Stressed Ply Construction

[IanHowick]

Hi Michael, have you seen/played with this method of construction?



Building a stressed ply Development Rule International Canoe Hull

It looks adaptable to a quick canoe style of construction but with a bit of curve to the cross sections up front. More curved surfaces = more rigidity/ability to build from thinner ply without the oilcanning problem you're likely to have in the quick canoe with the wide flat bottom if you make it from less than 6mm ply. Could be an interesting way to go for the dedicated sailing version you're perhaps thinking of?

Ian

[PAR]

That's a mild form of tortured plywood construction. I've seen considerably more "torture" employed in the planking then shown on that link.

The basic problem with this type of planking is the panels are "pre-loaded" which detracts from their strain carrying capacity. In fact, during testing, it's been found that panel failure often takes very little additional strain, because of the amount of pre-load the torture places into them, during assembly.

The net result is a weaker panel system. To accommodate this tendency, less torture is used when developing panel sections, but then you lose much of the attributes so desired from the torturing process.

In short, if the boat is light and not very highly loaded, you have a fairly good chance of success. On the other hand if you max out the radiuses possible with the panels and load them up good, then just the slightest additional loading can cause catastrophic panel failure.

Of long term durability, it's been found that rolling shear in the panel veneers often causes failure. This is a reasonably common form of plywood failure, though usually seen in appendages rather then hull shells.

[Boatmik]

Howdy,

I have not used that type of method. I am computer based and computers cannot deal with high degrees of forced curves and certainly cannot work out required panel shapes when they are compounded much at all.

MIK

[robhosailor]

My friend Krzys Mnich designed many boats for tortured ply method. One of them is a small proa Wikiwiki:

Picasa Web Albums - Krzysztof.Tuz - Ogólnopolski ...

Picasa Web Albums - Krzysztof.Tuz - Ogólnopolski ...

and his (designed circa 10 years ago) first proa with paraglide wing Nietoperz (Bat):

Picasa Web Albums - Krzysztof.Tuz - Ogólnopolski ...

Picasa Web Albums - Krzysztof.Tuz - Ogólnopolski ...

And monohulls too:





And interesting article with pics about another his boat named "Aurora"

http://www.port21.pl/technika/article_1718.html



----
More photos of proas in Poland there:
Picasa Web Albums - Krzysztof.Tuz - Ogólnopolski ...

[PAR]

I've "played" with it Mik, at least enough to evaluate the minimum radiuses permissible for plywood, before you've "loaded it up" too much. In reality, it's a "shoot from the hip" approach, with guess work and speculation as major engineering tools. One good thing that has come about as a result of the tests and experiments is, I have a very reliable list of radius minimums, which is handy for more conventional planking methods. As far as getting EU or ABYC (or other scantling guide or compliance) you can pretty much forget about it, so this leaves canoes, kayaks and other small, light craft only as possible parents of this method.

[Clinton1]

That plan/build was made by a competitive International Canoe sailor, and sold to a competitive I/C sailor, and appears to be still sailing after quite a few years.

Due to the build time and introduction of exotic materials, I do not think it meets the 'quick' part of the Quick canoe 'concept'.... but at the moment I am very, very tempted by it and the maker has put me onto a local-ish person that has used the design; in order to see, first hand, what can be done with this design.
Mind you, I'm the person that spent 2 hours at the local bay, studying the young lass doing her kayak training runs, thinking of boyancy, sails and QC155 re-designs, and paying no attention to the the young lass.

I think the stressed ply concept appeals to me because I have not done it, as opposed to any other reason...

[robhosailor]

If you are interested in this method of construction of boats - there is a very interesting article with pics of concept designs of couple of boats from tortured ply and described principles of the techology (in Polish) - by the boat designer Krzys Mnich:

http://www.sail-ho.pl/article.php?sid=1591

For example:

[IanHowick]

Thanks everyone for the information and links, I was curious to see some of the pluses and minuses of this construction method and what else had been done along these lines.

Interesting to see the remarkably light IC10's and foiling Moths being built by Phil Stevenson from 2 and 3mm ply.

Ian

[robhosailor]

Interesting to see the remarkably light IC10's and foiling Moths being built by Phil Stevenson from 2 and 3mm ply.

Yes - tiny plywood and carbon fibre or kevlar or glass and epoxy laminate

[Boatmik]

Thanks everyone for the information and links, I was curious to see some of the pluses and minuses of this construction method and what else had been done along these lines.

Interesting to see the remarkably light IC10's and foiling Moths being built by Phil Stevenson from 2 and 3mm ply.

Ian

The standard for scow moths at the end of their development was 0.7mm ply with 1.2mm in the cockpit. An 11ft boat that weighed in at 32 lbs.

MIK

[Boatmik]

Yes - tiny plywood and carbon fibre or kevlar or glass and epoxy laminate

Howdy,

This way madness lies!

