Hi there,
I have a Tohatsu 50hp TLDI outboard on my Tohatsu 4.2m rib and with the stock aluminium prop, 11.1 x 13, according to GPS I can hit 39mph at WOT (6k rpm from memory) on my own in the boat. I have looked at the Tohatsu properller chart and it says the maximum I can fit is a 11 x 15...