cold molded hulls

[Jonathan Chouinard]

Hi everyone, I have been thinking about starting my tiki for the past year now, but I'm not quite to the point where I have a suitable building space.  During this transition, I've had ample time to contemplate the building method that these Tiki's take to build. 

     In thinking about this build, it has occurred to me that this boat appears to contradict Mr. Wharram's whole philosophy, specifically being one with nature and such.  Occume marine plywood is made from a tropical hardwood that isn't particularly sustainably harvested, and isn't known for its rot resistance.  Epoxy is very toxic and is well documented for causing welts and allergic reactions.

     This train of thought has led me to contemplating other methods of building these hulls.  Has anybody successfully produced a hull using the cold molding technique?  I was thinking that by starting with thin strips of cedar, followed by veneer of something, then foam or corecell type material,  followed by a thin layer of fiberglass, kevlar, carbon etc it would produce a very lightweight but strong hull.  My main concern is that Wharram's plans aren't good enough to do an accurate job of making station molds.  Has anyone made a CAD drawing of a tiki design?  

    I'm hoping somebody can shed some light on the subject.  My inspiration for this line of reasoning is the Susan schooner thread on the woodenboat.com forum.  The guy built a beautiful yacht from locally grown timber, Lowes lumber, etc.  I like the idea of using local stuff, a little bit at a time, and not shipping plywood from africa, asia, south america etc.    

[boatsmith]

You can certainly build a Wharram hull cold molded. You will require even more  epoxy. The build will also take more time. Sheet plywood is a very fast way to build a one-off hull. If you don't want to use okoume plywood you can use US/Canada fir ply. This ply comes from planted trees for the most  part.

The Susan project is an entirely different flavor of vessel. You wouldn't do that build in sheet plywood

Just my thoughts, others will have different opinions.

[Jonathan Chouinard]

I was thinking that with with a cold molded hull, you could use other glues like regular carpenters glue or recorcinol (when vaccuum bagging the veneer).  Thanks for the tip on fir ply, I'll have to look into it.

[Axel]

Perhaps console yourself with the fact that Wharram does not specify Okume and like you makes the point explicitly that sustainably grown plywood is the preferred choice. Some builders choose to use Okume but it is not specified by Wharram.

 

I fear that if you are going to try to build a boat using any of the mentioned 'modern' materials you are going to be using significant quantities of toxic chemicals and supporting a system of production that is not geared to sustainability. But remember that epoxy is actually quite benign compared to many other resins and glues, especially the polyurethanes. And foam and glass are hardly likely to be more eco-friendly than ply, no matter where it comes from.

 

But anyway  if you are planning to use the boat as the designer did intend, you're resource footprint will be tiny in comparison with your western peers. Console yourself also with the fact that many Tiki 38's have been built to plans without too much  difficulty in achieving a smooth, hull. It does actually work to build it the way Wharram laid it out.

 

Perhaps the best thing to do is to get yourself to the rainforest in an eco-friendly way such as kayaking, cycling or walking, in  a handmade, wooden boat or on a fully recyclable bicycle. Live and work with a tribe for a few years, all without spreading the western model of resource exploitation, to earn the right to cut down a pair of large, hardwood trees. Then make yourself a giant dugout catamaran by hand. Anything less will surely be responsible for a continents worth of 'negative waves', man.

[alex]

frankly speaking i would use vaccuum bagged tech like the one from derek kellsal . i was investigating this before and sound very logical for me. i have lots of info to share. but i think its not the right place here, as its a wharram site. feel free to contact me at [e-mail] or at my YM add: vongraevenitz

[Jonathan Chouinard]

I think that both the process and the product are important.  Wharram's newest designs are over 20 years old by now, and there have been vast improvements in materials and processes.  I like the look of wharram's designs, which is why I am interested in building one of his boats, but I'm just contemplating on efficiency in building.  Of course ply and epoxy works fine, but I'm sure there are materials out there that are lighter, stronger and quicker to build with.  I'm curious what those materials are.  I would think that building in fiberglass/foam sandwich would make for a strong, light build.  It would be interesting to see some data on this.

Chuck Valley said:

Is it the process or the product that's important?

 

Chuck

[Geminidawn]

Cold Moulding was developed during the war an used to fabricate the fuselage on some planes. It's just a system of laminating plywood over a mould to develop curved surfaces but to develop those surfaces you really need the support without it your boat (or plane) would develop the "starved cow" effect, sagging between the ribs and bulk heads, not pretty.

