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Short Shaft Rarities

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  • Short Shaft Rarities

    I'm running a 1992 30 HP Evinrude short shaft O/B on my 1958 Lone Star Nassau (16' Aluminum). It maxes out at 25 mph. I'm looking for a little more top end, so I'm trying to locate a 35-50 HP short shaft motor. Are HP ratings the same, regardless of vintage? Assuming good compression, would a vintage 40 HP motor (e.g Big Twin) really push more than the 1992 30 HP motor, or does improved technology get more performance? (For now, I'd rather stick with existing motor than go the jack plate route to let me run a longer shaft.) Any other considerations? I'm finding that 40 HP short shaft motors are actually hard to find. Thanks much,

  • #2
    Yes they are harder to find.-----Your location may be a factor as well.


    • #3
      Pre-82 motors were generally rated at the crank, post 82 they were rated at the prop.

      your 1992 30 might be lighter then a vintage 40hp, its more fuel efficient and likely to provide nearly the same umph as a vintage 40 would. Theres @10-15% hp lost from crank to prop, so a pre-82 40hp is about equal to a post 82 35hp+/-...

      is your 30 reaching peak RPMs at WOT?

      your Nassau should be rated for a 50-75hp motor, isnt it?

      I think early 90s (late 80s maybe) 50hp Johnson/Evinrudes came in a short shaft....

      Pretty sure I know a guy running 1 w T&T on a 15ft vintage aluminum boat. It hauls arse, even w 4guys @200lbs+ each aboard..... although It is only rated for a 40, IIRC......
      Money spent @ Boat Restoration should be measured in Smiles & Pride SHOP IBOATS-BOAT SPECS-FORUM HELP-REPAIR/RESTO


      • #4
        All other things being equal, the newer motors with thru-prop hub exhaust lower units are faster than the older non-thru hub lower units. The shape is the secret.


        • #5
          Slower turning / higher pitch props are more efficient too.


          • #6
            PM sent
            '47 18' CC Utility "Knock On Wood"
            Various Evinrude powered Pontoons all named "Floosy"


            • #7
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              Thanks so much for the insight. I learned a lot about how HP ratings changed over time. The capacity and HP ratings for the Lone Star Nassau changed from '57 to '58 (40 HP to 60 HP). My original data plate was missing from my "mulch' transom, but some great fellow owners provided me with images of their data plates.
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