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  Prop Pitch vs RPM with twins.

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Author Topic:   Prop Pitch vs RPM with twins.
Plotman posted 06-07-2004 05:38 PM ET (US)   Profile for Plotman   Send Email to Plotman  
Does the general rule of thumb of 1" of pitch = 200 RPM hold true with twins?

I have the black painted stainless Yamaha OEM props with 19" pitch on a pair of Yamaha 130s on an Outrage 22. Current WOT is 6200 RPM, versus an upper end per Yamaha of 6000.

A pair of 20" Merc Laser IIs would appear to fit the bill, but I also realize that things like blade size, amount of cup, etc will also factor into the equation. Can anyone shed any light on how these two props compare at similar pitches (I realize one comes in even increments and the other in odd). Also, would there be a Michigan Wheel prop than anyone could reccomend as an alternative.

David

LHG posted 06-07-2004 06:11 PM ET (US)     Profile for LHG    
What size gearcase do these engines have? 4-1/4" or 4-3/4"?

The even pitch Mercury performance props are only for non CR gearcases, 4 1/4". 4 3/4" props come in odd number pitch.

If you have 4 1/4" gearcases, and counter rotation, Mercury, nor Michigan Wheel & Stilleto, do not have props for your application.

Sal DiMercurio posted 06-07-2004 07:26 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
I would think those 130s would be able to twist 21p props with no problem at all & possibly 23p props provided the engines are mounted high enough to allow her to unwinde her rpms.
I really doubt you would improve the performance by very much by going to performance props, maybe 3 - 4 mph at wot.
Sal
Plotman posted 06-07-2004 10:06 PM ET (US)     Profile for Plotman  Send Email to Plotman     
Thanks Larry & Sal - the merc website says RH & LH rotation, but fails to mention that there are no LH avail for the V4 gearcase (makes sense, I guess, as merc doesn't do CR in th V4 engines....

Yamaha props it is...

David

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