Different states have different laws, but some things are common to all. If/when you transfer ownership, whether for $1. or hundreds of $... or for no $, sign over the registration and the title, and keep copies of all paperwork, including the driver lic. of the purchaser.
Get this in by email/web/snail mail to your state's boat titling agency ASAP and Pronto.
You cannot control what the next owner of your car/boat/aircraft does 30 seconds after they leave your dock, driveway, or runway. Only thing you can control is your liability for the item that changed hands.
(Our YC had to go thru the proper state process to gain title to an abandoned sailboat in our marina. This took some major paperwork and hassle. Finally we were able to legally own it and then hold a public auction. It "sold" for very little money, but we had all the paperwork in order to show the transfer to a new owner of record. Not wholly unexpected when it further changed hands a couple times over a couple of years, and was reported sunk. Really Sad, but that's reality.)