Have your engineer friend add in a layer of glass/epoxy which has a significantly higher strength and see what that does for you. I suspect that most of the wood could be eliminated. See "carbon fiber shaft" at your local paddle shop. My question is "does it really save much weight?" and "is it worth the trouble to do for the weight savings?".

Keep in mind that our town curmudgeon is a CPA, not an engineer. And seeing as it costs more to manufacture a hollow shaft... And as with any given problem there is more than one solution. One may be better for you, another for me. one point we cant disagree on is that some testing would/could be appropriate depending on your intended use of the paddle. Or, you could carry a spare...

: You should refrain from using so many absolutes, George. One must not always
: necessarily maintain the existing diameter. Even a small (and barely
: noticeable increase) in diameter is enough to offset the section modulus
: lost by hollowing the shaft.

: I had a mechanical engineer friend perform the calculation of the ratio of
: original strength to hollow-shaft strength, and nearly one-half the
: diameter of the shaft can be removed from the center, with only a 10% loss
: in strength. By increasing shaft diameter by 5%, this strength can be
: regained. But, I'm sure he's not interested in providing the free labor of
: explaining that to you.

: Does it get no evaluation? No. We just don't tell you that because you're not
: generally party to free and friendly information exchange.

: Whatever.