Inboard outboard?

Discussion in 'Propulsion' started by stonedpirate, Sep 6, 2015.

  1. stonedpirate
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    stonedpirate Senior Member

    Hi all

    This is probably a silly question but was wondering if anything like it had been done before.

    On a small boat, to avoid putting a hole in the hull for the prop shaft, could you not rig up a series of shafts and gears that go up and over the transom?

    So the drive shafts would all spin from one side of the transom to the other then could be covered with some kind of housing to hide them.

    Hope that made sense :p

    Thanks
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    Driving around a lot of corners, for what gain ? And how does it compare to an outboard ?
     
  3. stonedpirate
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    stonedpirate Senior Member

    The gain of having no holes in the hull.

    Its only 10hp and gets to hull speed without full throttle so a little loss in efficiency is acceptable.

    Compares to an outboard in that the engine is safely inside and can capsize without being submerged.
     
  4. stonedpirate
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    stonedpirate Senior Member

    Also, to prevent rust of gears below the surface, maybe use a belt to drive the prop.

    So shaft to the top of the transom and a belt down the back side
     
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    Have you thought of a flexible drive ?
     
  6. stonedpirate
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    stonedpirate Senior Member

    hmmm

    never heard of it but it looks pretty interesting

    Will look into it

    Cheers
     
  7. Mr Efficiency
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    Mr Efficiency Senior Member

    I actually have here an odd old thing built for the Australian army, that was described as an "outboard propulsion unit" which looks vaguely like an outboard motor, but there is no engine, where it would go there is a box with a fitting to take a cable or flexible drive, from elsewhere, presumably inside a boat. I don't have the cable though. It is quite a complicated piece of equipment, and I doubt there are any left in captivity ! It is of alloy construction, with stainless shafts, and a bronze, left hand rotation prop. Looking at the shape of the leg, it is designed for low speed, being somewhat lacking in streamlining. Might have been used for pushing bridging pontoons and the like.
     
  8. waikikin
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    waikikin Senior Member

    Sounds a bit like a a mud motor but with an extra set of belts, they seem exxy but wind boats through some pretty thick mud.

    Here's a few examples- http://www.wildfowlmag.com/gear-acc...otors_top_mud_motors_for_waterfowlers_110810/
     
  9. FAST FRED
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    FAST FRED Senior Member

    In many places in the world the engine is simply bolted to the top of the transom and a prop shaft sticks aft 10 ft or so.

    No gearbox , small diameter prop and it swivels to steer too.

    KISS
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    I saw something similar being used by Wehrmacht soldiers crossing rivers in an old doco, been around a long time, the"long-tail".
     
  11. stonedpirate
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    stonedpirate Senior Member

    If I were to do it that way I would just use an outboard.

    Would rather submerge a $3k outboard than a $10k yanmar
     
  12. PAR
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    PAR Yacht Designer/Builder

    I've played with flexible shafts and the shafts aren't cheap. In this application, there's no advantage and you're just reinventing the wheel, so why bother. Hull penetrations are a fact of life and nothing to worry about, given approbate maintenance and product selection. An outboard hasn't any hull penetrations anyway.
     
  13. Mr Efficiency
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    Mr Efficiency Senior Member

    The application is a little unclear, but I'd say you are right about flexible drive being an unnecessary complication. It was just offered as an alternative to the mechanical drive idea that didn't penetrate the hull. Hydraulic drive would be similarly making life more complicated than it has to be, not to mention inefficient. This boat seems to be anticipated to go belly-up at some stage, but I don't see how these alternative drives help that situation go smoothly.
     
  14. missinginaction
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    missinginaction Senior Member

    I'm sitting here in the cabin of my 73 Silverton sedan. I installed a PSS (packless shaft seal) as part of the restoration. The seal never leaked when we put this boat back in service last year. I had a very slow leak, about a gallon a day that i never was able to track down. This season after a few weeks in the water she sealed up tight. Completely dry. I can't see any reason to be afraid of a hole in your boat these days.
    Just my experience.
    Best wishes for a nice Labor Day to all the US posters.
    MIA
     

  15. PAR
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    PAR Yacht Designer/Builder

    Folks that are afraid of thru hulls and other hull shell penetrations, simply lack experience with them or possibly had a bad experience with them, which typically isn't the fault of the thru hull, but it's maintenance and who's to blame for this . . .
     
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