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Tech Info Request For Lower Unit

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  • Tech Info Request For Lower Unit

    Hey guys...I came across this nifty highly detailed propeller spreadsheet that calculates all kinds of fun stuff. You have to input a few details about your hull and engine. Two questions I cannot answer about my engine:

    1. Number of bearings between gearbox output and propeller
    2. Gearbox reduction ratio (E.g. 1.5)....(is this the same as gear ratio?)

    My engine model number is below.
    Last edited by Jason2tpa; 05-18-2017, 12:49 AM.
    Jason
    1998 S115TLRW + 1976 Aquasport 170

  • #2
    Gear box reduction ratio is the same as gear ratio.

    You can go to the parts catalog for your model and it will tell you the number of teeth in the pinion gear and the ring gears. Divide the ring gear teeth number (26) by the pinion gear teeth number (13) to get the gear ratio.

    Given that the propeller is affixed to the propeller shaft, and the propeller shaft is the output, I don't see any bearings between the gear box output and the propeller. I may be misunderstanding.

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    • #3
      Originally posted by boscoe99 View Post
      Given that the propeller is affixed to the propeller shaft, and the propeller shaft is the output, I don't see any bearings between the gear box output and the propeller. I may be misunderstanding.
      I knew my engine gear ratio is 2, I didn't know gear ratio and gear ratio reduction mean the same thing. Thks for clearing that up. As far as question #1, i copied it verbatim. So your answer that my engine has 0 bearings between gear output and propeller must be correct. Curious, are there outboard engines that do have a number of bearings located btwn gear output and prop?
      Jason
      1998 S115TLRW + 1976 Aquasport 170

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      • #4
        Is this calculator just for outboards?

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        • #5
          Point of clarification. Gear ratio does not technically mean reduction ratio. In an outboard motor yes there is a reduction. In some devices however it could be completely the opposite. It could be overdrive, in which case the output is faster than the input.

          Lots of good information on the innerweb as to how gears, pulleys and other such stuff work.

          Gears - How do they work? - Different types explained and compared

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          • #6
            The calculator program does not indicate outboard, inboard, I/O, or all of the above. The program utilizes microsoft excel to execute the computations. You just plug in a few technical details.

            This forum does not allow for upload of .xls files, so I cannot attach the file for others to download. If you're interested and have MS excel software on your computer, PM me with your email address.
            Jason
            1998 S115TLRW + 1976 Aquasport 170

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            • #7
              I suspect that calculator is for many different boat propulsion systems. For bigger boats with diesels there can be several bearings between the gear box and the prop. Steady bearings, through hull bearings (stuffing box) and outside cutlass bearings.

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