Skin on Frame

 

 

I keep going back and forth between a stitch and glue and skin on frame for my next build. I like the wood hull of a stitch and glue but the ease of a Dacron painted hull over resin and fiberglass cloth

 

So what I was wondering can a stitch and glue be covered with heat shrunk Dacron and paint in place of fiberglass and epoxy resin?


9 replies:

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RE: Skin on Frame

You'll want to waterproof the wood somehow in case the Dacron tears. You'll also want to make sure that the hull is smooth so you won't snag the Dacron. Then you'll be applying the Dacron. It seems to me that by the time you do that, you're exceeding the labor that simply painting the hull would be.

Which part of finishing resin and glass is the problem?

If you're going to paint it, you can fill the weave with fairing compound, no need to fill and sand with epoxy. A microphenolic balloon/epoxy mix is easy to mix, easy to apply, much easier than epoxy to sand and will give you a nice surface to prime and paint. I find filling the weave that way much easier than filling the weave for a varnish finish.

But if you really want to go with the Dacron over wood, I think all you need is a glue that's compatible with whatever waterproofing coat you put on the wood. I think that the main issue will be that the wood and Dacron have different coefficients of thermal expansion, so as the temperature fluctuates, they'll separate and rejoin. This may result in material fatigue and tears.

Good luck,

Laszlo

 

RE: Skin on Frame

 

   How is this really different from a canvas covered canoe many of which are being restored by covering in Dacron?

I was more concerned with whether Dacron would provide the necessary strength?

I guess I am thinking heat shrinking and painting with oil based latex versus mixing epoxy and all that comes with it epoxy and glass are not exactly friendly materials versus heat shrunk cloth

 

RE: Skin on Frame

   To put it another way you really can’t get the mix ratio wrong on cloth or have it fail to set or set too fast

RE: Skin on Frame

I guess it isn't, really, except for the fact that the original canoes were designed to be covered with a softer textile that is bonded using a weaker glue . I guess it all depends on how you use the boat.

My thought is that for tensile strength, Dacron may actually be better than glass and it's abrasion resistance you need to worry about. There, epoxy/glass wins hands-down. It's as hard as Formica.

As far as the ease, I guess it's all what one is used to. I find the idea of heatshrinking Dacron a lot more worrisome than getting a good epoxy/glass lay-up.

So try it and tell us what happens. It'll be an interesting story.

Have fun,

Laszlo

 

RE: Skin on Frame

   “I guess it isn't, really, except for the fact that the original canoes were designed to be covered with a softer textile that is bonded using a weaker glue . I guess it all depends on how you use the boat.”

Exactly my thought it isn’t designed for it so I was worried does the wood need the glass for support

RE: Skin on Frame

We may be talkin' about three different sorts of boats here.

First, there're skin-on-frame boats. Think Inuit kayaks and umiaks, and modern derivitives like Folboats and designs by Platt Monfort, Dave Gentry, etc.  In these, the "skin" (leather, canvas, etc.) is stretched over a frame without any real planking to support the skin between the frames and stringers.  I suppose the Inuit developed this from a need for light boats in an environment lacking much in the way of suitable wood for planking.  Produces a light, strong boat, but mind the sharp rocks.

Then, there are canvas-covered boats.  Think old-fashioned wood-and-canvas canoes where closely-spaced, wide frames support thin planking which is then covered by canvas stretched over the planking, bedded in white lead, paint, etc.  Not just canoes, really.  The example of William Atkins' design for the Penn-Yan dinghy comes to mind.  (See at http://www.atkinboatplans.com/Dinks/HandyAndy.html and have a look at the photos.)  The planking isn't closely fitted (not lapped as in old-time cedar canoes like Ruston's), isn't thick enough to be caulked as in a carvel-built boat, and isn't edge-clued as in a strip-built boat, but it supports the "skin" more evenly than in a skin-on-frame boat while still making a pretty light boat.

Then we've got these marvelous "stitch and glue" plywood boats, which are a whole 'nother thing.  The structure, if properly glued up, is inherently watertight.  Epoxy on the surfaces is to strengthen the plywood and help keep the water from getting in between the plys better'n paint alone would.  Any fiberglass (or other material- dynel, kevlar, etc.) applied would be for strength or abrasion resistance or both.  Plywood, epoxy, and glass cloth are well-suited to this type of construction.

That's something of an over-simplification, but maybe that helps?

.....Michael

RE: Skin on Frame

   I have biult and used both 'Skin on Frame' and 'Sitch and Glue' solo canoes and kayaks     (one of each). The are both around the same amount of work, but completely different processes.  Both are great, but untill you have biult and used one type, don't mix the process - both are very well worked out and produce great boats. 

Joel

RE: Skin on Frame

I'm with Gramps- and I'll venture a further simplification:

No, you can't. :)

Yes, in both cases we're talking about fabric saturated with some sort of goop- but the qualities that are/aren't important to each SYSTEM are so different that the best materials for each will not be interchangeable.

With S&G, the glass/epoxy is crucial for strength and structural integrity. You want the fabric to bond with the (rather fragile) wood core, inside and out- creating a rigid shell. 

With SOF, the fabric simply needs to be strong enough to resist whatever tears you're worried about, and the paint/varnish just needs to keep the water out while remaining flexible- it's not terribly important for the cloth to bond to the frame.

With my SOF, I can put my 200# self atop the unskinned frame and BOUNCE. The frame flexes- by design- but does not break. Don't try that with an unglassed S&G craft. While the fabric and sealer I used are very durable, it is- by design- still very flexible.

Good luck,

Patrick

 

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