Pitch?

[BEARCLAW]

I have a 15hp 4 stroke evinrude with the factory prop that I'd like to replace. Can anyone explain the different types of pitch and what they do performance wise? The motors trolling speed is perfect put lacks a bit on the top end. I can get on a plane, but just barely with two people. Should I stick with the same pitch as the original prop or should I change pitch? Thanks for any help..
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[Kent]

I was hoping that someone more knowledgeable was going to help you out, but I will give you my best shot. BTW -- the pitch is roughly equivalent to the number of inches the boat should move through the water with each revolution of the prop. This is only a rough estimate because of a number of factors. Each outboard is rated to operate within a range of pitches (angle of the blade) and size (diameter) of props. If you exceed the recommended range you could do damage to the outboard by allowing it to run too fast, or by lugging it down too much. If your trolling speed is perfect but you want more speed -- unless you are already on the top end of the recommended pitch you could get more speed with a higher pitch. The issue to consider is how open do you have the throttle now when you are going at the perfect trolling speed. If you have the throttle all the way down already, then you have a problem because you would be going faster than you desire when you troll with a higher pitch. If you do not have the throttle all the way down now, and the outboard will still run at a lower throttle setting, then a higher pitch will probably work for you.
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[BEARCLAW]

Thanks for the info kent. I was afraid you'de say that.. My tiller throttle knob is all the way out (lowest possible setting). I guess it really isn't worth messing with. I'll just replace it with the same pitch... Thanks buddy..[]
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[addicted2fishin]

Basically, to make a long topic short, to increase top end speed, you will also increase your bottom end speed. Unfortunately, you really won't get both out of a propeller change.

Just decide what is most important to you. If it is a fishing motor, I would stick with the trolling speeds.

You may be able to make some changes with slight adjustments to idle speeds, carburation, etc.
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[BEARCLAW]

Fishing is definately more important to me than a higher top end. I probably wouldn't gain a whole lot compared to what I'd have to sacrafice to get it. I appreciate your input addicted2fishin.. Thank you[cool]
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[PREDATOR]

You engine is designed to operate at a specified RPM. By changing your pitch on your prop, you will be changing your RPM. If you go up in pitch, you will drop your RPMs, and if you go down in pitch you will increase your RPMs.

The main thing to consider is your RPMs. Speed, and all that is not important. You may get some speed, but if your RPMS are so high that you toast your engine, you wont have any speed with your new prop.

Unless you know what your owners manual max rpms is, and have a way to guage your rpms, you may not want to change from the factory pitch.

If you want more performance out of a prop, you can get a new one, play around with different diameters, and number of blades, and even pitch, just make sure you have enough information to ensure you arent damaging your engine.
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[BEARCLAW]

Thanks for the advice Predator.. I'll keep the pitch the same as the factory prop. Does changing the diameter or number of blades play a role in engine life and rpm's, like pitch does? I appreciate the info..
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[PREDATOR]

Sometimes going from a three to a four blade prop will increase your rpms just a bit. sometimes going from aluminum to stainless will change your rpms a bit.

As for diameters, the bigger the dia, the more surface area of water you are going to push. And the extra water resistence can add a little stress to your engine, but these things are not such a big deal.

You would most likley be in great shape going from aluminum to stainless, going to a four blade, or increasing your diameter. But I would consult an expert from your engine manufacturer since they have all the available options and understanding of what each option will do for you.

Can hurt to stick with stock stuff though.
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