I'm looking for a higher pitch propeller.
I have an 11 and a 13¼ pitch prop.
The 28 HP Evinrude Speeditwin is typically 10⅜ to 10¾ diameter with a .75 (¾) shaft and ¼ shear pin. It seems to be running good at WOT (I still need to run a tachometer on it) as best I can remember from 1970. It runs at 21 mph with a 13¼ pitch prop on a 150 lb 14' tin boat. (So, I think on flat water it should go 3 - 8 mph faster.)