1979 115hp in-line 6

[James Berry]

I have a 1979 115hp in-line 6 that runs pretty good. It has a 13.25" x 17 prop. 1st question - Is this the recommended size prop for this motor by Mercury ? Will I get better performance (faster) on the stainless steel vs aluminum. I am slalom skier and need to go about 3-4 mph faster

 

[Chris1956]

Re: 1979 115hp in-line 6

James, The correct prop is one that will allow the motor to reach 5200+ RPM at full throttle and with a normal boat load. Any idea what your max RPM is?

From my experience with that motor, if you have that motor on a 16-18 footer, you should be able to achieve 36MPH or so, easily, with the right prop. What size. type and weight boat do you have?

 

[calvinator]

Re: 1979 115hp in-line 6

Yes, 13.25" is the right diameter prop for that motor.
The Merc 115HP is a great powerplant for skiing, too.

17" prop pitch sounds reasonable. For additional research, go to iboats homepage and you can find props based on your enginer yr/model. They are all 13.25".

But you need to know what RPM the motor is achieving with that prop. To produce max HP, that motor needs to be running at 5500RPM. What is your engine RPM with the 17" pitch ?

 

[mr 88]

Re: 1979 115hp in-line 6

Yes a SS prop will perform better than aluminum.It has less drag,less flex and more lift,the drawback is if your in a rocky area the SS has no give so if you kiss the bottom there is a good chance that your prop and prop shaft will be toast.