Thread: Proper motor height

What is your max RPM with your average load? What is your motor's max RPM range (per manufacturer's specs). If you are already hitting the top of your manufacturer's max RPM range now with an average load, then you may have a bit of room to play with a higher pitch prop (each 1" of pitch you go up will steal about 200+- RPM). If you aren't hitting at least the midrange of manufacturer's max RPMs then don't even think about going up in pitch - you'll just shorten the life of your motor. As to motor height, since you have a jack plate you should be able to move it up and down to get the best combination of speed and control before you start ventilating. One more thing - be sure you don't run it so high that your water pickup is starving for water. There are low-water pickup kits available for some motors might be available if you ever do really need to get it that high (although getting it that high is normally less about speed than it is about being able to run shallow).

5k rpm is max. I have always been able to hit the max regardless of load and I can't think of any thing that would stop it. I have not noticed it ventilating. My normal operations is to take it up to 4200 as fast as it would get there while pumping the trim up. The trouble is the nose starts bouncing.

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Porposing can be a difficult problem to solve on some hulls. If you are only getting to 5K RPM then you are likely over propped. I would see if your prop dealer would loan you a prop to test that is 1 to 2" less in pitch and has more cup. Cup gives lift.

I'm not sure I understand the term "getting to 5000 rpm". I can .and it porpoise at 4000. I am very interested in your help.

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Originally Posted by catchNgrease

I'm not sure I understand the term "getting to 5000 rpm". I can .
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But, can you get higher? What I'm getting at is that every motor manufacturer will have specs for that motor that includes a max RPM range. You need to be propped so that your max speed is at the top of that range. Let me explain it another way. Take your motor and put a trolling motor prop on it. How fast would your engine turn? It would have so little water resistance that it would "over rev" unless the motor had a rev limiter (which it does have to protect itself). Then, take your same motor and put on a giant prop made for a cigarette racing boat. There would be so much water resistance that your engine would only turn a few hundred RPM even at full throttle. There is an inverse relationship between the "amount" of prop you have and the max RPM a given motor can run. The weight/hull shape/etc. of the boat comes into play too - meaning that a given motor and prop combination on one hull can run at a different max RPM than the same motor and prop combination on a different hull.

All that is to say that for YOUR motor and boat combination, there is only so much prop you can run and still get up to that magic RPM range. The max RPM range of most outboards is somewhere in the 5500-6000 range. That is why I'm asking if you can get above 5K. If your motor is rated for that 6K max and you are only getting to 5K max, you've got WAY too much prop.

Do you have a water pressure guage? If not I would suggest getting one before you blow your motor up. You can raise them to high.

Add weight to the bow.

Yes. It's really not that high. The Scag of the engine is only 1/2 inch above the hull thanks for the concern though.

Originally Posted by striperking

Do you have a water pressure guage? If not I would suggest getting one before you blow your motor up. You can raise them to high.

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