I think you are very confused about what constitutes a "documented vessel" in the eyes of the US Coast Guard.
"Vessel Documentation" is a national form of registration. Documentation provides conclusive evidence of nationality for international purposes, provides for unhindered commerce between the states, and admits vessels to certain restricted trades, such as coastwise trade and the fisheries.
To be eligible for documentation, a vessel must measure at least five net tons
and, with the exception of certain oil spill response vessels, must be wholly owned by a citizen of the U.S.
No Hobie Cat qualifies for USCG documentation.
You might want to check out this page: http://www.uscg.mil/hq/cg5/nvdc/nvdcfaq.asp#01