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.

[apex1]

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]

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/

[rwatson]

Sorry rw wrong (as usual),

Arrogance is cheap ! or are you just hungover when you go online?

what has foam in common with tortured ply? Exact! Nothing.

It is an excellent substiture, thats what! Perhaps you would like to look up the number of commercial builders in Plywood V Foam in the world. With thin foam, I can get curves that would snap any plywood, If I groove thicker foam, I get an equivalent shape with a lot less work.

There is very high quality ply at the market, at reasonable prices. Foam is not available at reasonable prices.

Yes, there is also a lot of real rubbish as the last 12 months of comments will tell you. I daresay you pay similar rates in EU, we are having $AU120 per sheet. The comparable panel in foam and glass is about 20% dearer, doesnt rot and is a way lot lighter.

And a epoxy layup will hold as good on ply as on foam (in some cases even better).

Did I say it wouldnt????

On foam ,you dont need to use expensive and unhealthy epoxy. Vinylester will save money and do a great job

[apex1]

Arrogance is cheap ! or are you just hungover when you go online?

May I send this back? (unused of course)


It is an excellent substiture, thats what! Perhaps you would like to look up the number of commercial builders in Plywood V Foam in the world.

Rw you should try to understand what "tortured ply" as a building method means! You would soon notice, that your statement is silly.



I build in both materials rw, believe me, epoxy is the better choice on ply. And foam, as mentioned above, has nothing to do with the building method! Tortured ply is what the name says "plywood", not steel, aluminium or foam and glass, no, just ply!
Tortured, of course......................................

Regards
Richard

[szkutnik]

wrong (as usual),
Regards
Richard
This is not fair!
It cost nothing to say sorry.

[gonzo]

I don't think foam would create the stresses to be tortured like plywood. It may bend more, but that defeats the purpose.

[apex1]

Marek
one says sorry when one feels sorry, or was wrong, I was´nt.
You cannot make a "tortured plywood" structure using steel or glass. But TP was the thread topic, not foam and glass, or anything else.
Richard

[szkutnik]

rw, believe me, epoxy is the better choice on ply.
Richard,you are wrong!You don't read carfully.
rwatson is right! He sed
-On foam ,you dont need to use expensive and unhealthy epoxy[/B]
Other words- Youhave to use epoxy on plywood.

But you Richard sed: epoxy is better choice on ply.
Many people will anderstand that vinylester or poliester are good on ply but epoxy is better.
In my and Rwatson opinion epoxy is only choice on ply.
In yours, just better choice.
IMHO you are wrong(should i sey -as usual-? No, i will not say that.
I just looked at two other threads and on both you was wrong.
I am afraid to read more.
But it doesn't mean that i can say :wrong ,as usual

[apex1]

But you Richard sed: epoxy is better choice on ply.


Yes I said so, and that was correct.

You do´nt get it Marek.

First point,
we do NOT discuss FOAM, STEEL, GLASS, PAPER, LEATHER and ONION SKIN here!

The thread topic is "TORTURED PLYWOOD" that is a proven boatbuilding method. I thought you would know that, being a boatbuilder?
So, one cannot substitute plywood by any other material, there is no such building method as tortured foam, thats nonsense.

Second,
of course one COULD use polyester or vinylester on plywood, and the industry has done it for 50 years now.
Again, as a boatbuilder you should have known that.

So, after rw was wrong (or at least completely besides topic), now you are going to make his mistakes too.
He is a amateur and has every right to be wrong.
You claim to be a boatbuilder, you have no right to be completely off the track!

Regards
Richard

and please let me know where I was wrong on other threads....

[ancient kayaker]

... and please let me know where I was wrong on other threads....

I hope they don't:) We need to get back to the original discussion, which was of interest to me at least.

Is there a measure for how much ply can be tortured, I wonder. It would have to factor in thickness, plank width, twist per unit length, and wood characteristics. Is it possible to quantify it? Free!Ship provides some data but I for one don't know how to interpret them.

[szkutnik]

You claim to be a boatbuilder, you have no right to be completely off the track!

Regards
Richard

and please let me know where I was wrong on other threads....
Sorry ,but as a professional boat builder, i will not use other staff like poliester in tortured ply metod ,what you suggest.
IMHO epoxy is ONLY ONE good choice on tortured ply.
Thats all i sed. Is it completely off the track!
?

where wrong?
You sed - mat is just weight but has not much strength.

If mat is just weight, why thousands boats are not falling apart into pieces.

Using a fabric you can choose the direction of load transfer and build a lighter boat but in places without directional load mat is as good as fabric.
In my work i don't use mat, but not because "mat is just weight but has not much strength".
There are other important for me reasons.

The rest is just asking you to stop offend people.

Regards
Marek

[apex1]

Thank you szkutnik, for the very deep insight in your level of knowledge!

