I messed up my old prop. It has no numbers or markings. My boat would do 35.8mph @ 5,500rpm. The factory repair manual said the standard prop from the factory was a 13 1/4 with a 17 pitch so i ordered a new Solas 13 1/4 17 pitch. My boat now does 34.4mph @ 5,000rpm. My boat 'planes' in 4 seconds...