Compounded (tortured) ply construction.

Hi,
I think this is my 1st posting. There is a lot of inaccurate info published on tortured ply construction, usually used for kayaks & multihulls - Tornado cat being original example.
However, I believe I came up with this method of boat construction in the mid-1960s when I was teaching woodwork in an English secondary school. In the exam classes (14-16s) there were some lads (no lasses in those days) who while quite happy to do their woodwork, were not interested in having to make things for which they had to pay. So with the co-operation of the Head/SchoolFund I came up with the compounded ply method of building kayaks which could be hung from the ceiling in between building sessions - once per week. From hazy memory the idea that it might work came from looking at a half grapefruit peel cut into three. See my book, pub 1969 'The Book of Canoeing' Dennis Davis or take a look at <dennisdavisdesign.weebly.com> for how it has developed. Dennis.

 

Dennis,
your link doesn't work (design ... designs).

 

No problem, the link is working perfect for me.
http://dennisdavisdesigns.weebly.com/ . Bei mir geht das gut. Auch der Zugang zu facebook ist perfekt: https://www.facebook.com/dddesignsboatplans . So ist das Internet, mal geht es und mal nicht - launisch wie ....

 

Manfred, your link works, because you were adding the "s" which is missed in the thread openers (first) post. (Ich hatte die Seite ja nach Suche dann auch gefunden.)

 

If you're claiming that you thought of this first, it would help if you could remember the year more precisely. According to the book The Gougeon Brothers on Boat Construction, they built a tortured-ply trimaran in 1963. However, they give the credit for the general idea to the American Indians for their birch-bark canoes, built about 200 years earlier.

This is not to belittle your possible accomplishment, though. There have been many examples throughout history of the independent discovery of great ideas.

 

I'm sure that several persons had the idea when handling thin plywoods during the 50 and sixties. The interesting fact with thin plywood is that the inside face in compression will "crunch" before putting the outside face in too much stress by tension. The limit is the strength of the interface outer ply and central ply. Steam can help a lot.
Like the Gougeon you can go farther with the Stressform method by improving the tension performance of the outside face with a coat of epoxy glass and getting more crunching of the inner face. The cellulose cells literally implode and are stabilized later with epoxy and glass. That works best with a 3 or 4 mm 3 plies. But some 6mm 5 plies give excellent results. You can get shapes pretty far from the original developpable plane.

The birch canoe has surely less than 13000 years but surely more than 1000 years. After 1620 there has been a "race" to make then bigger and bigger until 1820. True cargos at the end.
I'm almost sure that Uffa Fox made compounded plywood dinghies in the 1950 at same time that the cold molded, and chine plywood ones.
Some Caneton 14 feet dinghies were made in compounded around 1955-57, maybe before. Mr Eugene Cornu made one or two around 1958 if I remember well after his Caneton 57, when he was trying to improve this last design.
Some Canoe International were in compound but I'm not sure of the dates 50 or 60. The Moth ancient style also.
After WWII everybody played with plywood and veneers, hot molded (using the WWII tooling of the Mosquitos) generally urea-formol glued, and after cold molded with resorcinol, and some made or tried to make compounded boats in a lot of variations at least during the 50.
The Tornado 1968 did not appeared from nihil, several cats were made in compounded at least during the sixties as the Manta by Mazotti in 1964 and the Unicorn in 1966, themselves inspired by the compounded dinghies of the fifties. It's highly probable that the method was tried on cats at the end of the fifties or very beginning of the 60. Several were tinkering with compounded in the States, and the Gougeon made their C class tri in 63. I have the remembering of one monohull in Germany around 1970. The problem was the glue; many tried with polyester "glues" and these boats were very short lived. That was solved by the epoxy and all its methodology.

With the advent of the epoxies (invented around 1940) in the 1950ties, appeared the epoxy wood. I saw in 1974 at Malmoe 2 epoxy-wood skerries made around 1955 with an epoxy looking very much like araldite at least by the peculiar smell.
I have been told by my apprenticeship master in 1970 of a precursor at the end of the 40 maybe in England.
That I'm almost sure is that around 1955-58 several builders made wooden boats glued with epoxy in the States, UK and Sweden. My master was building wood-epoxy at the end of the 60, and myself have been initiated on this method in 1970. The resins were pretty dangerous, with some spectacular cases of sensitizing, rashes and eczemas. But we had already the low viscosities reactive diluted resins made in Sweden by a formulator. The first epoxies were as thick as tar. The present epoxies, no blush, no carbamate, no fish eye, low viscosity, hardening in a wide range of temperatures and tolerant to the ratio hardener resin are a pleasure compared with the delicate 1970-1980 resins.
The Gougeon have the credit of improving the epoxy-wood to an adult and reliable boatbuilding method open to the DIY, and made a lot with their manuals and books.

