Out-of-the-box cheap inboard solution design

Discussion in 'Boat Design' started by preventec47, Aug 7, 2016.

  1. nzboy
    Joined: Apr 2011
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    Location: nz

    nzboy Senior Member

    You should have been around in the 70s decade we did all that .Simply get a 1000cc car motor , gearbox and radiator and dump in a boat with universal joints and you have different gears and reverse . Economy model put a briggs and stratton in with washdown hose and hoseclip for connection to shaft .Thankfully we have moved on from those days
     
  2. preventec47
    Joined: Jul 2016
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    Location: Atlanta, GA

    preventec47 Junior Member


    Now THATS WHAT IM TALKING BOUT !

    LOVE IT. not sure it is what I want to do but it is way out of the box.
    So this is what is known as "Longtail" and the guys in quadracep land
    are doing it.
    This may be an omen. Only folks in 3rd world countries are equally budget
    challenged as myself so maybe they had the same needs and this is what
    they came up with to use cheap motors to propel cheap boats.

    Thanks for sharing. This forum is GREAT !
     
  3. preventec47
    Joined: Jul 2016
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    Location: Atlanta, GA

    preventec47 Junior Member

    I see you some of you guys in NZ are kind of snooty about having moved
    on from the old days. I am afraid I am stuck with the lower class bunch
    thinking a car motor with transmission would be a fantastic
    solution especially since todays motors are so much improved !

    Please tell me more about the hoseclip connection to shaft and how you
    ran the shaft through the hull to the prop on the briggs motors.
     
  4. preventec47
    Joined: Jul 2016
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    Location: Atlanta, GA

    preventec47 Junior Member

    What would be helpful and knowledge we can piggy back on is what
    gearbox ratio reductions are popular on outboard motors in the 2hp
    to 30 hp range. For similar applications we should try to copy the
    outboard motor guys.

    For some slower chug chug displacement boat operations like sailboats
    or utility non planing cargo or passenger haulers we could select a higher
    ration slower turning but bigger prop for best efficiency.

    I have not ever shopped for an outboard motor but you would think they
    would offer some with different ratio gearboxes and different size props.
    Does anyone know if they do ?
     
  5. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    We all did this sort of thing, when we didn't have money or a clue. I remember seeing and building many a Chevy 6, with a 3 speed trans and clutch, shafted and hanging a big wheel. You didn't use the gears, just the one that worked with your wheel reduction requirements. None of this is difficult, though you do have to get out there and break, I mean try stuff.

    Toss your lawn mower engine in a boat, any boat, cut a hole for a shaft, screw the reduction, just leave it direct drive, figure out how to steer it and seal the shaft and you're good to go. Melon farmers around the world, have done this for generations. There's no book or online reference, just JimBob engineering, some welding and hopefully small easily handled leaks.

    Of course, outboards can have different gear sets or you can cut up some yourself, which is what the racers do. The choices are market limited, mostly regular or high thrust offerings, but the popular class engines do have a mini market for custom gear sets when the rules permit. Bring your first born, they're not cheap.

    Drop your big lawn mower engine on top of a equivalent size outboard lower leg, make an adaptor and bingo, an air cooled B&S, with shifting, steering and controls built right in. No holes in the boat for a shaft, no rudder, no stuffing box, but you do have to be willing to start cutting, welding and figuring it out on your application specific basis.

    On the other hand, you can get on the water this weekend with the used, running 30 HP Evinrude, I saw on Craig's List for $300.
     
  6. SamSam
    Joined: Feb 2005
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    Location: Coastal Georgia

    SamSam Senior Member

  7. nzboy
    Joined: Apr 2011
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    Location: nz

    nzboy Senior Member

    For the economy model you just drill the shaftlog so the shaft is a fairly loose because the wood will swell Then drill out a 4 inch section about 15mm diameter bigger for gland
    packing make a cap for gland packing to screw on .The hose is to connect motor shaft to propshaft with hoseclip to provide a flexible drive .Just be sure to have some spare hose when the prop gets tangled or hits a rock and chews the other one
     
  8. SamSam
    Joined: Feb 2005
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    Location: Coastal Georgia

    SamSam Senior Member

    You can use/adapt a plumbers compression coupling for the packing gland for $10-20. Just throw out the rubber packing they usually come with and put in some graphite rope packing.

    https://www.plumbingsupply.com/bronze-compression-fittings.html

    [​IMG]

    [​IMG]
     
  9. nzboy
    Joined: Apr 2011
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    Location: nz

    nzboy Senior Member

    I know its all romantic stuff looking back but now $100 buys you a bronze stuffing box
     

  10. nzboy
    Joined: Apr 2011
    Posts: 154
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    Location: nz

    nzboy Senior Member

    By saying Ive moved on, I mean the world has changed .Artisans get the same money as someone flipping burgers .Yes briggs are cheap but so to are outboards, $200 buys a 3.6hp chinese outboard In the seventies if a days wages bought an outboard we wouldnt have been mucking around fitting lawnmower engines in a boat. My last lawnmower cost $300
     
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