Can I drop my pitch?

[andy6374]

1976' 22ft mako with a 2.5L 200hp 88' Merc with 1.87:1 gear reductions.

Currently running a 17 pitch Black Max prop.

At WOT I am turning 5200 RPMs at 42-43 MPH. I imagine there is at least 5% uncertainty in MPH even though it is a new gauge and sender. That is only 6% prop slip. I bet I can drop the pitch to 15" and still be under 12% slip.

What do you guys think?

Actually I am surprise that the engine can't spin the 17p higher.

As it is if I am trimmed up a little I can cavitate the prop if I turn to sharply.

 

[Texasmark]

Re: Can I drop my pitch?

6% slip isn't much.....sorta unlikely if you read the stories from the prop guru's on here.

The slip is the inability of the prop to "screw through a solid" with the applied load.....obviously water is not a solid but the theory is there.

So, you either reduce your load on the prop or get a prop that bites and holds better. Dropping the pitch could reduce the load on the prop but it could also slow the boat which normally puts more hull in the water which increases the load.....so you lost.....but you don't know till you run it.

The fact that you are blowing out in turns indicates to me that you probably don't want to raise your engine (which decreases the load on the prop) without a better grabbing prop.

Don't know if the Black Max is alum and cupped or not. If not, a SS with cupped blades would give you much better performance for the same dia and pitch.........one would think.....gotta run it to know for sure. Would also allow you to raise the engine.

HTH

Mark

 

[andy6374]

Re: Can I drop my pitch?

Thanks for the reply Mark.

I guess the title of the post should have been "Should I drop my pitch?"

-I am not going to spend the money on a high tech SS prop, not now at least. Seems silly to buy a $500 prop for an 88' engine, but when I repower I will.

15" pitch will get me to 5500+ RPMs which will really help the engine not run as hard at the entire RPM range and it will also give a better hole shot. It was just curious that the engine couldn't turn the 17p faster.


Mark you are probably right, if I had a nicer SS prop I could probably keep the 17p and increase my RPMs. Would switch from a run of the mill prop to a high tech prop with the same pitch and diamter increase the RPMs 300+RPMs?