pitch question

[joelfuentes115]

i was loking at 4 blade propellers and was told that in order to use one and inch reduction in pitch is recommended but i cant seem to find a 4 blade prop with a 12 inch pitch can i still use a 4 blade prop with a 13 inch pitch or will that cause problems

 

[craze1cars]

Re: pitch question

Nobody can answer this question without your RPM data...and more specifics of your setup.

What are your current RPMs at top speed with your current prop?
What is the pitch of your current prop?
And what is the correct operating target RPM for your motor at full throttle?

 

[joelfuentes115]

Re: pitch question

the pitch of my current prop is 13 im looking for the rest of the info but im having a hard time since my outboard dosen't has a tach and i cant seem to find one for it

 

[craze1cars]

Re: pitch question

Choosing a correct prop is based 100% on RPM. I'm sorry but without RPM data, recommendations for props are simply not possible...

Changing to a 4 blade of the same pitch might drop your rpms 100 or 200, very generically speaking. This varies widely by brand, design, and application. Whether this possible RPM reduction is a problem for your current setup depends entirely on whether your motor is over-revving, under-revving, or correct as it is now....

Boat tachs are usually rather generic. What kind of motor do you have?

 

[joelfuentes115]

Re: pitch question

its a johnson 70ES75 70 hp from 1975

 

[joelfuentes115]

Re: pitch question

by the way thank you for all your help

 

[steelespike]

Re: pitch question

Tachs usually have a switch so you can adjust for the number of poles on the stator.
They can probably help on the E/J forum. There are also induction tachs that can work on any motor and optical tachs as well.