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What do the numbers on the prop mean?

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  • What do the numbers on the prop mean?

    I have a 3 blade aluminum prop with the fallowing numbers on it. On the hub is stamped 48-58422 And then there is a symbol. I can't tell what the symbol is. Lets say the other numbers should be read with the prop on the boat. If so then horizontally there are numbers in large print that read: 586(9) vertically above them it says 1 and then 3. Around the other side of the prop in horizontal small numbers it says: 48-58422A4 and then is says 19P. What does all this mean? Is 19p a 19 pitch prop?

    The prop came on my 2500 pound boat powered by a stern drive Mercrusier 140. I won't be able to get the boat in the water until next summer. And, I did not get it running right yet this last summer after I bought it. But, it seemed to me to only go about 4000 RPM. The book recommends 4200-4500 RPM for a 140. But, the engine is old. Maybe it's only making 120 Hp instead of 140. The book that came with the boat recommends about a 15 inch diameter 23 pitch prop. So why did this boat have this prop on it. It came with ski ropes. Was he trying to get a better hole shot?

    Also, it seems like the motor likes to run best about 2800-3200 RPM. if you get it over 35 she seems to really be working hard. So, why can't I get a prop that performs best at 2800-3200 RPM and then be careful not to over speed it above 4200? Why spin it out to 42 -45 and waste gas and make the engine work harder? It will mostly be used as a fishing boat. If I occasionally want to pull a skier why can't I just put my present prop back on?

    Lots of questions I know. I hope some of you can help me to understand prop design and selection better.

    Thank you for any answers you can give
    Have a nice Day. Caveman Charlie


  • #2
    Re: What do the numbers on the prop mean?

    You are correct about the pitch. The best propeller size for your boat and engine combination is based on the recommended operating range at WOT, which you say is 4500 rpm.

    The goal in prop selection is to determine what propeller style and size will maximize performance for your boat, while allowing your engine to operate in the recommended RPM range. The correct propeller will prevent the engine from over-revving, yet allow it to reach the minimum RPM where maximum horsepower is produced.

    For every 1" of pitch size, the effect will be approximately 200 RPM. Knowing this, you are about 400 rpm (roughly) off, so you should use a prop 2" less in pitch than the one you are using.

    Once your wide open throttle RPM falls within the recommended range of the engine manufacturer, you have a propeller that is suited correctly for your boat with respect to RPM. If you use your boat for fishing, cruising and skiing, one prop probably won't do all three things equally well. It is best in circumstances like this to have two propellers. One to accommodate one set of circumstances and the other to perform best under the different load. It could, in fact, be that more than one propeller would be suitable for your boat and motor combination depending on your usage. It is imperative, however, that the wide open throttle RPM fall within the range specified by your engine manufacturer
    Chris

    Top Secret Files:

    http://forums.iboats.com/showthread.php?t=299680

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    • #3
      Re: What do the numbers on the prop mean?

      Although you feel you are working your boat harder by going up in RPM's, the exact opposite is true. Allowing your boat to reach the recommended wide open throttle (WOT) RPM's will allow your motor to live a long healthy life. Putting a prop on it that only allows it to reach 3500 rpms' is like trying to ride a 10 speed bike up a hill in 10th gear. It really works your motor and will put it in the grave early. The same is true by putting a prop on that allows an over revving condition to occur. Try going down hill on a 10 speed bike in first gear. A correctly fitted prop is a happy median between these two extremes.
      1996 Crestliner 2160 Phantom, 1996 Evinrude 130 HP
      sigpic

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      • #4
        Re: What do the numbers on the prop mean?

        Well, I better get it running right first I suppose before I make to many assumptions. It seems to measure about 13 inches across. There is nothing like that listed in my owners manual

        What does 2 inch less pitch really mean? A prop with a 17 pitch? The man I bought the boat from said it goes 40 with this prop. But, I can't find a 13 inch 19 pitch prop in my owners manual. There is 17 pitch 15 3/4 prop listed. But, it has a top speed of 25 MPH. And, it's for a 25 foot boat. Mine is 17 feet.

        what do all those other numbers mean? And ideas?

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