There's more than 4. There is 3 that I know of in Minnesota. It still probably isn't much more than 30-40 boats.

the official history behind the demise of the 5.2 can be found on the unevenly updated nacra class website below

but it won't let me post ba direct link so you'll have to go to the F17 page first and then click "history"

http://www.nacraclass.com/northamerica/NAINDEX.htm

my bad, tedZ already posted the link to that page earlier