Another Prop/Rpm/Speed thread

[THEFERMANATOR]

Originally Posted by roffey

I thought the pitch on the prop was how far the boat will move with one revolution or rotation of the prop. So a 19 inch prop will move 19 inches and a 23 inch prop will move 23 inches. The limiting factor will be prop slip and over or under revving the motor. But as you say there is a bunch more involved and I know I am over simplifying it. I will not hijack this thread any longer, LOL. Thanks for the reply.

In simple terms yes, pitch is the theoretical distance a prop will move itself with one revolution. But as you said that whole prop slip factor is a HUGE factor. Then throw in the problem of some hulls tend to popoise and need a prop to hold the bow down, others ride bow high and need to lift the stern, some run stern high and dig the bow in needing more bow lift. So when you throw hull drag into the equation, on top of getting the engine into it's power band, prop slip, and so on, propping can get confusing. Some people put on trim tabs to make a boat work and run right, but this adds drag from the tabs being used to plant the bow. It's all about setup. I've gone from a 15 pitch in one style prop on a boat, to a 19 pitch with another styke prop on the same boat, with both turning the same WOT RPM.

[roffey]

Thanks for the info. I was thinking of re propping my boat but think I will keep what I have. My boat on a nice day with a little ripple on the water will run with about the last foot of the 20 foot hull in the water and is smooth to the point it is smother at WOT than another speed. My RPM is 4900 and 54 MPH on the GPS. Motor is a 4.3 TKS (2 BBL). Once again sorry for the hijack and thanks for the input Therm.

[THEFERMANATOR]

Originally Posted by roffey

Thanks for the info. I was thinking of re propping my boat but think I will keep what I have. My boat on a nice day with a little ripple on the water will run with about the last foot of the 20 foot hull in the water and is smooth to the point it is smother at WOT than another speed. My RPM is 4900 and 54 MPH on the GPS. Motor is a 4.3 TKS (2 BBL). Once again sorry for the hijack and thanks for the input Therm.

You might could pick up some speed by propping to drop your WOT RPM's a touch as I think that engine makes peak power around 4600-4800 RPM's, but your so close you chance going to far and ruining your performance.