Inboard Mercruiser to Outboard on a extension bracket

Discussion in 'Stability' started by MihaS, May 25, 2017.

  1. MihaS
    Joined: Jan 2011
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    Location: Adriatic

    MihaS Junior Member

    Hello ,

    i have question regarding changing inboard Mercruiser engine set with Z drive(Bravo) to BRACKET mounted SUZUKI DF300.

    So my question if this idea is OK, or weight balance of outboard on a 30" bracket will be so much diferent that boat will be dangerous.

    Boat : Sea ray 240ss
    Leinght of new bracket 30" (cca 70cm)

    Weight of SUZUKI engine: cca 300kg

    I hope im in right FORUM, that I get some fine answers.

    Thanks

    Best regards

    Miha
     
  2. Mr Efficiency
    Joined: Oct 2010
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    Location: Australia

    Mr Efficiency Senior Member

    Have you seen any similarly adapted (from inboard to outboard ) ? At a guess, I'd say your centre of gravity will be moved aft. If it is a hull that is inclined to porpoise at all, this will not help. Whenever I see podded outboards with hydrofoil appendages attached, I suspect handling has gone south. 30" is a lot of setback, I would go with the minimum consistent with allowing full motor tilt without the motor fouling the rear of the boat. The positioning of the OB on this boat should help work out where it should go:

    Out reach Sea Ray extends range of power configurations with new 24-foot outboard motor boat http://www.postandcourier.com/automotive/out-reach-sea-ray-extends-range-of-power-configurations-with/article_ab63cfad-10ff-5c54-ba5e-864bc8839a26.html
     
    Last edited: May 25, 2017
  3. CDK
    Joined: Aug 2007
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    CDK retired engineer

    This doesn't sound like a good idea to me. There is a lot of non-structural plastic at the transom of a 240ss, so I understand the need for a giant bracket, but attaching it will be difficult. You probably have to reinforce the whole transom so it can take the engine weight, the static moment of 2100 nM and the dynamic moment from the engine thrust I don't even dare to calculate.
     
  4. JSL
    Joined: Nov 2012
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    JSL Senior Member

    I helped (calculations)with the conversion of a 26' Bertram ( 2 inboards, shaft drive) revised to twin Mercury Verado 300hp. on an Armstrong (Florida) bracket. The results were really good and the client very happy. Yes, the existing transom was of good quality but still had to be reinforced.
    Do your weights/levers/moments to verify the changes so you don't make any significant changes in weight or LCG. In our case we shifted the fuel tanks for'd and this compensated for the engines removal.
     
  5. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    Moving fuel tanks to compensate is not ideal, I have been in boats that performed quite differently when the well-forward. tanks got low, the boat starting to porpoise.
     
  6. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    With the correct bracket design porpoising shouldn't be much of an issue.
     
  7. JSL
    Joined: Nov 2012
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    Location: Delta BC

    JSL Senior Member

    With the Bertram 26 the fuel tank was originally aft and it was moved for'd to where the inboard engines were.... essentially over the LCF so full or empty, the vessel's trim remained almost constant.
    Forward weight bias and bow trim can sometimes cause 'chine walking' ( progressive heeling) which can be quite uncomfortable and potentially dangerous.
     

  8. DonziZ33
    Joined: Sep 2017
    Posts: 2
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    Location: Norway

    DonziZ33 New Member

    Hi Mihas,

    After reading the tread of marinisation of Audi/VW 3,0 diesel engine, it seems like you have great experience of this type of project. You mentioned that you will have your own aftermarket kit for this engine. I intend to install to diesel engines in my Donzi Z33 Crossbow. My budget don't allow me to purchase to new VW 3,0 marine engines, so this marinisation project could be a very good solution for me. Please contact me for more information.

    Thank you in advance.

    Best regards
    Andre
    Norway
     
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