From a long ago retired USCG boarding officer: US documented vessels have a hull number that is usually on a main beam somewhere in the hull. We always looked for that number to verify nationality/ownership. Vessels without name and homeport and not flying a flag were considered "stateless" until boarded. Most outboards are not documented and therefore don't have to show name and home port. It used to be that documented vessels did not have to be state registered, but now the tax man cometh. Most all states now require that documented vessels be registered, although they cannot make documented vessels display state numbers. I know Florida requires registration for documented vessels, not sure how hard they enforce it though. Here's what Boat US says: "For those who keep their boats primarily in U.S. waters, federal documentation in no way replaces state registration, nor does it exempt boat owners from complying with state laws. In fact, most states require documented vessels kept in state waters for a certain period of time to register and get a state sticker to indicate that the required state taxes have been paid. However, a state cannot require you to carry state numbers, as a documented vessel already has federal numbers.
Documentation is a federal (U.S. only) form of registering a boat with the U.S. Coast Guard and is preferred by many lending institutions because it is currently the only way to get a Preferred Ship's Mortgage. This type of mortgage for a boat loan allows the recording of a lien against the boat (not the person). Documentation as a vessel of the U.S. is also useful for those who plan to spend time cruising in foreign countries.
In order to qualify for documentation, a recreational vessel must be at least five net tons (usually 25 feet or more) and be wholly owned by a U.S. citizen. Any vessel put into commercial service in the U.S. must also be documented. In order to receive the Coast Guard's "Coastwise" (commercial) endorsement, the vessel must also be American-built."
