Phillip,
I know you were interested in finding out how many Top Hats are still around and were starting to collect pictures of Top Hats on their moorings. I was wondering if you had thought about a FOI inquiry to Waterways. Surely they would have all the registered Top hats in NSW on their database. The equivalent in Victoria and Queensland would also have the data for their states. Might be an easier way to go and could potentially give you very accurate data on the number of Top Hats still in use/registration.
Others on the sight might be able to confirm the feasibility or otherwise of this approach.
Cheers,
Mark