Although it should be noted that many states now do not recognize Federal Documentation. In theory, it is registration for vessels that are too itinerant to be considered based in a single state, those engaged in international or coastal trade, etc. It is also supposed to be the gold standard of proof of ownership.
My boat is documented in a non-title state (Maine). If I were to decide to move to Maryland, the documentation would not be accepted as proof of ownership. I would have to go back to my storage unit in Maine (I'm a full time liveaboard), dig out my original title from Michigan and the whole paper trail of bills of sale since in order to register. I left all that paperwork there because I thought I had the ultimate proof of ownership when the majesty of the U.S. government was put behind my ownership. Wrong.
Although it is enforced rarely, if you have a documented vessel without a state registration, you are subject to a heavy fine by any local cop the minute you cross the border into Florida. This has been covered by Cruisers.net and here:
I'll Never go to Florida Again - SailboatOwners.com
The presents a problem for cruisers like myself since my home state does not have a registration system for documented vessels. Owners of Maine documented vessel are supposed to pay a local excise tax and receive a decal but I've never seen the decal on a boat up there. Florida laws are so poorly explained and understood by the sometimes aggressive local law enforcement that I expect you could spend considerable time and money proving that the decal, which does not come with any state paperwork you can show, constitutes "state registration". It's really local registration.
The only way I can cross the Florida border 100% legally, it to go to Florida
ahead of time and apply
in person at a county tax office for a Florida state registration for which I need to have a physical Florida address, i.e., a street and not a mail box in the county at which I appear to make the application. Note that this is a county function whereas it is not clear that Florida accepts the local Maine excise tax as "state registration".
Obviously, there are lots of Maine documented vessels and others without state registration cruising in Florida without a problem. However, every once in a while, a local cop gets questioned about how much time he's spending running around in the town police boat and needs to go out and bring in some money to justify it. The state registration issue has been used often to fund BIU (Boating In Uniform).
BTW don't bother mentioning the Sojourner's Permit. It's a separate issue and you can't get it without complying with the above.
It is only inconsistent and infrequent enforcement that prevents this whole situation from being a big problem for full time cruisers. As states budgets get squeezed and they look for additional revenue, it will become worse. A wandering snowbird like myself, even with a documented vessel, could have three or more states claiming the need to register due to different requirements, legal residence, 30 day stay, 90 day stay, preponderance of use (Maryland), lack of other state registration (Florida), etc. You can only register in one state so 100% compliance with the law could have you sitting at borders for days while the paperwork gets done. I don't even know when I enter a state whether I might become subject to registration requirements because I don't have any fixed plans. It's crazy.