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Long shaft 20" versus 25"

Discussion in 'Smaller Boats' started by ronkS2, Apr 16, 2018. Add this thread to a FAQ

  1. ronkS2

    ronkS2

    Joined Aug 22, 2017
    17 posts, 4 likes
    Hunter 240
    US South Florida
    Hey guys had one last question on long shafts 20 vs. 25.

    I have been very happy with my 20 inch shaft on this boat, but have found a few great deals on a 25 inch shaft.

    Anyone have any first hand knowledge good or bad?

    Thanks,
    Ron
     


  2. CrispyCringle

    CrispyCringle

    Joined Sep 30, 2016
    87 posts, 29 likes
    Hunter 23.5
    US Patoka
    The shaft length should place the prop just below the transom so the prop gets a good flow of water, unblocked by the hull. Too short and it comes out of the water healed over or in waves. But you dont want it too long either. The dimension is measured from the top of the transom clamps on the motor to the cavitation plate on the lower drive. They dont always come out even. So, a 20" may be 23", plus or minus.
     


    Last edited: Apr 17, 2018
    ronkS2 likes this.
  3. Fred

    Fred

    Joined Sep 27, 2008
    351 posts, 19 likes
    Hunter H26
    CA Nepean Sailing Club
    Not sure what boat you have but I have a 25” (x)long shaft Yamaha on my H26. I would not want anything shorter. On rough water the prop has surfaced on occasion.
     


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  4. John Tubb

    John Tubb

    Joined Feb 14, 2017
    547 posts, 111 likes
    O'Day 25
    US Guntersville, AL
    I don't think I've ever thought "sure wish my prop shaft was shorter".
     


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  5. Will Gilmore

    Will Gilmore

    Joined Oct 19, 2017
    1,914 posts, 737 likes
    O'Day 19
    US Littleton, NH
    Keep in mind that the longer the shaft, the more torque the lower unit puts on the motor mount per HP. Sailboats are designed for small aux motors as an after thought. Most of them have minimal transom construction for such support. If you are using something below the 9HP range on a 24'. It shouldn't be an issue. However, if you are over that, you should be sure to reinforce your mount with a plate that spreads the stresses out.
    I'm guessing your question stems from some opportunity for a cheap motor just when your 20" shaft motor is looking and acting old. Longer shafts are not better if you don't need them to get your prop in good water.

    -Will (Dragonfly)
     


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  6. John Tubb

    John Tubb

    Joined Feb 14, 2017
    547 posts, 111 likes
    O'Day 25
    US Guntersville, AL
    Will, those are great points. In my case I went to 6hp 4 stroke 25" on my O'day 25 and it works better then the old 7.5 hp 2 stroke 20"

    Also the new motor is a Sailpro model so it has the high torque lower and prop too.
     


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  7. ronkS2

    ronkS2

    Joined Aug 22, 2017
    17 posts, 4 likes
    Hunter 240
    US South Florida
    Do you know how long your shaft is?
     


  8. ronkS2

    ronkS2

    Joined Aug 22, 2017
    17 posts, 4 likes
    Hunter 240
    US South Florida
    I have a 24 foot Hunter water ballast.. Sorry just started typing stream of consciousness last night.
    Never thought about the added torque with a longer shaft, great input.
     


  9. John Tubb

    John Tubb

    Joined Feb 14, 2017
    547 posts, 111 likes
    O'Day 25
    US Guntersville, AL
    Yes, I bought a Tohatsu 6 hp 4 stroke Sailpro 25" extra long motor from https://onlineoutboards.com/ I really wanted the 25" shaft after a season with the old 20" shaft and a couple of rough returns with the prop coming up even with the motor mount all the way down. With the longer shaft I can start it easily in the second drop position which keeps the pull cord at the top of my stern, and then easily drop it all the way down.

    I spent a fair amount of time to pick the 6hp sailpro vs a larger heavier 9.8 hp. My new motor is actually about 10 lbs less then my old one, the 3 gallon tank is nicer then the larger old 5 gallon on so that is more weight reduction in the stern. Finally the sailpro has a different prop and lower gearing unit for torque which works much better then my old motor and is way quieter.

    I see you are a Hunter 240, that is at least 400 lbs less then my O'Day 25 and the built in stern mount from the ones I've seen is very beefy. I'd get a the same motor I have if I had one like yours. Online Outboards is the cheapest and free shipping, I paid around $1500 ish for mine.
     


  10. Rick Webb

    Rick Webb

    Joined Jun 2, 2004
    2,612 posts, 63 likes
    Hunter 23.5
    US Fort Walton Yacht Club, Florida
    I extended the 20" shaft on my 6hp motor to 25" well worth the expense.

    Go with the 25"
     


  11. topcat0399

    topcat0399

    Joined Aug 22, 2011
    966 posts, 62 likes
    MacGregor Venture V224
    US Cheeseland
    +1

    Wish I had an x-tra long shaft for those times I am caught in short chop...
     


  12. Crazy Dave Condon

    Crazy Dave Condon

    Joined Jun 8, 2004
    6,152 posts, 434 likes
    -na -NA
    US Anywhere USA
    On s lake 20 inch shaft is fine but at the coast 25 inch due to wave action. One thing to be concerned about tilt the engine up when you launch and retrieve so it will not drag on the ramp