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| I'm running a 90 horse 4 stroke and my rpms are not up to snuff. What pitch prop should I change to? I'm currently running a 17 pitch. My dealer can't understand why I'm not running at 5500 rpms. I'm maxing out at about 5000 rpms. |
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| What prop are you running? |
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| There are several things I would look at before I went out and bought another prop.
I would start with being sure your tach is correct. I would have your shop check it against their "shop tach". There are several different settings on the back of you tach, if it is set wrong it will not show the correct rpm's.
I would also check how your boat is loaded. Most boats will be less affected by weight in the rear of the boat than in the front. If there is too much weight forward your speed and rpm's will really suffer. If there is too much in the rear your holeshot will suffer. Try running your boat with no fishing gear in it and see what your rpm's are. If you still can't get the rpm's you should have, and your tach is accurate I would then look for another prop.
Every inch of pitch change will equal about 200 rpm's. To raise your rpm's go down in pitch and to lower your rpm's go up in pitch.
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| Thanks Dave. I checked the tac to make sure it was set properly. I ran the boat with just me in it,and little gear and it still maxed out at just under 5000rpm[:(] [:((] |
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| Matt
What kind of boat do you have? |
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| I'd look at the motor hight on the transom first. Most motors should start on the 2nd mounting hole from bottom and work up. When you get the proper motor hight on the transom, your boat will perform better overall, have higher rpms and usually increase hole shot. |
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| To me, it sounds like you might be over-pitched. Even if you move your motor up a couple of holes, I would doubt you would see an increase in 500 RPM.
The best thing you can do is call around to some dealers and find out who will let you run some demo props. Try a few different brands, but I would start with a 15 pitch prop. When you find the right one, your boat will handle well, you will get good lift with a higher rake prop and if the prop is cupped it will bite the water better.
Once you have the best prop, then start playing with motor height. Given that motors have a choice of bolt holes, I would start with the third hole up. If you get excessive cavitation on all trim levels, come down one hole, and repeat the process. Once you get to a point that you can make moderate turns without "blowing out" you will be set with the correct motor height.
I happen to run an aluminum prop on my rig (it's only 50 hp so steel really was out of the question due to lack of choice) called the SOLAS Alcup 3. It has a larger exhaust hub so there is less restriction, which will help to increase HP. The blades are also progressive pitch and cupped throughout to give good handling and excellent hole shot. With this prop, I was able to go up to the third bolt hole off the transom...and might be able to go a 4th...but have yet to try it. I can now turn well without slipping and actually gained about 2 MPH over my stock 17. this is a prop you may be able to stay with the same pitch.
Good luck with the changes...it's a fun job, but can be tedious.
Steve |
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