How to determine a prop's pitch?

I have a prop for an OMC electric shift I/O and am trying to figure out what pitch it is. It is a 14" dia. prop, and the only #'s or markings are on the rear face of the hub. At the 'top' is stamped 'MICHIGAN' and at the 'bottom' is stamped ' P R 1 2 6 ' I've looked on the michigan site and no luck. Is there a way to determine it's pitch by taking measurements or some other way?

Re: How to determine a prop's pitch?

A psychic?

Astrology chart?

Anything?

Bueller..........?
Bueller...........?

Re: How to determine a prop's pitch?

Dia. Rotation Pitch Blades Matl. OEM # Mich #
14 R 20 3 AL 383287 012094

Or You might try this:
http://forums.iboats.com/showthread.php?t=257604

Re: How to determine a prop's pitch?

Thanks alot '72! Is that first set of numbers for my prop above?
I followed the linkee and tried the calc shown there and came up with a pitch of 19.43.

Re: How to determine a prop's pitch?

NW Redneck said:

Thanks alot '72! Is that first set of numbers for my prop above?
I followed the linkee and tried the calc shown there and came up with a pitch of 19.43.

Click to expand...

Yes, the first set of numbers are for your Prop.

Did you measure and calculate each blade?
Did you measure all tip heights?
Are you positive the prop has never been rebuilt and/or worked on?

It is not unusual to find different pitch numbers for each blade. That is what is done when you hear a prop has been labed, bringing all blades as close to the same pitch and rake as they can.

Re: How to determine a prop's pitch?

Thanks for your replies. I just measured one blade before. I'll try all 3 and see what the average is. What do you mean by 'tip heights'? I'm fairly sure the prop has never been rebuilt/modified.
Where did you find the #'s in your first reply?
Again, thanks for your help!

Re: How to determine a prop's pitch?

What do you mean by 'tip heights'?

Blade tip, measured from the table up to the tip of the blade.

Where did you find the #'s in your first reply?

From my 2006 Michigan Wheel Catalog.

Also;
The theory on blade pitch is that at 70% of the blade radius, it is performing 90% of the work.
Therefor, Measure from the center out to the blade tip and multiply by .7, use that number in the equations, instead of the 5".

Cupping generally adds APPROX 1" pitch.
Progressive Pitch Props need to be measured at several intervals across the blade and averaged out to find the Approximate pitch.

There is really a lot more to accurately measuring pitch and rake, My goal, originally, was to help anyone with an unidentified prop to find an APPROXIMATE pitch to start with.

Re: How to determine a prop's pitch?

Great info man, you're just full of it! errrr...uhhhh....I mean.......Thanks!!

I looked all over the michigan website and couldn't get any info on 'PR 126' Is there a crossmatch chart in the catalog?

I'll try remeasuring all three blades using the .7 method and see what I get.

Thanks! Beer's on me!

Re: How to determine a prop's pitch?

For anyone else who may be bored enough to be following this, I'll post the results of my calculations found in the link provided by 72SideWinder. I took a little longer and tried to be as precise as I could.

Blade 1 2 3

H1 4.7 4.75 4.75
-
H2 1.4 1.4 1.35
=
Y 3.3 3.35 3.4
/
X 5.12 5.1 5.15
=
S .6445312 .656827 .6601941
*
31.4
=
Pitch 20.2 20.6 20.7

Avg. pitch 20.5

While looking closely at the prop, there are some verry minor dings along the outer edges of the blades, whitch leads me to believe the prop may have contacted bottom of some kind (probably sand/gravel) I can see the minor distortion can affect the results of these calculations but are still a good way to get into the ballpark on a mystery prop.

Big thanks again to 72SideWinder!


Now that I've got that sorted out, anyone wanna trade my 14X20 eletric shift prop for a 14X18?