: On the last paddle I hollowed the loom to about 1-1/2" past the root of
: the blade. I didn't dare go any farther due to the way the loom tapers
: off.

Does the loom not run thru all the way to the tips? i.e. you taper it off quickly and use different strips to build the blade. Now that I took another look at those photos this does seem to be the case. No way to extend that hollow very far if this is the technique.

But theoretically, once past the step and onto the blade, the strength increases with the width, thus the middle could be hollow. In the shaft part, no forces really except against the plane of the blade, so keeping the strength against these is only real concern. A box shaped cross-cut with the walls perpendicular to the blades being thickest.

This is an interesting problem; where to put the material for the best strength. Looking at any old I-beam, one realizes that strength comes from proper distribution of material, given the expected direction of stresses. Should one push this for a greenland paddle - maybe, maybe not. Is this getting silly?