Well, now you did it -- you gave me an excuse to sing the praises of rowing as a sport. I would highly recommend giving it another try. It's such fantastic exercise and so much fun. Three Rivers Rowing Assoc. is a great club. Is that where you took the summer program? Anyway, why not use a rowing machine (aka "the erg") during the colder months just to see how it makes your knees feel. Most gyms have them, but there's almost never a line to use one! Go easy, though. I have some teammates who've had knee surgery and need to be careful doing erg workouts. Let me know what you decide.
Burn Booster: Ask a specialist to teach you the proper stroke. Keep your back straight and squeeze your shoulder blades together. Initiate backward movement with your legs, keeping the chain parallel to the floor, and concentrate on making the movement completely smooth.
Bad-form Buster: To avoid back and knee pain, don't bend your knees more than 90 degrees, hunch your back, or push up onto your toes. To prevent your knees from locking, don't fully extend your legs. Concentrate on keeping your shoulders over your hips when you pull back; don't lie back on the machine."
I have one of those old piston-type rowers, and managed to kill my knees on it, by over-flexing them under pressure. (I imagine that current machines are much better.)
As for watercraft, I have a high-performance solo canoe, which is similar to a sea kayak.
