Thread: 40hp mariner

Originally Posted by Bucky75

I am not sure but is this what could have come originally

3 Blade 10.63x12RH Aluminum

That's what CrowleyMarine lists as original for the '87 40hp

Most propellers are labeled with their pitch and diameter, but it is possible to determine both given an umarked prop. The diameter is straightforward to measure of course.

Measurements needed to determine the pitch of a propeller should be taken 3/4 of the way from the hub to the tip.

To measure the pitch, lay the propeller flat on a table, measure 75% of the way from the hub to the tip, and draw a line across the propeller blade. Measure the width of the blade at this point, along the surface of the table (i.e. the width of the blade’s shadow if there were a light on the ceiling overhead). Next, measure the height of the front and the back of the blade, and compute the difference between these two to determine the height.
The pitch is then given by the formula:

pitch = 2.36 diameter height/width

There’s nothing magical about the number 2.36; it’s just 75% of π (pi), because we’re measuring pitch at the 75% diameter mark.
The reason we measure pitch at 75% of the diameter is two-fold. Generally, the pitch of a propeller is not completely constant, varying somewhat from hub to tip to optimize it for the different linear speeds at each point along the blade. The pitch at 75% corresponds roughly to the average effective pitch of the propeller. Secondly, the propeller is sufficiently wide at 75% to allow one to get reasonably accurate measurements of blade width and height.

Thank you Buckeye. I may try and measure the pitch this weekend after I fish. Hopefully figure something out and get one ordered.

If there is a boat service or sales place near you maybe stop in an ask. You can always call Mercury support. 1-920-929-5040.

Have you taken the prop off? The size (D x P) should be on end of barrel where it rides against the thrust washer.

A good prop man can just look at it and tell you what you have. I don't know how he does it. Maybe its from working on them for about 50 years.

My problem is I am out in the middle of a cornfield in IL with the only boat shops about an hour away. Just hoping someone could help with a basic set up. I think I may have something figured out as far as having a backup prop now. Thanks everyone. This is only the second outboard I have used regularly. The other is a 9.9 johnson which has plenty of info on the web about.

If you take the prop off it should be stamped on the back. I’m sure some don’t have it, but I’ve never seen one that didn’t.