The thing that is being attempted with all lightweight structures is the lightest and thickest sandwich possible with the highest stiffness faces.

With timber you go to thin ply for the skins and closely spaced web frames with multiple stringers which are "up on edge". With the moths in the above post the stringers were 24mm x 9mm.

With composites the lightest core possible with the highest modulus fabric on the outside.

The most important aspect of both is effective thickness.which is the job of the stringers inthe timber construction and the job of the core for the full petro chemical composite.

The composite fabrics and the associated epoxy are really heavy compared to timber so allying them with a thin timber call uses all the weaknesses of both systems. The timber is not thick enough to make a contribution and the composites are not far away from the centre (neutral axis) of the laminate to make enough difference.

You can see of some of the forums around the net that some are experimenting with "lightweight" cedar strip and taking a silly approach. They think they are being clever though.

They think the timber is the least effective part so they reduce the strip thickness down to 4mm or less from the normal 6mm. This means they are removing the lightest part of the laminate and also losing the effectiveness of the glass or carbon. The stiffness of a cored composite goes with the square of the core thickness. So by reducing the core by 2/3 they are making the composite less stiff by 4/9.

They are reducing the stiffness by more than half without reducing weight much.

A better way is to go for lighter glass. They are generally using 4oz (130gsm) cloth - which is the standard for lightish canoes. But where is the 4oz really needed?

My balsa canoe was quite long lived but was 7mm balsa (keep the core thickness) and very light 0.7oz cloth with the cloth doubled over the areas of the bottom and interior that would lean against solid surface.

There was also a Proa built out of very thin ply with carbon skins inside and outside which failed by breaking apart a few years ago. They ended up with a hull weight I could have beaten well just by using 6mm gaboon ply.

I think the sooner we can instill the habit in people of sitting down and running a few rough calculations ... the better.

Most lightweight boatbuilding, except for that related to race boats is misapplied and misdirected. I've lost count of the carbon masts that are heavier than wood ones because people have started with inappropriately small diameter tube and build it up to strength with more carbon. Design for bending stiffness again. The best thing is to have a diameter big enough to reduce the need for materials on the outside of the tube.

Best wishes
MIK

[robhosailor]

This way madness lies!

Whenever: Krzys's "Aurora" is made from 4 mm plywood and coated by thin glass and poliester (epoxy is prohibited by class rules!!!) laminate - she's hull is really lighter than other GRP and sandwich boats's hulls in her class and she is really strong and stiff.







Sails provisionaly used from other boats!

[Boatmik]

I've "played" with it Mik, at least enough to evaluate the minimum radiuses permissible for plywood, before you've "loaded it up" too much. In reality, it's a "shoot from the hip" approach, with guess work and speculation as major engineering tools. One good thing that has come about as a result of the tests and experiments is, I have a very reliable list of radius minimums, which is handy for more conventional planking methods. As far as getting EU or ABYC (or other scantling guide or compliance) you can pretty much forget about it, so this leaves canoes, kayaks and other small, light craft only as possible parents of this method.

Exactly.

My chosen methodology doesn't allow it either.

MIK

[PAR]

It's interesting to note that, although there's always a constant suggestion that "lighter than other GRP and sandwich boats", yet there never seems to be any data, nor major design contributors (well established NA's for example), let alone substantive testing or correlation. I've done some, but enough to not really take it seriously. A friend of mine, whom also is the patent holder on constant camber panel construction methods (another odd, but valid building method), laughed when I brought it up, in a phone call the other day. Now, I do have to qualify this with the fact that Daniel is a bit conservative in regard to new techniques.

[robhosailor]

It's interesting to note that, although there's always a constant suggestion that "lighter than other GRP and sandwich boats", yet there never seems to be any data, nor major design contributors (well established NA's for example), let alone substantive testing or correlation. I've done some, but enough to not really take it seriously. A friend of mine, whom also is the patent holder on constant camber panel construction methods (another odd, but valid building method), laughed when I brought it up, in a phone call the other day. Now, I do have to qualify this with the fact that Daniel is a bit conservative in regard to new techniques.

Hi PAR,

I wrote:

she's hull is really lighter than other GRP and sandwich boats's hulls in her class and she is really strong and stiff.

We know data of boats of our national class Zagle500 ("Aurora" designed according to class rules, but built after newest changes of rules) - they are constructed form poliester/glass laminate and with poliurethane foam sandwich (decks etc.) usually and their weight of hull is known for public. Carbon, kevlar, epoxy prohibited are.
For reason of really lighter wooden construction (tortured plywood especially) newest rules of this class prohibited them.

Tortured plywood methode was choosen by Krzys especially for amateur construction, similar like this one (traditional plywood):

Sztrandusia - Zagle 500

Newest rules of this class prefer professionally by yards built boats - expensive and with haevier hulls.