Titling and registration are two very different things.
A title establishes ownership, while registration proves that you have paid taxes or use fees in the place where you keep your boat.
Your boat’s registration number is what you see in big numbers and letters on the hull. (often along with a yearly sticker that shows you’ve paid the required fees)
In non-title states, registration is as close as you can get to proof of ownership without an actual title because HINs and owners’ names are included in the document.
While there are several states that don’t title boats, all states require some form of registration. Some states even require canoes and kayaks to be registered.
Vessels that are U.S. Coast Guard-documented (which does establish ownership) must still be registered in most states. Fees collected typically fund state boating programs, resource protection, and maintaining boating access areas.