If the boat HAS a title, you really should pass that to the new owner, needed or not. Who knows where the boat will go next?
Should? If buyer has half a brain, he would not pay, or buy without receiving the title. It is a legal document that says seller has right to sell, and there are no encumberances on the vehicle/vessel.
Buying any car, MC, boat, trailer, etc without proper documentation is a good way to take it up the azz, as I'm sure quite a few ppl have discovered the hard way.