Check out this theory:
The man on the boat is Kelvin. Why? Simply because both Desmond and Sayid are going to the boat and BOTH of them will remember Kelvin from their past.
Something interesting about the rocket thing, it should have taken a minute to get there but instead took 31 minutes. So perhaps it went back in time or something which took 30 min but I don't want to divulge in time travel crap.