As Kudzu says, if the flex is in the paddling direction, and the unflexing happens underwater, not much energy is lost.
If the unflexing happens upon exiting the water (i.e. you're still pulling hard when the blade leaves the water) then the energy that went into flexing will be lost - it goes into flinging that paddle blade full of water backwards.
Full Size Sail Rig
Gedi Convertible Helmet
|Table of Contents|