Posted by: Waterbird on Mar-17-13 2:29 PM (EST)
An alterative is to pad the side of the kayak and the underside of the deck so that your knees make good solid contact both outward and upward. That's possible if the width and depth of the kayak are right for your size, and if the cockpit opening is the right size and shape. Short kayaks tend to be wider, and a wide hull makes it hard to contact the sides with your knees, but at 5'9" you should have the needed leg length to stretch out to the sides if the width of the kayak is around 24" or 25".
Each additional one half inch in width is quite noticeable in the speed. 25" wide is pretty slow (in my opinion).