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Thread: Putting 25” shaft outboard on a tritoon that requires 20” shaft...

  1. #1

    Default Putting 25” shaft outboard on a tritoon that requires 20” shaft...

    The boat is a sun tracker 24’ fishing barge xp3 tritoon. Right now it has (and “requires” ) a 20” shaft outboard. But i got a great deal on 150 mercury 4 stroke seapro commercial engine. I know that a jackplate could help the problem by raising it up...but what would happen if i simply mounted it on its highest bolt pattern? Thanks for the input.

  2. #2
    Join Date
    Feb 2014
    Location
    Boat at Lake of the Ozarks Missouri
    Posts
    681

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    Hey phyrefighterjay:

    My initial impression is "Don't do it"

    1.) The anti-cavitation plate will still be too low and cause drag and erratic steering

    2.) The last/top hole in the bracket and transom for this 150HP Merc. may be a weak spot considering the
    torque and stress this motor can place on the transom mount.

    3.) If it is rated for a 150HP then I'm sure it means a 20" shaft.

    4.) Nice price on the engine = poor results on the boat & handling.

    You might be sorry. Sorry !!
    Captain Tony
    2005 Summit by Triton - 220T Platinum 3Log
    2005 115HP Mercury Optimax - 228 Marine Master Trailer
    St. Louis & Lake of the Ozarks, MO.

  3. #3
    Join Date
    Aug 2019
    Location
    Central Texas
    Posts
    127

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    I think the only penalty will be some additional drag while underway and a requirement for additional “draft” considerations while operating in shallow water. The steering shouldn’t be affected except that more effort might be required due to the drag. Try it and let us know.
    2015 SouthBay 522FCR w/150 Yamaha

  4. #4
    Join Date
    Feb 2014
    Location
    Boat at Lake of the Ozarks Missouri
    Posts
    681

    Default

    Still not a fan of your idea.

    The steering drag and effort will be just one issue and because the prop
    will still be too low in the water you may experience problems with reaching
    the power band for this motor. If so, now you are into a prop change.

    Prices on NEW props are steep and may negate the savings you got on
    that bargain engine. Find the recommended RPM range for the 150
    and try to prop into that range.

    Here's an idea though !! Most all engines have a long shaft or short shaft
    version. In most instances the difference is in the drive shaft and/or lower
    unit housing. I remember converting a short to long shaft Merc. with the
    housing and drive shaft for a long one.

    If you are going to add money to your project, why not go the correct route
    with the housing & shaft to go from 25" to 20". It's safer and no compromises. ??
    Captain Tony
    2005 Summit by Triton - 220T Platinum 3Log
    2005 115HP Mercury Optimax - 228 Marine Master Trailer
    St. Louis & Lake of the Ozarks, MO.

  5. #5
    Join Date
    Jul 2006
    Location
    Raystown Country, PA
    Posts
    2,267

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    If it does not have an XL kit the midsection is made for the XL shaft and their is no changing it, at least not easily. I tried it with an XL 125 on my 20 inch transom an it was disastrous, it pushed water everywhere but where I wanted it to.
    1992 Tracker Party barge 24 (new deck, carpet and interior, 2019)
    1996 Mercury 115 ELPTO
    1983 Sea Nymph FM171 Striper
    1985 Johnson 70 J70ELCO

    Raystown Country, PA

  6. #6
    Join Date
    Jan 2012
    Posts
    840

    Default

    What was the out come on this.?
    Malcolm ( Goofy )
    TAP Fins
    8525 Sylvan
    200 H O E Tec




    " Keep a fire in your heart and a smile on your face, for you never know when your leaving this place"

  7. #7
    Join Date
    Feb 2014
    Location
    Boat at Lake of the Ozarks Missouri
    Posts
    681

    Default

    Hi phyrefighterjay:

    OK, Larry has a valid point; not all Mercs have an XL kit when built, although it used to be common practice in production as many engines
    were originally sent to dealers who didn't know what boat they would put it on when they ordered it for inventory.

    How ever, to be certain; can phyrefighterjay share the serial number in a private PM to me and/or Moser and we can look into the build specs
    to determine how feasible or not the conversion might be. In any case, even if not built as an XL production engine it can still be converted
    with the proper short lower unit housing, the short drive shaft and while you are in there, put in a new water impellor and gaskets.

    If the acquisition price on the 150 was favorable then the conversion costs could be worth the money for a safer on the transom powerplant.
    I really don't feel the long shaft installation on that boat is going to be trouble free. It's sort of like the old adage about buying the correct,
    (maximum) HP motor in the first place or you may regret it later.

    Not an exact example but a more satisfying one.

    Good luck - I'd ask a local Coast Guard commander or member for their opinion.
    Captain Tony
    2005 Summit by Triton - 220T Platinum 3Log
    2005 115HP Mercury Optimax - 228 Marine Master Trailer
    St. Louis & Lake of the Ozarks, MO.

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