Although you can't beat nymack's offer, which I highly recommend you take before you buy, here’s what FL DMV has to say.
"What should the purchaser of a vessel do if he is unable to contact the titled owner to obtain the certificate of title or an executed bill of sale?
Notify the Bureau of Vessel Titles and Registrations in writing stating the existing problem and furnish the Florida registration number of the vessel. The Department will provide the name and address of the titled owner with the necessary instructions for transferring the ownership of the vessel. "
You can also place an offer contingent to a clear title with no liens.
http://www.flhsmv.gov/dmv/faqboat.html