: My university has a large engineering department so I'm taking advantage of
: the composites laboratory in the next couple of weeks.

Let me get this straight: You are at a university (loaded with professors), in the engineering department (loaded with engineers and specialists), and have a composites lab you can use (more toys to play with than any of us can begin to afford).

And you are asking us tyros for advice?

Gee, I guess we should be flattered.

: "This is my idea for
: a paddle: Form a carbon fiber sleeve into a shaft (how small a diameter
: can I go and still have enough strength?),

Carbon fiber fishing poles might be under 1/4 inch in diameter. Carbon fiber archery arrows would also all int that same category. They would be "whippy" but should take the stress of normal paddling. What do you put, about 30 pound of thrust on the paddle at a maximum? I think they would be too small to hold comfortably, though.

Besides, the idea of a paddle loom that is the size of a closet pole in the center, with tiny carbon spikes coming out, to which paddle blades are attached, well, in my mind's eye it just looks awful funny.
You can go with a larger diameter tube -- large enough to hold comfortably -- and make the tube wall thickness as great as you need to give you the flex and strength you desire. (put that composites lab to good use trying to find out the optimum specs) remember that the width of the paddle blade will affect how much the shaft flexes when a certain amount of pressure is applied. a narrow blade will just zip through the water with little resistance, while a big wide blade will have considerable resistance, and if you push hard on it, the shaft will be taking some of it.

: then cover the shaft with a
: thin layer of wood in some way to give it some warmth.

While I like the idea of warmth and a wood covering, I think you'll have a nasty time trying to get the grain on one side of the paddle to come anywhere near matching the grain on the other. and if you don't do a nearly perfect job the thing will look tacky and artificial.

On the other hand, wood "inlay" on the shaft of the paddle, right where your hands grip it, would give a natural feel. No need to cover these areas, or any others with glass if you don't want to. the carbon doesn't ned it, and the wood would be more slippery to grip with the plastic finish. The epoxy alone should bond your layer of veneer very nicely. You'll have a black paddle with blonde handgrips. A bright colored racing stripe or two, painted diagonally on the blades, should set off the ends.

hope this helps, and thanks for the compliment.

PGJ