[Paddlewise] Detachable skeg

In Derek Hutchinson's book The Complete Book of Sea Kayaking on p. 19 there 
is an illustration of a white-water kayak fitted with a detachable skeg.  The 
skeg mount apparently slips on and off the aft end of the kayak.  Is this a 
home-made or a commercially available item?  What is it made of?  Who makes 
it?

Thanks,
Tony Niilus
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