The glue that was traditionally used was resorcinol and this is not exactly user friendly either as the fumes can burn. Neither dose resorcinol tolerate any errors, gaps of 1mm+ would fail.

Double Diagonal method could be used but this is also a bit outdated and a real pain to repair if damaged.

The only alternative method I would consider for a Wharram would be cedar strip. The result would be light, strong and a thing of beauty but it would take you forever and a day!

[Jonathan Chouinard]

wow excellent response, thank you.  I didn't realize that cold molding needed so much bracing, I thought that was a benefit of it.  I would love to build my boat in cedar strip, but like you said it would probably take forever to finish it!

[Damon Urban]

I've thought about vac bagging the hulls on the Tahiti Wayfarer. Specifically- building the hull from layers of thinner ply and vac bagging to avoid butt joint cleats etc. Two issues came up for me:

1. The panels would be much stiffer and potentially difficult to torture into shape.

2. Would the added strength be worth the added labor/pain in the ass  factor of dealing with vac bagging? I'm guessing probably not, these boats seem plenty strong.

I did notice a hyper text on the Wharram website called Vacuum bagging but it didn't lead anywhere. I'm still intrigued by the concept . 

[Geminidawn]

Usually I never use vacuum bagging unless I'm working with multiple layres of Biaxial or Quadraxial, Glass, Carbon or Kevlar.

Ply veneers are less pliable and have sharp edges that can easily rupture your vacuum bag and cause great loss of time and materials. On one such incident I've seen was a students end of year project get totally destroyed because of a poor ply/vaccum bag set-up and as a result had nothing left to submit.

If I am requested to produce complicated ply shapes I develop them well oversized and tape the edges to protect the membrane. Vacuum bagging with ply takes twice the ammount of set-up time than other materials and as stated is a real pain in the ass!

[Damon Urban]

I hear you. I've read about some interesting applications of vacuum for boatbuilding like cylinder molding and constant camber, but their's no getting away the added complexity and hassle factor using vacuum introduces. To take a boat thats been designed for stitch and glue and try to adapt it to vac bagging seems inefficient.  I think you'd basically end up designing another similar boat.  If one were to go through the trouble though,(getting very hypothetical) what do you think the potential gains could be in terms of strength to weight ratio?

Geminidawn said:

Usually I never use vacuum bagging unless I'm working with multiple layres of Biaxial or Quadraxial, Glass, Carbon or Kevlar.

Ply veneers are less pliable and have sharp edges that can easily rupture your vacuum bag and cause great loss of time and materials. On one such incident I've seen was a students end of year project get totally destroyed because of a poor ply/vaccum bag set-up and as a result had nothing left to submit.

If I am requested to produce complicated ply shapes I develop them well oversized and tape the edges to protect the membrane. Vacuum bagging with ply takes twice the ammount of set-up time than other materials and as stated is a real pain in the ass!

[Geminidawn]

On a Wharram it would be next to nothing, same weight minus a few buttstraps. If it were another hull with something like a cylinder hull or a constant camber and I was going to put in all the effort of vaccum bagging I'd be looking at a higher strenght to weight ratio like carbon to make it worth my while.

[robin craig jones]

Hi Jonathan

 

I am also looking into building a Wharram or similar traditional voyaging catamaran using the cold molding technique and bamboo double diagonal strip planking with a lattitudinal planking over the double diagonal. There are industrial PVA glues available that would build a very strong hull whos tripple planking alone would give sufficient structural integrity. A bamboo pole if dried straight can be split in 8 pieces simply and once fed through a thicknesser you are left with planking with a 45 degree angle on each side. You can butt these together by turning one plank one way and the next the other. Although this hasn´t been used in boat construction as far as I am aware, there are people using this technique to build planes and race bikes with a higher rigidity and strength to weight ratio than carbon and kevlar. I share your thoughts on the poisonous nature and contradiction with Wharrams philosophy, he himself said he hopes one day bamboo could replace these technologies. Although it doesn´t grow in england it could be a sustainable healthy answer to your problems. I am soon going to be in touch with some one who has very successfully used these techniques for other projects and would be happy to share what types of glue to use etc. 

Hope this helps or at least lets you know your not the only one thinking along these lines.

I would definitely appreciate feedback from anyone else concerning this idea