Why no cold-molded kayaks?

[Dan Wilder]

I'm planning on building a kayak, and I've become curious about the merits of cold-molding for this application. It seems to me that one could build a very strong hull this way, and probably avoid using fiberglass, except maybe for abraision resistance. The result might be lighter than a strip built boat. Has anybody tried it? I've been poking around the ol' internet here and I haven't found anything. Lots of strippers, some stitch n'glue (also intriguing), but no cold-molding. What gives?

[On Vacation]

In cold mould construction of laminates, you need longitual stringers. I don't know of the beast in cold moulded, but the weight factor would be greater than so many of the nice Pygmys or other scarf plywood construction. The typical design doesn't warrant cold moulded construction.

[Ian McColgin]

Given the shape, you need not add the wasted wood and glue of multidirectional cold molding. Lots of very nice stuff with round shapes done strip plank/epoxy.

However, the first kayak I ever got in was an early '60's thing from Germany that was made of three thin layers - 2 ashcroft diagonal and one longitudinal. Cooked, not cold. That was before glass could be done light enough for competative boats and before epoxy made good light home wood work even possible.

If you want a shape that's not hard chined plywood, go strip.

[Todd Bradshaw]

There were a couple canoe builders using modern cold molding a few years back and Gougeon Brothers had plans for a stringerless pram from three layers of 1/8" cedar. I'm sure you could build a kayak that way - but it would be very cost and labor intensive. You would need veneer about 1/16" thick to keep the weight down, probably three layers which involves a whole lot of tedious spilling and fitting and a building mold that has both station forms and is nearly covered with stringers to support the veneer during construction. Building the mold alone would be almost as much work as building a stripper or plywood boat.

There was also a certain amount of public resistance to some of the cold molded canoes from a purely cosmetic viewpoint and the same might be true for kayaks. The diagonal planking looks a bit strange on a long, skinny hull when natural finished. It often doesn't do much for the lines of the hull - or doesn't seem to have anything whatsoever to do with the lines of the hull, which is basically true. People tend to look at the boats and ask "Is that real wood?" - which doesn't seem to happen on a stripper.

[ 08-14-2002, 02:50 PM: Message edited by: Todd Bradshaw ]

[Dan Wilder]

Todd,
I was thinking about using 1/16" veneer, and running the outer ply fore and aft, to eliminate the admittedly hideous diagonal planking appearance. The form would be a big problem, I suppose (although the initial pain in the butt would diminish if I were to build several boats). I was also wondering about vacuum bagging to decrease the total amount of goog in the hull. I realize this whole idea would be a lot more complex/time consuming than a stripper, but it would produce a unique and potentially better boat, so I may give it a try...I'm a mere hobbyist, so production time isn't huge concern for me.

[Billy Bones]

Don't forget too that Joel White's Bangor Packet pulling boat was designed for cold molding. While not a kayak, it's hull form is similar, and the only one I've ever seen was painted.

FWIW

[Todd Bradshaw]

I don't know if you can work fast enough to bag the whole hull. I haven't tried cold molding (every time I consider it, I read the directions and it sounds like way too much work to be practical for the project) but the farther you get from a cylindrical shape the more cutting and fitting you have to do to the plank pieces. It would seem to be one of those "one plank at a time" jobs, though you might be able to fit them all with temporary staples or something holding them down while you shape the pieces and then glue the whole layer at once. Sounds kind of risky, but I don't know.

To bag the whole boat, you would also need a solid, airtight mold - like building a stripper or another cold molded hull just to make the real one on and it has to be thick enough that the staples don't punch holes in it. Better be sure you really like the design of the boat, 'cause you're going to be seriously committed to it. It would make a very interesting boat though.

I have a feeling that a non-bagging approach with a mold that has stringers spaced about 1" apart and careful workmanship might turn out almost as good a boat as bagging it. I've paddled touring kayaks from the 30-35 lb. range up to about 60 lbs. and in the water, I never thought the weights made a tremendous difference compared to all the other factors that either make you like or dislike a particular boat. I did have one slalom racing boat that only weighed 16 lbs. and you could certainly feel the difference in swing weight on the ends when spinning it, but not when just paddling along.

Got any yaking buddies? With a group of four or five builders, you could co-op the mold construction costs and start cranking out hulls.

[On Vacation]

Todd, weight is more of an issue when it comes to carrying it. We go in very remote places and long haul to the marshes makes for a loss of fun. It is possible but a strip design will get into the water faster than any cold mould one.

[George Roberts]

I guess that the first thing you do is compare the strength to weight of the various methods.

3 layers of 1/6" wood cold molded lays up to about the same weight as 3/16" wood with 6oz of glass on each side. Low 30# range for a whole boat if done with care. Not particularly light or strong.

Weight bothers me a bit. I build 20# 17' wood strip kayaks that are as durable as most 35# wood strip kayaks.

