Drive the inboard prop with an o/board?

Discussion in 'Outboards' started by edowns, Sep 15, 2010.

  1. edowns
    Joined: May 2006
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    edowns New Member

    I have an old wooden 18' sailing boat. The inboard engine has failed. I can put an outboard on the transom but it would need to be off centre.
    I wonder if it would be possible to convert the outboard so that it could stay inside the boat and fix up a chain or gear to drive the existing propellor via the prop shaft. I would need to arrange cooling water supplies to the outboard.
    SO, has anyone done this or got any good tips?
    Thanks
     
  2. kenJ
    Joined: Jul 2005
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    kenJ Senior Member

    Why not replace the existing engine. Lots of small diesels out there, whole lot easier than trying to jury rig an outboard.
     
  3. marshmat
    Joined: Apr 2005
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    marshmat Senior Member

    edowns,
    It's possible, but probably not worthwhile. Buying an outboard and fabricating all the brackets to do this would undboutedly cost more than replacing the engine with a similar one.
    A new, Chinese-built 10 hp air cooled utility diesel can be had for $700. A used, overhauled 10 hp Yanmar marine diesel might be $2000 to $3000 if you scrounge around, and you can occasionally find good used small diesels for much less at equipment yards and refrigerated truck shops. I doubt you'd get an outboard and a heap of custom metalwork for less.
     
  4. edowns
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    edowns New Member

    Thanks But I Had Already Thought Of Replacing / Repairing The Inboard And Don't Want To Do That. Fixing The Engine Is Straightforward, With A Top Bar And Lower Bar With A U Bracket Onto The Outboard Shaft. Supplying A Water Feed Should Not Be Difficult Using The Existing Water Supply & Exhaust Fittings. I Can Imagine Changing The Outboard's Prop For A Cog, Putting A Cog On The Prop Shaft, And Adding A Tensioner.
    But If It Was So Simple Someone Else Would Have Done It, Surely?!
     
  5. marshmat
    Joined: Apr 2005
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    marshmat Senior Member

    1) Why do you not want to replace the inboard? It'd be cheaper and simpler than hacking together a chain drive from an outboard.

    2) No, it's not that simple. The outboard's exhaust must be taken care of (it normally exits through the prop hub), among other things, and its cooling pump is embedded in the lower unit- you'd have to remove the entire engine every time you want to check the impeller. Also, you would now have a bulky vertical drive system instead of one that fits under the cockpit.

    3) Do Not Capitalize The First Letter Of Every Word.
     
    Last edited: Sep 16, 2010
    1 person likes this.
  6. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    It's a novel idea Edowns, but not practical for several reasons. The biggest being you'd have two primary battles to contend with; converting the vertical rotational force of the outboard's output shaft to the horizontal(ish) sailboat's prop shaft and second, a transmission to match the engine RPM's with the prop and if you're lucky have neutral and reverse.

    This could be done and I'd preformed crazy things like this in the past, but ultimately, it's just easier and cheaper to use a combination that offers a little more then the outboard engine does, such as a horizontal shaft. When you can by a nice, German made, air cooled 5 HP diesel for $1,500, which would be more then enough for an 18' sailboat, the question then becomes, how good of a fabricator are you.
     
  7. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    Anything can be done. However, not everything is worth doing. Unless you are looking for an expensive hobby, repairing or replacing the inboard is the logical way to go.
     
  8. edowns
    Joined: May 2006
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    edowns New Member

    Thanks for the main tip - not to do it.
    Thanks for reminding me to deal with the exhaust (& if i change the propellor for a cog the issue of drive direction will not be there)
    I had wondered about the compatibility or otherwise of the rpm and different prop sizes.
    No thanks at all for "marshmat"'s third comment. The need some people express in fora to score points at other people's expense rather than engage in the topic (or ignore it) is a the main reason I and others avoid many fora.
    Bye now, for some time.
     
  9. marshmat
    Joined: Apr 2005
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    marshmat Senior Member

    Just trying to point out a readability issue, mate- one that comes up a lot- and slipping in a bit of humour (something which doesn't always cross cultures easily). No offence intended. Your latter point is a valid one and we at BD do try to be better than most of the 'Net on this front....
     

  10. apex1

    apex1 Guest

    The next one.........


    All the valuable input of a member is immediately on the ignore list when a critical comment appears.

    No wonder these people avoid fora, and good so.
     
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