Tortured plywood designs

[gonzo]

When I first heard about tortured plywood it seemed like a great idea. I thought the market would be inundated with designs for the new method. A couple of decades later, apart from a few kayaks, there is almost nothing. I believe someone builds a minitransat with some side panels using this method.

[PAR]

Okay . . .

[ancient kayaker]

Depends what you mean by tortured ply, I suppose. My canoes have some twist in the garboards, quite a lot on one of them, and I have done some experiments on a new design with bottom planks that will each have a 85 deg twist from midships to the stems. I want to adapt it to a sailboat design later, if successful.

This is not a rolling bend or conical development, which doesn't "torture" the ply, not much at least. It is pushing the ply close to its limit. I doubt that I am the only one. But it puts a lot of stress into the ply.

By tortured ply I mean a shape that introduces significant tensile and/or compressive stress within the plane of the ply, not just on opposite sides. What do you mean by "tortured ply" ... ?

[gonzo]

It is bending plywood both ways. It will compress and strech the wood to a certain extent. I remember there was a craze and may designs were coming out in the 80's. The Gougeon brothers were making hulls with 1/4" plywood and then heavily glassing both sides.

[rwatson]

With the low quality, high price of ply - it probably is just too hard.

If you need something to hold wet fibreglass off the floor while it dries, marine foam does a better job easier.

[Steve W]

Tortured ply is only suitable for long skinny hulls such as multihulls and kayaks etc,Malcolm Tennant had a very nice cat design called Red Shift available and also a coupleof designs dating back to the late 60s i think,also hard to argue with the success of Meade Gougeons 2400lb 35ft 40yr old tri Adagio, rates something like negative 60s under PHRF on lake huron.
Steve.

[ancient kayaker]

Steve: I believe the stresses in the ply for a given angle of twist would be proportional to the square of the plank's width/length ratio. While you are correct in principle, dividing the hull into a greater number of planks would reduce the stress. That will soon become impractical, however.

Originally Posted by rwatson

With the low quality, high price of ply - it probably is just too hard.
If you need something to hold wet fibreglass off the floor while it dries, marine foam does a better job easier.

Sorry rw wrong (as usual),
what has foam in common with tortured ply? Exact! Nothing.

There is very high quality ply at the market, at reasonable prices. Foam is not available at reasonable prices.
And a epoxy layup will hold as good on ply as on foam (in some cases even better).

Regards
Richard

[szkutnik]

Sometimes this method works.Catamaran on the picture was built using this method in 1992. Hulls come to being very quickly and are lightweight.

[gonzo]

The "Constant Camber" method had a simple method for making panels.

[ancient kayaker]

The Carene software is very quick for creating cosntant camber designs. Constant camber designs make it easy to predict plank developments. I have been experimenting with cutting the seam bevels before bending the planks, since they are also constant. That was not as easy as I thought it would be, though. Still looking for the perfect design and build method. I like the idea of using foam for bulkheads, although I don't think that's what RW was referring to. I use insulating foam as a table top, makes cutting ply with a power panel saw a snap, and I assemble small boats on the foam as well. Even if glue sticks to the foam it just pulls off a fragment.

[gonzo]

I was thinking about modifying the constant camber to change it in the ends of the hull. Maybe just the last panels could have a different camber.

[ancient kayaker]

Originally Posted by gonzo

I was thinking about modifying the constant camber to change it in the ends of the hull. Maybe just the last panels could have a different camber.

Gonzo: if you are using Carene it will let you do that, at the ends only. What design are you working on, any pictures?

[gonzo]

Only in my head. I haven't used Carene. Can you give me more information on it?

[ancient kayaker]

It is no longer available from the original source. Try this one -

http://pagesperso-orange.fr/robert.laine/