Stock Pitch

[greatoutdoors]

Sorry if this belongs in the props forum. Does anyone know the stock prop pitch for a 1970 40 hp Merc 400? Thanks.

[corm]

HI,

There is no such thing as a "stock prop pitch".
Merc shipped the engines without a prop.
The dealer installed the proper pitch prop
for the boat load for the owner.

[greatoutdoors]

HI, There is no such thing as a "stock prop pitch". Merc shipped the engines without a prop. The dealer installed the proper pitch prop for the boat load for the owner.

Thanks. I didn't know that. Obviously the diameter is easy, but is there a way to measure the pitch of a propeller? I know it measures the distance it would move in the water without slippage from 1 revolution, but how do I determine what that no. is? Thanks again.

[steelespike]

Look the prop over for a number on the barrel or under the prop nut.

[greatoutdoors]

Look the prop over for a number on the barrel or under the prop nut.

Ok, there is a 12 and then 180° below the letter A. Would that be the pitch or diameter?

[jeff_smith_0423]

Ok, there is a 12 and then 180° below the letter A. Would that be the pitch or diameter?

It wouldn't be out of the question for that motor to have a 12" pitch prop installed on it. Diamater on those is somewhere in the 10.5's... You can take the prop off and easily measure the diameter.

[corm]

Hi,

Generally there is a no like 48-xxxxx-12 A or just a -12 on the hub somewhere easy to see. This would indicate a 12" pitch prop.

Back in the 60's one of my mechanics had out a way to figure out
pich by the blade height at the hub and the distance from the leading edge to the trailing edge along with some other things I have long forgot that was always pretty close. I should email him for the formula. I remember he sent it off to OMC one time.

[corm]

Hi,
I emailed him for the way he used to figure out the pitch on unmarked props.
Here is what he said.

Corm, If I remember correctly, what I did was to use a protractor to measure the number of degrees between the most extreme trailing edge of a blade and the leading edge at the same distance from the hub center. Then divide 360 by the number of degrees you measured to determine how many times the blade completes its length in one revolution. Next measure the blade height by setting the prop on its base and measuring with a ruler or right angle the height along the propshaft vector line of the same leading edge-trailing edge arc. Finally multiply this number,in inches, by the previously figured number of times it completes its own length and you have your approximate pitch in inches. I say approximate because a cupped edge can slightly mess this up. Hope this helps. Chris

I hope it may help someone out in the future.
Also back than most props were 11 degree rake blades. I asked him if he thought it would work on 15 & 20 degree rake props. I bet he is out in the garage checking it out on his 300HP V8 OMC outboard. hehe

[greatoutdoors]

Cool. Thanks. I did verify it is a 12" pitch, but that info could become useful in the future.