Hi John, Both of the Pygmy's you are considering are nice designs.

> Put simply, the center of a circular shaft adds very little to strength.
> Here's a couple of data points: Removing half of the diameter is from the
> center of a shaft (e.g, 1.5" OD and .75" ID) reduces the weight
> by 25% with a 0.39% reduction in strength. Removing 3/4 of the diameter
> (e.g., 1.5"OD and 1.125"ID) reduces the weight by 56% with a 10%
> reduction in strength. Is it worth it?

I think so! I'm about ready to try one with about 3/4D removed. I'm also ready to lay up some lighter blades (carbon fiber) to keep the swing weight down.

>That paddle moves up and down a
> lot, and a little of weight savings would quickly add up. I think my first
> paddle will have a hollow shaft, but I'll have to work the numbers to
> decide just how hollow. I'm thinking about doing some destructive testing
> on some samples first just to verify my design too.

The November WoodenBoat had an excellent article on "Bird's Mouth" Hollow Spars. I think that's the direction I'm going to go with my approach to hollow paddle shafts.

My original question was with a weight-saving/effort-saving approach to flat Greenland paddles. I don't think Greenland-style paddles would be as easy to build with Bird's mouth shafts, if you're building the blades with Holst's design.