After reading this forum for some time and enjoying very much the exchange of information and camaraderie, I joined the group this morning with a question. I have a new 9.9 HP High Thrust 4 stroke Yamaha as a kicker on my boat. I'm finding at high RPM's quite a vibration through the boat. It's stock prop is 11 3/4 (diameter) x 9 1/4 (pitch). I have managed to find a 4 blade high thrust prop by Solas which is 10 inches in diameter x 9 inch pitch, and am thinking this could reduce vibration and keep the same speed. Has anyone had any experience in prop changes on the 9.9 4 stroke High Thrust? Would appreciate any thought on this ... with thanks Prawny