A boat lift system for raising and lowering a boat from and into a body of water includes a cradle, a cable and a drive system. The cradle is configured to hold the boat. The cable is connected to the cradle. The drive system includes a reel, a drive mechanism and a cable slack control mechanism. The reel is configured to receive the cable. The reel is rotatable in each of a winding direction to wind the cable onto the reel to raise the cradle and an unwinding direction to unwind the cable from the reel to lower the cradle. The drive mechanism includes a drive member and a motor operable to forcibly rotate the drive member in each of a raising direction and a lowering direction. The drive member is operatively connected to the reel to rotate the reel in the winding direction when the drive member is rotated in the raising direction, and to controllably rotate the reel and/or permit the reel to rotate in the unwinding direction when the drive member is rotated in the lowering direction. The cable slack control mechanism is operative to selectively decouple the drive member from the reel while the drive motor is rotating the drive member in the lowering direction.