Hello, Paul-

: No angels, no dancing and no pins needed. Maybe a needle and thread.

: The answer to your ruminations about kayak "skins" is contained in
: the very wording of your pondering: think skin. Original kayaks were not
: hard-sided, but were soft sided. They were covered with animal skins. Now
: we use woven fabrics.

: There is obviously a great deal of difference in stiffness, strength and
: flexibility characteristics between woods and fibers. I wouldn't even try
: to compare them. Nor would I make any attempts at comparing the more
: complicated composite structures with the physical properties of a sheet
: of cotton or dacron fabric.

: Next time you get out your sander for a few hours of mind-numbing work,
: consider the ultimate question: How strong is "strong enough"?

: Since you like to do math in your head, try these numbers: Figure the average
: force exerted on the skin of a fully loaded kayak.

: Since I'm not fond of doing calculus in my head, I'd estimate this number,
: starting by making a few assumptions. First, I'd work with an 18 foot long
: kayak that had a beam of 24 inches, and which drew 6 inches of water when
: loaded with 400 pounds of paddler and gear. That is fairly close to real
: life. Again, to keep the math simple I'd assume this boak had few curvesto
: speak of, and that the hull was shaped like a long diamond, and had
: straight sides rising from a flat bottom. The area of the bottom therefore
: could be calculated as teh area of a diamond 18 feet long and 24 inches (
: 2 feet) wide. A little exmintion of the situation shows that this is the
: same as the area of a rectangle 1 foot wide and 18 feet long, so I
: calculate a bottom area of 18 square feet.

: Now, I could further calculate the height of the sides that are submerged (6
: inches or 1/2 a foot, multiplied by the length of one side of the diamond
: (that would be the hypotenuse of a 9 foot long and 1 foot high right
: triangle, or the square root of 82), and then multiply that number by 4.
: I'll multiply the 1/2 and the 4 first to get 2 and then fugure the
: hypotenuse as a tad over 9, so my total submerged sides would be another
: 18 square feet. So far I have 36 square feet under water, and suporting
: 400 pounds of gera and paddler. I'm going to now simplify things a lot,
: and remember that a real kayak has rounded edges ans not sharp square
: sides. Those curves cover quite a bit less area than what I've calculated,
: so i'm going to round things down to an estimate of 20 to 25 square feet
: of surface underwater.

: With 20 square feet of surface and 400 pounds of contents being displaced,
: the pressure per square foot is 20 pounds. With 25 square feet of surface
: the pressure is 16 pounds per square foot. Now common measurements for
: pressure are in pounds per square inch or PSI. There are 144 square inches
: in a square foot, so, for the smallest area I'm estimating I can divide 20
: by 144 and get a pressure on the hull of a whopping one-seventh of a pound
: per square inch. And for the largest surface area I'm estimating, it is 16
: divided by 144, or about one-ninth of a pound per square inch.

: Those are average loads, but I have tow other matters to deal with. One is
: water pressure. At a depth of 6 inches the water pressure on the bottom
: will be about 1/4 pound or 4 ounces per square inch. That is roughly twice
: the average load given above, and I figure it this way. From my diving
: experience I know that pressure of the water is about 1 atmoshpere, or
: about 15 psi at a depth of 33 to 34 feet (depends on salt- or
: fresh-water). That means that for each foot of depth the water pressure
: increases a bit less than 1/2 pound per square inch. with 6 inches of
: depth I take a half of that.

: Then there is the possibility of connecting with an object. We have to know
: how much weight is going to be concentrated on how small of an area.

: and here is where I leave you to do the rest of the math.

I figured that if I got back on that sander, I'd get in even deeper than I am now.

I did have the day off, though, and it wasn't raining for a change, so I milled a few cull cherry logs I had laying around, and tried to crunch a few. Numbers, that is.

Stress=force/area. If your 400 pound boat hits a rock with a needle sticking out of it, the loads on the hull approach infinity.

After I got that out of the way, Cara and I took the new boats out for her first float. She loved it and was happy, so I'm happy, of course.

And it was strong enough
: Have fun, and concentrate on the sanding

: PGJ

Mike