How much wear is too much? Racers may want perfect keels, but you can wear the hulls down until the gel is all gone, the keel tip is flat and the flat then takes on a kind of concave. That would be nearly worn through. You repair by laying up 6-8 layers of mat glass and resin. Trim while still green (not yet hard) and then grind or file back to shape. There are keel shape template trawings in the support section of our website.