He will only give you a boat ride one time.
However, when you talk to him again he will ask you if you need a ride and to get in the boat.
The boat is not a solid object and you just fall into the water and you can't click to climb into it either therefore you can't get a ride.
Either this is bugged becasue you can't ride the boat anymore and you should.
This is bugged because your not soposed ride the boat again and he says you can.