Originally Posted by Seafari
I've got a Pro Open 550 with a Yamaha 100HP 4-stroke (carby model). Has s/steel 3 blade prop but there's not specs on the prop so not sure of size or pitch. Any idea what revs I should be pulling and speed at WOT on a rig like this if propped and running 100%
An educated guess is it'll be a 13" diameter prop with a 19" pitch and should pull at least 35knots at 6,000 rpm. Being SS it might also be a 17" pitch. It should be stamped on the side of the hub but sometimes can be hidden on the back of the hub behind the prop nut washer.
If it's not revving well over 5,000 RPM at WOT it's overpitched -maybe a 21" prop. Those engines get very unhappy if overpropped.