Check the website of your manufacture for definitive suggestions but usually is on the starboard side approx. 2 inches to the right of the right edge of the prop. You want to make sure there is nothing directly in front of the transducer on the bottom of the boat like strakes, rivets, etc. You want smooth water traveling to the transducer. Mount it so the port side of the transducer is half above the bottom edge of the boat and half below. This can be checked by using a straight edge on the bottom of the boat besides the transducer. Plenty of YouTube videos if you want to see it in action.