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Thread: Long shaft o/b too long?

  1. #1
    Join Date
    Jan 2013
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    Richmond, Virginia
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    Default Long shaft o/b too long?

    I'm thinking about buying a 3.5 hp outboard for for an aluminum 12 foot jon boat.

    The a local dealer has the Mercury 3.5ML motors on a closeout sale. These are new, but I'm guessing they are 2015 or 2016 models. From my past experience, this dealer is big and tends to load up on previous year model motors

    the 3.5m is priced at $950 the closeout 3.5ml $700.

    My question: Will the 3.5ML's longer shaft give me trouble?

    additional details that might help.
    Max. recommended HP 5 HP


    the "3.5ML" has a 20" shaft the "3.5M" has a 15" shaft.
    The boat's transom height 15.5
    Skip

    ---This post is delivered with righteous passion and with a solemn southern directness --

  2. #2
    Join Date
    Feb 2006
    Location
    Pennsylvania
    Posts
    7,620

    Default Re: Long shaft o/b too long?

    Can you raise the transom? Is it worth the trouble? Fishing? If so, do you want the hassle of a high motor head? Whatever you do, don't run it with the prop 5" too deep.
    -Dave

  3. #3
    Join Date
    Oct 2009
    Location
    South Puget Sound/summer Eastern carib./winter
    Posts
    13,033

    Default Re: Long shaft o/b too long?

    Raising the transom a bit is always worth the trouble.
    The spark plugs may stay drier for starters.

  4. #4
    Join Date
    Jun 2000
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    Douglasville, Ga
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    3,940

    Default

    Quote Originally Posted by SKIP KILPATRICK View Post
    I'm thinking about buying a 3.5 hp outboard for for an aluminum 12 foot jon boat. The a local dealer has the Mercury 3.5ML motors on a closeout sale. These are new, but I'm guessing they are 2015 or 2016 models. From my past experience, this dealer is big and tends to load up on previous year model motors the 3.5m is priced at $950 the closeout 3.5ml $700. My question: Will the 3.5ML's longer shaft give me trouble? additional details that might help.
    Max. recommended HP 5 HP
    the "3.5ML" has a 20" shaft the "3.5M" has a 15" shaft.
    The boat's transom height 15.5
    Personally I'd stick with the short shaft. I just don't prefer the cobbled together look that will inevitably come with making the long shaft motor fit. Not to mention the tiller height will likely be far less comfortable.
    Tom

  5. #5
    Join Date
    Jan 2013
    Location
    Richmond, Virginia
    Posts
    2,784

    Default Re: Long shaft o/b too long?

    I was thinking maybe I could get by with a 3 1/2 inch lift on the transom. With only 3.5 ho I doubt it would plane. Thoughts?
    Skip

    ---This post is delivered with righteous passion and with a solemn southern directness --

  6. #6
    Join Date
    Mar 2007
    Location
    East Quogue,NY
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    Default

    We need the transom height of the boat for the best answer. It's a " short," I am sure, but often that is a nominal designation. It's actual height maybe 16 or 17-inches. If that's the case, you may be able to use the lower mounting hole on the long shaft motor and make it work.

    Kevin


    Sent from my iPhone using Tapatalk Pro
    There are two kinds of boaters: those who have run aground, and those who lie about it.

  7. #7
    Join Date
    May 2002
    Location
    Deer Isle, Maine
    Posts
    1,120

    Default Re: Long shaft o/b too long?

    The idea of proper outboard placement is to have the cavitation plate be as close as possible to the BOTTOM of the boat.


  8. #8
    Join Date
    Jun 1999
    Location
    N 78 13 E 15 39
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    1,180

    Default Re: Long shaft o/b too long?

    Transom height should ideally equal the outboard's stated shaft length. If your boat's measured transom height is 15.5", I'd go with the 15" shaft - that is the correct shaft length for your boat. No reason to go with the longer shaft. If you raise the transom, it only raises the center of gravity of your boat - although 3.5hp won't amount to much, of course. If you run the long shaft on an unmodified transom you'll only create extra drag from having too much engine shaft in the water and increase the risk of damage from grounding.
    Bundin er bįtleysur mašur

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