Now can we please return to the topic?


Terry
I do´nt have any data, and never built in TP method. Also I can not find how the Freeship data would help.

Regards
Richard

[ancient kayaker]

In post #3 I mentioned "new design with bottom planks that will each have a 85 deg twist from midships to the stems" which I have as a FreeShip model. The image shows the hull using the "developability" mode. In the plank developments the "edge error" reported by FreeShip varies from 0.0044 (0.44%) in the case of the garboard, shown mostly in warning red, to zero in the case of the upper planks shown in green.

FreeShip seems to show one edge error value only, the other edge is always zero. If it assumes no strain along one edge then perhaps half the displayed FreeShip value might be taken as the edge strain, in which case 0.22% is the highest number any of my designs have.

I have data for white oak, tension yield point 4,760 (psi) and modulus of elasticity 1,780,000, which would make the yield strain 0.27%. For white pine yield strain is 0.29%. The data for Okoume is from a different source, I have less confidence in it but it indicates yield strain of 0.35%.

I haven't built the new design yet, but I modelled the garboards. It seemed to me that the okoume ply was within its limit, no noises and it sprang back most of the way to flat when released. From the above data it would be at 63% using half the FreeShip edge error value and 126% using the full value.

[apex1]

Let me play with it.

[gonzo]

The way I look at tortured plywood, it where there is bend in both ways and maybe some edge set. I suppose a program would have to include data for the thickness and type of plywood. I have build and helped with kayaks and canoes. However, building a small model doesn't work well for this method as for simple developed shapes.

[nordvindcrew]

Check out Paul Gartsides' flash boat. It is a tortured plywood rowing boat. Extreme curves in the ends

[gonzo]

They produce some really pleasant shapes.

[PAR]

Yes, there is a measure of how far plywood can be tortured. I have a list of radiuses I can expect different thicknesses and types of plywood can reliably bend to, before rolling sheer and interlaminate issues crop up. The there's the experience thing. I can usually over bend plywood, past my guide lines, using my ear to tell me when I've reached the maximum limits of the plywood's tolerance on this particular radius.

The list can be long, because it shows each size (1/4" on up) in long and cross grain orientations, also different species and veneer counts. For example a 3 veneer sheet of Douglas fir can bend further (tighter radius) then a 5 veneer sheet. The list includes Douglas fir, Okoume, Meranti and Saple. The "compound sheets" (faced plywood) should be judged by it's interior veneers.

Anyone interested in this list, email me and I'll send a copy. Of course, I'm not responsible for any cracked or broken plywood, bent to these radiuses, other then to say, I've successfully bent pieces to these dimensions previously enough to warrant including them on the list.

[ancient kayaker]

Let me play with it.

Richard: did you need the FreeShip file for that? It is attached if you need it. You will notice that the 2 sides of the hull are separated by about 3/8" so the plank developments allow for the keel and stems.

[apex1]

Richard: did you need the FreeShip file for that? s.

Of course Terry. thanks...

But will not do it before Monday or Tuesday Ok?

[dskira]

One good way to torture the ply wood, yes plywood not foam, is to take okume ply, and soak copiously with alcohol and quietly take pressure on the ply on a very good male jig, or in a female deck jig (like the Tornado, but this is another technique) and bring it to it's unatural shape. Fasten in order to segragate the bulges, and then come from outside each bulges to the center with the fastening.
You end up with a smooth shape.
I built a lot of little boat like that, it's fun, quick and it looks great.
Compound shape in larger boat can be done repeated the process until the scantling is met. The volatility of the alcohol allow the ply to be glued. The choice of sheathing is not important, everybody has is own soup.
In tortured ply, it is ply involve, the rest is cosmetic.
RWatson, you are not correct. Ply is ply, foam is foam. Richard is right on this one.
Cheers
Daniel

[rwatson]

RWatson, you are not correct. Ply is ply, foam is foam. Richard is right on this one.
Cheers
Daniel

Good grief man - are you still rabbiting on about my harmless comments.

For the sake of you rabid ranters the orginal post - yes the orginal post!!

quote " I thought the market would be inundated with designs for the new method"

So, in the spirit of good natured discussion, I comment on WHY the world is not "inundated" - and I get all this grief about straying off the subject.

We need a few people who think before putting their fingers in gear !!!

[dskira]

Good grief man - are you still rabbiting on about my harmless comments.

Yes :P
Just kidding
Cheers
Daniel

[fabrice]

Sorry to interfere, I'll just post my newbie and amateur question :
ply is now available "foldable".
One could use it instead of torturing standard ply, couldn't he ?
hum, foldable is not the accurate word : bentable maybe.
Like that : (sorry, french adress)

http://www.bois-et-parquets.com/produits-bois/panneaux,contreplaque,cp-cintrable,14.php

[ancient kayaker]

Fabrice: flexible plywood is available, it has special laminations and grain directions which make it very easy to bend in one axis, but still stiff in the other direction. It is used for round shapes in furniture and other applications. When 2 layers are glued together it becomes stiff like ordinary plywood.