I am sure others do better with their methods.

[Konrad in Lincoln]

Not that this is the prettiest thing on the water, but it came to mind...



http://www.stevproj.com/SpecPurp.html

[Bruce Hooke]

If you're after really light weight one way to go would be a 'skin' (canvas or heat shrink dacron) boat. I'm not sure why Platt Monfort only has one kayak design but that approach could produce a VERY light and beautiful, if somewhat delicate, boat -- as the natives in the arctic figured out a long, long time ago...

[John E Hardiman]

Originally posted by Dan Wilder:
Lots of strippers, some stitch n'glue (also intriguing), but no cold-molding. What gives?

This is a topic that comes up frequently as a practicing engineer/Naval Architect. A better question would be: Why cold mold?

Often, customers come in with a page ripped out of the latest NASA Tech Brief and say "I want it made out of (insert latest high tech material here)".

Like many other fields, there is usually a compelling reason to use one material or method over another. If you want to cold mold a kayak, go right ahead... but as an engineer/Naval Architect I would say that I can't recommend it. Like the Corn Palace, it would be an oddity rather than an example of good practice. There are better, faster, and cheaper ways to get the same effectivness.

Like the evolution of the canoe from dugout, to skin/birch-bark, to canvas, to aluminum, to RMP, the evolution of technology trades off against cost and intended use. There is a solid gold bathtub in one Japanese bathhouse. Does it get you cleaner? Someone is willing to pay for it. Are you willing to spend the time and money to cold mold a kayak rather than use developed plywood/ tortured plywood/ strip built? (Hot molding, from the days before fiberglass and epoxy, is very expensive for a one off, but was viable for production runs in the days after WWII when equipment as cheap as surplus.) Answer this question, and you will have your answer as to why there are few if any cold molded kayaks out there.

[Keith Wilson]

Honestly, I think the main reason that there are lots of strip-planked kayaks and very few cold-molded ones is that strip-planking is a lot less work and requires significantly less skill. I haven't looked at the numbers in detail, but I'd guess that cold-molding would not be much lighter or stronger, if at all. OTOH, if you really want one, why not? I certainly can't think of any good reason it wouldn't work.

[Charlie J]

When I was cruising on the east coast in about 1982 or 83, we ran into a couple paddling the east coast and ICW from the New York area down to Florida. They had made it into the Carolinas when we met them. He was paddling a home built kayak made from epoxy and brown wrapping paper.

If he can make one from paper, you can sure cold mold one- Having built a trimaran using coldmolded techniques, I can't imagine the time you'd have in it, compared to a stripper though.

[mmd]

Being a big fan of cold-moulded construction for its superior strength-to-weight ratio and high stiffness modulus, I regret to say that I agree with my professional colleague, Mr. Hardiman. Furthermore, achieving the tight radii and compound curves of a shapely kayak hull with wood veneers would be very difficult, and I believe that given the limitations of the material, you would end up with a hull that would look very similar to a tack-and-tape plywood hull. IMHO, you should opt for either a ply hull if you want stiffness and simple form, or strip-built if you want sensuous form. For examples of nice-looking abd proven design ply kayaks, check out the Volkskayaks by Whynot Boats in the Small Wooden Boat Assoc. of Nova Scotia (SWBANS) website at www.swbans.org . For the pinnacle of what you can do with strip-built kayaks, check out these photos from the Mahone Bay Wooden Boat show:

[Tomcat]

The reality is that some of the very best top of the line racing Kayaks and canoes are cold molded. Though not double diagonal.

If you look back to the older issues of WB, there were several manufacturers who offered double d canoes (back then the Kayak was the odity(. Mason Smith does nice guideboats and canoes in Double D/constant camber, which probably is series produceable efficiently. I think it would be tough to build those sexy fully circular section boats, though I don't see much point in that anyway.

There is a new canoe being advertised that is carbon/veneer cold molded. Jigging must be outrageous.

The problem with Kayaks is that they can be made efficiently using tortured ply or strip. These are the two most effectiuve ways of building wooden boats that we have, so any divergence is probably being done for other than practical reasons. But that sounds like wooden boats to start with.

[garland reese]

Many rowing shells were built in a type of cold-moulded construction, back when wood shells were considered best and fastest (not so very long ago really). The method is a lot more tedious, the jig is much more complex, and the materials would be a bunch (probably) more expensive than strip/composite construction. I think that if you used methods like that of Mr. Roberts, you'd have as light and strong a boat as any in cold moulded construction.
I think it could be done, and would make for a beauty of a boat (with fore and aft veneer outside), with a lot of time, patience, and some extra cash. Joel's recreational shell might be a good example of how to go about it. I would think that the hollows in the ends of most kayaks would be much easier to build in strip, as opposed to veneers. Most rowing shells are really quite simple in their lines, in that they don't generally have any hollow sections in the bow and stern.
Garland
Garland