Hello all, I have a 13' Gheenoe with a 2006 4 Stroke 9.9 Mercury. I have the stock prop, but I was expecting the boat to run faster than 15MPH. Would a new Prop help this? Is it worth the investment? This is the one I was looking at would it help at all? http://www.mercurypartsexpress.com/us/blkmax-9-5x11-rh-p398.html Thanks in advanced.