Brian Nystrom wrote:

Feathered paddles can be shorter (due to different technique used)
and therefore lighter.

How do you figure that? There's no difference in technique that would
require a different length paddle, one way or the other. You seem to be
assuming that there's a difference in paddle placement, paddle angle,
torso rotation, etc. when there isn't.

Hard to describe in words, without a paddle in hand.

With unfeathered blades, your two hands have a paddling motion
in two parallel circles, like cranking two old Model-T starters.

With feathered blades, your shoulders get involved in the strokes
and (with proper personal angle) the wrists and forearms stay
mostly stationary with respect to the paddle. Upper-arm movement
substitutes for a certain amount (10cm?) of paddle length.