 

Thanks for the comments.
No, I was not claiming to be the first, I am sure that others were, or had been, experimenting similarly prior to me. I was certainly the first in the UK to produce a useable kayak design utilising the compounded ply method. An article I wrote & published by Woooden Boat on building the DK13 kayak - my first practical design - led to the development of at least one commercial venture which blatantly copied my design & photographs. I believe did Gougon brothers did mention my designs in one of their publications, although not so far as know in the only book of theirs I own, very good incidentally. Best wishes, Dennis.

 

Many thanks Dennis for the precision, in fact a lot of persons were tinkering with the concept of compounded plywood for different boats, but very few arrived to a usable design. Unhappily a lot of guys do not hesitate to copy with no shame, and it's almost impossible to sue them. The DK8 is a treat for a young adventurer, that would make a nice father/child project. The DK21 and DD 17 are very nice sea kayaks.

 

A former member here Daniel Skira has a patent on this process, dating in the 60's, if memory serves me.

 

My own experiment in tortured ply.

http://www.boatdesign.net/forums/wooden-boat-building-restoration/15-lapstrake-kayak-40486-2.html

I think the guts of it are in posts 15-26.

 

compounded ply construction was used on wood aircraft prior to WW2, it took some time to adapt it to boat construction because I suspect traditional wood boat construction was still popular into the fifties and beyond.

The early Moony aircraft used plywood wings, later switching to aluminum skin. There were some german fighter designs using plywood in WW2 as well as the British Mosquito. There are no production wood aircraft made any more, all are done by hobby home builders today.

I have seen cold molded hulls on small boats that date from 50's, which is a form of hand laid plywood. It would be a natural progression to use it in lightweight boat construction.

Trying to identify who did it first would be difficult, if not impossible, considering the idea has been around in other industries for well before the 1960s.

 

Two fundamentally different methods to create laminated wood / plywood with compound curvature.

The first method is to laminate the veneers using a mold with the compound curvature, and it has two variations. The older version of this used adhesives which required heat to cure, and was used for boats into the early '60s. It was also used for some aircraft such as the WWII Mosquito. The newer version uses cold setting adhesives, usually epoxy, and is usually referred to as "cold molding".

The second method is to force a flat sheet of plywood into a shape which has compound curvature, and is referred to as "tortured plywood" or "compound plywood" construction. The possible shapes are limited compared to the first method. This is what Dennis is talking about. Chapter 25 of The Gougeon Brothers on Boat Construction describes this method.

 

Not forgetting that true waterproof glues were only available from around the end of WW2. Some 14's and Int Canoes were an odd laminate double diag with waterproof silk (and adhesive?) in between, at least in some constructions in the 30s'.

There are/were several ways of moulding, one using vacuum to pull onto a mould, another pushes a bag down onto the former, and a two part solid mould, maybe others including battening/stapling etc. I was using urea based adhesives into the 80s' for precision 'cold moulding' of racing sculls. However the adhesive was gently 'cooked' at relatively low temperature(s) to get the work ready to continue next day. Generally we'd glue up a layer last thing and leave overnight. Still to this day a reasonable way to make custom shaped ply, of fair shape, if a little time consuming.
The furniture boys had a lot of heavy duty press two part tools which could achieve a number of layers and some small degree of compound curvature for seats and the like.

We also had ways of getting 'impossible' curvature into veneers, and this did not compromise the laminate.

Compound ply/tortured ply can use the same tricks to a large degree, you just have to think round the problem. Also depends if you want a clear finish!
Generally I personally have given up forcing ply too much, the stress seems to manifest itself somewhere, and prefer to make up custom ply from veneer if needed. So I've ended up doing some local scarfing onto bent ply especially in the bow area(s). Same with curved thwarts, just laminated thin solid say 5-6mm a strip.

 

I note that the tortured ply deck of your kayak limits you to a size nine shoe. More a limitation of the stressed plywood method than a benefit.

 

Plywood was also used in hot molding, the forerunner to cold molding, which came about with room temperature cure adhesives. I own a Fairey Marine hot molded hull from 1957.