Babelfish translation:

Fabrice : le contre-plaqué flexible est disponible, il a les stratifications et les directions de grain qui le rendent très facile à faire plié à un axe, mais toujours le stiff spéciaux dans l'autre direction. Il est employé pour des formes rondes dans les meubles et d'autres applications. Quand 2 morceaux sont collées ensemble il devient raide comme le contre-plaqué ordinaire.

[fabrice]

ha ! FLEXIBLE ply :rolleyes:
sorry about that !
not always that easy to translate technical datas !

Thanks anyway.
So, you just can't work it both axis at the same time, it's just like the average ply ? :(

[gonzo]

It bends easier in one axis. You could torture bend that plywood too.

[Steve W]

I dont think that bending plywood is exterior bonded so check that out before you get too excited.
Steve.

[fabrice]

I dont think that bending plywood is exterior bonded so check that out before you get too excited.
Steve.
hey, stop reading my mind, that was my next question ! :D

[ancient kayaker]

Flexible plywood will bend much more than regular plywood in one axis, it is rather stiffer in the other axis but not much. However the stiffer plies are thicker and will break before regular plywood would.

If I wanted a curve in both directions that regular plywood could not do, I would use strip plank construction, at least on the curved portion of the hull.

[outside the box]

Hi there all, just thought I would chip in with my two cents worth re Bendi or flexible plywood.
I am building a split moulded Catamaran to my own design here in New Zealand and am using "A" bonded flexi plywood for the core with internal stringers and glass on inner and outer just as one would with a foam core.
Attached are a couple of pictures to show the shape achieved also a picture of an Australian Tri built using same method, benefits are it is very fast to work and nice shape can be achieved.
regards to all Craig

[outside the box]

More photo's of Auz Tri build method.

[outside the box]

My own design that is shown in first post.
Regards
Craig

[outside the box]

Had wrong photo format.
Craig

[gonzo]

Nice design, but it doesn't look like tortured plywood

[outside the box]

No as mentioned it is flexi ply as that was being discussed when I chipped in, sorry will butt out now.
Craig

[Ilan Voyager]

There is a bit of confusion in this thread...I have some experience in compounded (or tortured I do not like this word) plywood as I have made 5 "18 feet" catamarans with this method. The last one was a 18 sq.meter mono rig weighting only 89 kg (196 pounds), with a width of 3.20 meters and a mast of 10 meters...

Wood has a very special way to answer to compression stresses; the cellulose cells will deform but not collapse and with some precautions won't break in tension. And it's this is the quality that's used in compounded plywood.

You'll obtain shapes of double bends without wrinkles as the excess material in the compression side will gently "shrink". After you stabilise the wood with epoxy (epoxy is not specially dangerous, vinylester is far more dangerous because of the solvent styrene).
Steam, hot water and isopropyl alcohol can help to convince the plywood to bend...

Foam is useless for that as it has not the "good" behaviour in compression and it's too weak in traction.

Compounded plywood is when you "form" the WHOLE boat from 2 panels (example the Tornado catamaran). That makes very good cats and tris, and a few monohulls.

There are limitations; thin high prismatic coefficient hulls, light displacement and a major drawback for some relying on the computer magics: none software to help you. With 6 or 6.5 mm max practical thickness you'll be limited to about 35 feet boats. But the shapes obtained are amazingly varied.

In fact the lone way of design is to make 1/12 models with birch aircraft plywood of 0.8, 1 and 1.2 mm corresponding to 3, 5 and 6 mm okoume plywood. And experience.

It's eyeball boat building with just a few drawings to guide you.

There are 2 main variations at my knowledge making a complete hull from 2 side panels:

Stressform of the Gougeon Bros (the 6 mm plywood is coated with epoxy with a 120 to 200 grams/ sq. meter glass cloth OUTSIDE) so you can get more bending without breaking the plywood in tension.

Cylinder mold which uses pre-formed panel of 6 to 9 mm to get rounder hulls. Hughes has designs until 60 feet for a motor trimaran, and 40 feet in cats. The pics shown in the post #44 are a variation of cylinder mold. Very nice pics and boat.

After you have a variation with a bottom (grossly the water underside) made of glass, strip plank or whatever, and 2 plywood topsides that are bent to shape into a female jig. The possible weak points are the joints between the bottom and the topsides.

All these are a very good method as multihulls imply a lot of surfaces. And you get it fair and smooth, with very litle sanding. A true life saver.

Happy new year.