All engines and props behaves different in different boating applications. You need to install an induction tach Tiny Tach, Hardline type and go wot with your current prop. Check max rpm achieved with lightly loaded, well inflated & trimmed sib, depending on your final rpm readings you can play with same size diam prop just varying pitch and place the one that gives max top speed. Will sacrifice best hole shot as you can't have best hole shot and best top speed in one prop.
Factory delivered props usually deliver around medium rpm readings stated for a given portable engine. Check Yam 15 min, max wot rpm factory stated parameters and go from there, selecting best prop pitch by blind recommendation could turn into a expensive purchase that could lead to ruining your engine...