I have seen one of these on the water before, here is one for sale on Ebay, VW engine and all.
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=6472&item=2442133153
I had thought a while back about putting a 996 engine in a boat.
I still think it would be a great powerplant for an express cruiser.