> Any thoughts on using foam strips to replace wood in strip built
> kayaks?

Check the archives of this board.

> I am considering using rigid urethane foam strips as a subsitute
> for wood. I plan to build a 2 foot kayak test section and some flat
> test panels with 1/4" x 3/4" foam strips. Wood strips would
> be used in high load areas like the shear, coaming and keel. Aircraft
> Spruce has Last-A-Foam urethane/polyester foam with a desity of 6
> pounds per cubic foot. This stuff is less than $3.25 per square foot
> in 3/4" thickness. This foam in densities of up to 18 pounds
> per cubic foot is available.

Pink household insulation material is available in 1/4 inch thick stock. I've seen it supplied as a folded package of approximately 2 foot wide material by 8 or more feet in length. It is folded in an accordion fashion, and has creases every 2 feet or so, but those may not be a serious problem -- they would be fast and easy to fill, and you could use a soft, easily sanded filler.

You could rapidly cut strips from this with a sharp knife or a razor blade. Since the thickness is already set by the manufacturer, you could pick the desired width. For covering large areas with slight bends you might use a strip of foam 8 or 10 inches wide. You could do the bottom of the hull with 2 easily trimmed pieces, and get a hull bottom shape like that of a stitch and glue.

For that matter, you could use the material to make a stitch and glue design.

Instead of drawing the design on plywood and cutting the pieces on a jig saw, run a knife (instead of a pencil) along the curved lines and cut the parts as you ``draw'' them. No kerf, no waste, no sawdust, no powertools. (For the grammerians, the previous sentence has an implied subject, no verb and contains a quadruple negative. Forgive me.)

If yo are thinking of using wood in keel, and sheer, why not consider a design for a skin-on-frame kayak, constuct the frame and sheathe it with the thin foam and a light layer of fiberglass? The foam/glass/resin skin should be light and very flexible. Point impacts would be spread just as in a skin covered boat. You would have a little more wood here, but you would also have the strength of frames, which would save you from the cost of building up layers of 'glass on the hull.

> I am not sure what weight and number of layers of fiberglass
> will be used. I have not done the calculations for what this sandwich
> needs to be. Point loading (like hitting rocks) seems like the worst
> case problem.

Hitting rocks is always a problem. You'll want more layers of cloth on the outside as armor against that. That adds weight. You'll also want more layers on the inside for strength. That adds more weight. You might look at the archives for the layup plans George Roberts uses. He prefers many layers of thin material, and that sounds like it might be good for you here.

Lightweight foams are not as stiff and rigid as cedar or othr woods. You may need more 'glass to get enough stiffness. You would not want it to fold up on you when you first entered it.

> Foams strips would not be as pretty as wood but could be quicker
> to build and lighter.

So you paint the thing. The only reason to use varnish on a stripper is to show off the wood. There are some very nice colors, but everyone seems to use white somewhere. Someone suggested painting the hull bottom white so that it could be easily seen by the rescue helicopters. I could never figure out why they would build a kayak with the assumption that it was more stable when it was upside down.

Don't assume the thing will be lighter than wood. Some foams absorb resin like a sponge absorbs water. The extra layers of glass needed for strength, and the resin that holds it, will be more costly and possibly heavier. Weight wise, this could go either way. Only a test will give you an absolute answer. Fortunately, the materials are pretty cheap, so if you have the time you can do lots of sample panels in a day or two.

As for speed of construction, well, the sanding time would be less. Otherwise, you have to do about as much work with 1 inch foam strips as with 1 inch wood ones. Time to layout and make the strongback and forms would be identical to what you would do for a cedar stripper. Probably they would be the same parts. Ripping strips might be faster. Gluing would be a bit slower as you would want to avoid drips to avoid sanding problems later.

> The deck could be all or partially wood for visual effects.

You call that a visual effect? Aw heck. I was hoping you'ld paint it a nice bright dayglo orange -- so you could be seen by the recue helicopters. :)

Best of luck Paul Jacobson

P.s. If you get this thing built, send pictures -- preferably NOT aerial shots taken from the rescue helicopters.