Data point #1:

I finally broke a bird's mouth paddle shaft last night. I was teaching a clinic and demonstrating edging and bracing and went a little too far. I was sculling to roll up and whacked the shallow bottom really hard. First, the blade snapped forward (I hit the bottom with the back face of the paddle) and that bowed it enough to rip most of the glass blade off of the tapered end of the shaft, and put a permanent crease in the glass blade. Then, when I tried to roll, the blade snapped backwards , due to original insufficient "rib" bracing on the backside, and the fact that it was now only glued to a small portion of the shaft near the shoulder. It put a lot of pressure on the thin tapered end of the shaft, and split the shaft back about a foot (between the bird's mouth joints, of course!). I switched blades underwater and rolled up.

I will reglue it, and add a tad more backside bracing to the blade. I wouldn't build another one much differently, though. The shaft is strong enough--the insufficiently braced blade simply put too much concentrated pressure on one area. When making glass blades, some amount of wooden stiffener is necessary, or a hollow glass rib (like Werner and Swift use) for stiffness. Solid glass would be way too heavy to make stiff enough.

I'll get some digital photos on Thursday and post them.

Shawn