Re: US States that do NOT use a boat title.
Just because a state doesn't require a title, doesn't make it easy to buy/sell a boat without a title.
I can only speak for Delaware, but unless you are buying from the last registered owner, you will need to show a DOCUMENTED chain of custody back to the last registered owner.
Let's say I'm selling you an old Mako that I have restored. I never got around to registering it. The guy I bought it from never registered it because he bought it from his neighbor as a project boat he never got around to.
You would need not only a bill of sale from me to you, but also the bill of sale I got from the guy I bought it from as well as the bill of sale he got from the neighbor (the last registered owner).
In a non-title state, the registration card is basically your proof of ownership.
In the above scenario, if I was selling you the boat, and couldn't find any of the previous paperwork, you'd probably be out of luck.
If you get lucky and find the expired registration card while cleaning the planter you just bought and get in touch with the original owner and he's willing to help you out, then you just got lucky.
I just went around this with my old boat, which I was giving to my daughter's boyfriend. I couldn't find the old registration card, or the bill of sale I got when I bought it.
Luckily, I found a helpful clerk at a Delaware registration agent who was able to look up my DL number and make me up a replacement registration card.