Just how many sailboats are there in Michigan?

If you are a recreational sailor, harbormaster, or own a sail loft, marina, or boat dealership, you may ask this same question. It is not an easy question to answer. One metric that SailMichigan uses is simply the number of boat registrations in Michigan which are Sail or Sail (w/aux power). It turns out that even these numbers are best guesstimates and have some inaccuracy due to recent expirations, anticipated renewals, etc. With all that said, data obtained from the Michigan state information center in May 2012 indicated that there were approximately 910,400 registered watercraft in Michigan. Of these, 33,632 were sail or sail (w/aux power).

Although this actual number may be more or less, an interesting finding is that the overwhelming majority of boats are under 26 feet LOA, with nearly half being under 16 feet. Who makes up this population? How many (what proportion) are registered "club" boats vs. private owners? What proportion reside on only 1 lake vs. are trailer sailors? More importantly, how can we grow this 3.7% overall boating fraction into something more?

Could these numbers be an under-reporting? Undoubtedly, small boats on private lakes may not feel the need to renew their registrations and larger boats from other states are frequent visitors. However, when looking at the health and growth of sailing, current registration numbers (if available) are probably the closest approximation to actual boat use. What do you make of these numbers?