionally, polyester resin is a lot safer (pools are less likely to catch fire while curing) and is less likely to cause dermatitis (in my experience).

In addition, polyester resin is much easier to adjust to suit the temperature conditions by simply adjusting the catalyst ratio, and is much less temperature sensitive, being workable from 5 to 35C, whereas epoxy is more difficult to manage outside of 15 to 25 C (requiring alternate hardener formulations).

[Scout 30]

For anyone that believes polyester resin sticks to wood better than epoxy please contact me. I have some beautiful swamp land in Florida to sell you.

[JOHNMARDALL]

Whatever you do and however you do it, remember that if epoxy is cured, you must wash off the amine blush (water will do it) before attempting to glue it or laminate over it. If you don't, the bond will fail, even if it takes a year or two to become noticeable. Learned it the hard way.

Good luck
John Mardall
Vetus Maxwell Group

[ramblinrod]

Originally Posted by Scout 30

For anyone that believes polyester resin sticks to wood better than epoxy please contact me. I have some beautiful swamp land in Florida to sell you.

Polyester resin sticks to properly prepared wood just fine.

Almost every production fibreglass boat ever built has polyester resin tabbed wood bulkheads.

Properly applied polyester resin bond is stronger than the wood itself and will rip off the wood fibres rather than peel off the polyester. One can't get any stronger bond than that. Adhesive properties stronger than the materials bonded is of little to no value.

[Squanderbucks]

I think you will be in a world of hurt if you try glossing individual sheets and try and use them. Unless you glass both sides of each sheet and at the same thickness and catalyst ratio you will produce cupped boards that are not really useable.
Try just painting one side of one of those sheets a see what happens. Besides you will loose one of the main benefits of glazing a boat after construction by giving up the one piece shell that binds everything into one unit. Epoxy is strongest. But you must weigh costs ease of fabrication in deciding between polyester vinylester or epoxy.

[Squanderbucks]

In addition you will be making a tremendous more amount of work for yourself because each board will be of a different thickness and the there will be tapped seams of additional thickness all of which will have to be faired and sanded much more.
Some of the epoxy manufacturers have brouchers and YouTube videos demonstrating glass application. If you build the hull upside down the woodwork and fiberglassing will be easier and eliminate the back breaking work of working overhead.