Fatih, IMO, everybody's advice is right on target. My first thoughts were the transmission and brakes when I saw the size of the boat. If you haven't already, the first time you pull the boat up the ramp will give you a fair idea of the power needed to pull the boat. Uphill from a standing start may be the toughest part of this whole deal.
On another note. Please tell us about the boat. Very nice rig and since it has one of the new Evinrude G2's on it (or maybe a pair of them), I'm assuming it's new. Sonar, GPS, weather stations, tell us all about it.
