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Information about Propeller?

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arunas

New member
Hello, I would like to know if propellers from different motors would work for my mercury 500 50hp 1972. How do I count propeller sizes and what propeller would be the best for my motor?


Thank You
Arunas
 
Most props have the size stamped in them often seen as 13D 15P as an example, indicating a 13" diameter 15" pitch prop.

Alternately they will have a part number, eg, 48-73140A45.

Then there is a "spline count" (the number of teeth on the prop shaft itself).

Any number of props from various horsepowers will fit any number of motors as long as you get the diameter and spline count correct (too big a diameter and it won't work because it would hit the cavitation plate - too small a diameter and you loose performance because it's not "biting enough water". The pitch will increase or decrease the maximum rpms depending on whether you go with more or less pitch.

What pitch will work on your boat? who knows. You need to find your max rpms with your current prop running the way you typically run (number of people on board, gear etc). If it's in the max range rating for your motor (generally in the low/mid 5000 rpm range on many motors) then whatever diameter/pitch you are currently running is "correct for YOU". If your rpms are below say 5000 - call it 4600 for the sake of argument, then you need to increase your rpms by maybe 600 rpms to get up to 5200 (running wide open). In that case you would decrease your pitch by 3" - so if you prop was the 13D15P that I mentioned you would go to a 13D12P.

If you are getting over 5500 rpms you may want to drop them a couple hundred in which case you would move up to a 16 or 17 pitch prop (of the same diameter).

Increasing or decreasing the diameter by 1" would have a similar effect such that if you get 5200 rpms from a 13D15P you should also get 5200 rpms from a 12D16P prop since you decreased the diameter by 1" but increased the pitch by 1", thus cancelling each other out compared with the 13D15P prop (assuming both diameters would fit your motor).

There is no chart, some guy on the end of a phone or an email response that can figure out "how you use your boat" - even if you and Bob have the same boat and the same motor you could be running different props because you always go out by yourself with minimal gear (more pitch required) and he always goes out with three 200 pound drinking buddies and enough gear to last a week (less pitch required).

Sorry, can't give you a better answer then that.

Looking at the parts list for your motor it came from factory with a prop with a diameter of between 11 1/4" and 10" (11 1/4" D might be the max, I don't have those specs on hand) and pitches going from 10 to 17 which would allow the coverage of a wide range of applications (as I eluded to above).
 
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