Merc 115 Prop size

[dj01pass]

I have a 2004 Merc. 115 ELPTO w/ a stock 4 blade stainless thruster prop 13 1/4 x 21P
This is mounted on a Ranger 175VS Bass Boat and is the recommended prop. The problem is that at proper trim w/ 2 guys and gear I am only seeing @ 4700 rpm and by myself @ 4900 rpm.
Max rating on this outboard is 5250 and I would like to see the RPMs higher.
My thoughts were to get the prop reworked to either a 19P or a 20P. How many RPMs in general can I expect to gain per inch of reduced pitch?

 

[Chris1956]

Re: Merc 115 Prop size

A one inch decrease in pitch should raise the RPM ~200. You would therefore need a 2" drop in pitch to get close to max RPM.

If you can raise the motor up on the transom, you might gain some RPM.

You might like to post this in the props section of this forum.d

 

[WillyBWright]

Re: Merc 115 Prop size

Don't push the RPMs on that motor. They snap crankshafts. 5300 is the most I feel comfortable with. Stainless props can be repitched by an inch, aluminums by two.

 

[dj01pass]

Re: Merc 115 Prop size

Thanks! I am not looking to run WOT often , but I don't like the engine to run low RPM either.
I never had a 4 blade before. I like the hole shot and the way it digs in tight corners, but the torque takes a little gettong used to.
I will probably just drop it to a 20 inch pitch and raise it one hole if that doens't get me far enough up. My cavitation plate runs @ 1 inch below the lowest chine on the boat.8)

 

[OldMercsRule]

Re: Merc 115 Prop size

Thanks! I am not looking to run WOT often , but I don't like the engine to run low RPM either.
I never had a 4 blade before. I like the hole shot and the way it digs in tight corners, but the torque takes a little gettong used to.
I will probably just drop it to a 20 inch pitch and raise it one hole if that doens't get me far enough up. My cavitation plate runs @ 1 inch below the lowest chine on the boat.8)

Your Cav plate may work better nearly even with the bottom of the boat. JR