Why would they need to buy it (and you pay rent) if it’s a free boat?
Someone has to take title, that is, "buy" it for the purpose of registration, insurances, etc. The system doesn't understand gifts.
The "free" boat cannot be insured unless it is hauled out and surveyed, traditionally by the prospective buyer. The boat cannot be berthed without insurance that names the marina as an additional insured. All this is paid by the "buyer."
So "free" really just means less expensive.
Given my financial collapse, that may still involve bankruptcy, I cannot front these costs nor would it make sense to put my name on title if I could. So, my friends will "buy" the boat if it passes survey and I will be a tenant on the boat paying rent sufficient to at least cover monthly berthing, utilities, etc.
Together we will figure out maintenance and repair responsibilities; a sailing schedule, etc. My friends also want to sail and learn improved sailing skills.
If I recover financially and my friends want to sell, perhaps I can buy the boat in the future. If not, my friends will not be in too deep. In any event I get relatively inexpensive living quarters for a while and the opportunity to live on and sail the boat.