I have recently laid my hands on a 4 metre fibreglass whitewater kayak that I want to use for an overnighter/play boat. The trouble is that as I get to a decent speed on the flat, because it was not desisgned for this, it tends to try and change direction right or left! Any suggestions as to change this? A guy at a fibreglass company (I needed to make some small repairs) suggested I glass a keel onto the back end using EVA foam as a core. I am confidant I can do this but any firther advice would be appreicated.