: Problem: Exaggerated torso twisting and too many hours paddling wore away the
: bone interfaces that hold my lumbar vertebrae in line.

Get plans and parts for a sliding seat for rowing from Glen-L.

www.glen-l.com

Search for "sliding seat" and you should come up with a picture of the unit, and then you can follow their link to get the following part numbers and prices on the price list.

Sliding Seat Hardware 80-206 131.58
Sliding Seat Plans & Patterns 61-409 26.00

When you are rowing you won't be rotating your back, but you will still be able to get out on the water, and maybe go a bit faster than the other boats around you. The Glen-l rowing unit is self contained, so you might be able to just drop it into your existing boat. Probably need to enlarge the cockpit opening, though. Cutting into a perfectly good boat to do this is more traumatic than difficult.

When you row you are moving your back in such a way that you are not in a sitting posture, so the weight is going to be something other than one of the three situations you describe. You may want to try out a rowing machine at a gym first to see if the rowing action puts too much stress on you. If it hurts, stop, and forget about rowing the kayak either.

Paddling with a single blade paddle, while kneeling over a form, as in a racing canoe, might be another option. There is still some rotation involved here, and that could cause some difficulty.

Footpedal power and a recumbent sitting position? I believe Hobie makes ( or made) a bpat that used pedals to drive flapping underwater vanes for propulsion. It appeared to be a rather interesting system. Might want ot check with them.

Hope this helps.

PGJ