No additional speed
Doug, unless your previous prop was the wrong size/pitch you aren't going to gain anything in terms of speed in flat water. Yes, the 3 blade is going to keep you moving if you are battling a strong headwind or waves, but in flat water (typical of your area if I do say so myself) you aren't going to gain anything. Maybe you know that already. The one thing you didn't ask was how much drag are you going to create. You didn't mention feathering so I'll assume you are talking about a fixed prop. Expect to lose 1/2-3/4 a knot in light air (typical breeze for Olympia?) and less as the wind & boat speed increases. I hope you aren't expecting to get the performance of the newer 27hp 33.5 by putting on a 3 blade prop. It isn't going to happen. Is more power in reverse really that important. Seems like it would be a whole lot safer and less expensive to just ease into places slower in forward rather than rely on reverse power that may not be available everytime (engine dies?). Maybe I've gotten your motives wrong. Just trying to save you some money. 3-blade fixed props are not my idea of a good investment. Buy a spinnaker instead and then you won't have to motor with that 2-blade as often. Vibration - do you only notice vibration when the shaft is turning. I would think a lot of the vibration is due to the 2 cylinder engine itself. Maybe that isn't it? Not trying to offend. Just trying to help.
