SAVE YOUR BACK PADDLING !!!
tie a rope from the bow to the center of your paddle!!
This way you dont have to twist your lower back paddling..... you just use a rowing motion !!! :)

I gave up on my kayak building for now and bought a used kayak for fishing this summer.....

see http://intlmerch.tripod.com/id7.html for pictures of:

1880's canoe /kayak sail rig. You erect a 5ft mast, then attach the sail to a 9 or 10ft spar . The spar has a ring in the middle that you hook over the top of the mast, then tie the spar to the bottom of the mast. You use your paddle for a leaboard. ((like a centerboard)). Sailing across the wind, moving the paddle forward of the sails center of effort causes the bow to turn upwind. moving the paddle aft causes the bow to turn downwind.

Note my comfy wooden seat and how I can attach a trolling motor and skull instead of paddling.....and the dolly I made.