I have a 25 hp bigfoot merc .I am looking at getting alittle more speed out of it the pitch is 12 . the boat is a 16 foot fiberglass older boat very heavy it will do 40 kilometers per hour converts to about 25 miles acording to my humming bird gps. I am looking at a piranna prop. any suggestions on this prop or any other ideas to get more speed. please help if you can thank you