Higher Pitch the lower RPM? Or the other way around

[samm835]

I can't remember which it is, I currently have a 14X13(mercury 115hp). It seems my RPMs are more than they should be. I don't know exactly by how much currently(ordered new tach), but it seems like it is by the sound....granted I know you can't tell by the sound always, but it just doesn't sound correct. So once I get my new tach I can get better numbers for you, but I was just looking at new props and I wanted to know which way to go IF I am correct. THanks

 

[AngelC]

Re: Higher Pitch the lower RPM? Or the other way around

I believe your correct.....The higher you go in pitch, the lower your RPM's will drop. If you drop in pitch you will increase your RPM's. For every inch you drop or raise, it's approx 150-200 Rpm's. Hope this helps.

 

[crb478]

Re: Higher Pitch the lower RPM? Or the other way around

Agree with ^^^

A 13 pitch is not very agressive, what kind of boat is this on? The prop would be more suited for a pontoon or some type of heavy boat than it would be for a fish or ski type of boat. Once you get the tach let us know and we can have a better idea of what might help you.

 

[samm835]

Re: Higher Pitch the lower RPM? Or the other way around

Its on a 24ft Pontoon...I believe I have the right prop.....but man it sounds like its over-revving. I will follow up when the new tach is installed. Thanks

 

[cr2k]

Re: Higher Pitch the lower RPM? Or the other way around

RPMs should be 5500 at WOT with normal load on boat i.e. ice chests, people, fuel, etc.

Higher pitch will lower RPMs and visa versa, but be careful.

Too many RPMs not good, free spinning will damage rods and brgs.

Too few RPMs not good, due to loading of motor and carbon build up which will eventually bang rod brgs. out.

115 Merc is one of their better motors of that era.

CR

 

[Sandhammaren05]

Re: Higher Pitch the lower RPM? Or the other way around

If bearings and rings are very good, just double the oil/gas mix to rev 6000 RPM and higher. Same block as the 150, which was raced turning 8000RPM on tunnels in the 1970s, 1980s.

RPMs should be 5500 at WOT with normal load on boat i.e. ice chests, people, fuel, etc.

Higher pitch will lower RPMs and visa versa, but be careful.

Too many RPMs not good, free spinning will damage rods and brgs.

Too few RPMs not good, due to loading of motor and carbon build up which will eventually bang rod brgs. out.

115 Merc is one of their better motors of that era.

CR