Stitch and Glue Questions

[Peter]

I am building a rowing dingy using the stitch and glue technique. It is my own design and meant to be cheap, easy to build, and LIGHT WEIGHT.

LIGHT WEIGHT is paramount because I have to carry it up and down the beach to use it. Trust me. An extra two or three pounds seems insignificant when you are carrying the thing down to the water, but when it comes to carrying it back to the truck after a long row those few pounds really matter! Along those same lines the boat will only be in use for brief periods and will live out of the water at other times; probably in my back yard on saw horses when its not on the lumber rack of my pick-up truck. No inside storage; hence the cheap and easy to build parameters. This thing is going to live a tough, probably short, life! The hull must be water proof enough that the wood doesn’t soak up moisture while in use or when exposed to occasional rain or snow, but it does not have to resist water intrusion through osmosis from prolonged periods of sitting in the drink or from water sitting in the bilge.

Most stitch and glue boats specify a layer of fiberglass cloth over most of the exterior of the hull. They also spec a layer of fiberglass cloth on at least part of the inside of the hull, particularly the bilges. In this way it is like cored hull construction. The glass gives it strength and the plywood acts as the core. I can already tell that I do not need these cloth layers for panel stiffness or strength. Since it’s a dinghy the panels have small spans and loads will be light, so the “naked” plywood has sufficient strength on its own. Also I am not going offshore or doing surf rescue so a hull failure wouldn’t be life threatening. So I am intending to omit the two layers of cloth and avoid the added weight of the resin and fairing compound they would require. However I still need to fill the grain of the wood and to create an effective water barrier suitable per the aforementioned parameters of use.

Some Stitch and Glue boats use West Epoxy and roll it all over the hull even where there is no cloth as a sealant and water barrier. I suppose that would work but it seems excessively thick and heavy. Instead I am considering using some sort of epoxy coating inside and out, like a barrier coat or a thick epoxy primer or epoxy paint. Maybe even West thinned down with MEK or some other suitable solvent.

I have no experience with barrier coats or epoxy paints. Has anyone got any input as to what might do a nice job? Ideally it would be relatively thin so it flows and levels like a paint, but be just thick enough to fill the fine grain of the plywood and perhaps also fill the small holes left by the stitches (1/16 inch dia.) It would either leave a nice smooth finish, or could be easily sanded to one for a final color coat.

Any input would be much appreciated.

Thanks and Merry Christmas!

Peter

[CaptPatrick]

Peter,

Eat more Wheaties...

Plywood expands and contracts, even under dry conditions, enough to cause checking in any unreinforced surface finish. Once the checking starts, usually within a week, moisture intrusion is inevitable. Shrinkage of the resin as it cures further compounds the checking of unreinforced surface finishes.

Fiberglass cloth is absolutely necessary to keep the checking from occurring. You might be able to get by without reinforcement on the interior, but not the exterior. The interior of a hull is basically under compression, leaving the exterior under an expansion tension.

Epoxy can be thinned with denatured alcohol. It's not compatible with MEK...

Br,

Patrick

[CamB25]

Peter,

System Three makes a very low viscosity epoxy called Clear Coat. It works really well for sealing wood. A couple of coats will seal the wood and build up like 10+ coats of varnish. This product might be good choice for the interior surfaces. It has no UV inhibitors so you'll want to finish it off with a few coats of varnish or give it a coat of paint.

This is a picture of my Iroko coaming cap with three coats of the Clear Coat.

[Peter]

Eat more Wheaties...

LOL!

Plywood expands and contracts, even under dry conditions, enough to cause checking in any unreinforced surface finish.

Well I don't expect lots of moisture changes, but no way it isn't going to get the sh*t flexd out of it by trips up and down the beach not to mention what happens on he water. So I get it . Flexing cracks the finish and then water gets in. So put the glass on.

This is why I love this board. Experience and smarts!

Whle I was thinking and plinking I found this

http://www.storerboatplans.com/Faq/Salt ... tive2.html

Who knows what you find..... but this guy sounds like he's "been there done that."

Peter

[John F.]

Peter-

Chesapeake Light Craft puts together really nice kits. Take a look, it may save you alot of time and aggravation.

John

[Peter]

John;

CLC. I know them well. I actually have been using an instruction book from one of their kits as the main guide to my own bulid.

I have already got my hull completely together. Of course I learned a few things along the way...

Peter

[JohnD]

Peter,

Here's another source, I've got the plans for the v-12 and hope maybe 2012 is my year to build. Every time I start to think about getting the wood "life" gets in the way...

Anyway there's also a forum with techniques.

Plans use fg tape 6" wide on the seams and optional full fg on the bottom.

br,
JohnD