The propellor for my 20HP 4 stroke Tohatsu for a displacement hull is 9.25"x9" and it just reaches max rpm so correctly propped I think. An alternative prop termed a HIGH THRUST prop is 10"x7". Proponents of 4 blade props say they give higher thrust due to the 4 blades and a bigger diameter prop and go better astern as they are more symetrical. I did try another prop with a bigger pitch but it was then 400rpm down on revs and it was a bit too quick on a tickover for comfortable manoervering.
Anybody got experience of 4 bladers or other words of wisdom to steer me towards or away from this idea. Boat is an 8M with an ultra long leg.