I went to look at a used boat to work on for a winter project last night. The used boat has an 84 Mercury 150 Black max outboard on a small boat. The boat owner stated the boat did 65 mph but that he almost had thru-hull exhaust installed for the outboard because he had heard a boat with thru-hull exhaust performed better. I didn't ask him how he planned to channel the exhaust from the prop back into the boat and then through the hull.