stroke rehab with a recreational sea kayak

I have my own 17 foot fiberglass Eddyline Raven sea kayak but currently it is impossible to get it down from my garage, loaded onto my car and then launched into a lake. I rented a sit-on-top recreational kayak from a local park district. Completely different from a regular sea kayak. Good thing I could try one out because they are not worth buying. You are 4-6 inches above the water rather than having your butt below the waterline. This makes for an extremely tippy ride. I had to be constantly engaged in staying upright. This was approx. a 12 foot boat so it had no rudder and since my paddling it not close to even I ended up going in a large circle to the right. I think I paddled for about 20 minutes, by then fighting my spastic muscles had exhausted my left arm. I know this is supposed to be mainly torso rotation but just holding my arms up was enough to tire me out.