Bob Drive Propulsion

Discussion in 'Inboards' started by tom kane, Jan 15, 2010.

  1. dand0_4
    Joined: Jan 2010
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    dand0_4 Junior Member

    Yes it is.
     
  2. powerabout
    Joined: Nov 2007
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    powerabout Senior Member

    How do you handle the vibration caused when the u joint is runnng at an angle?
    Sounds like you need a CV joint instead
     
  3. dand0_4
    Joined: Jan 2010
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    dand0_4 Junior Member

    A cv joint would require the thrust bearing aft of it greatly complicating things. Tom Kanes design with a double ujoint and slip yoke is very nice but more than I need. 99% of the time the shaft will be close to straight. The small time and angles I will be running and rubber mounting should take care of most vibration. From my experience ujoints dont vibrate all that bad unless at extreme angles.
     
  4. Frosty

    Frosty Previous Member

    Uj joints dont vibrate they accelerate and decelerate at an angle that feels like vibration ,--hence the CV joint (constant velocity).
     
  5. tom kane
    Joined: Nov 2003
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    tom kane Senior Member

    Patent laws only cover certain claims of novelty on parts of a system, not the whole shebang. Attached is a drive I built to test the practicality of a "Vessel Pivotal Drive Shaft Mounting " Succesful Patent title. It solved the problen of trailering an inboard boat,going aground and working the shallows.I could test propellers in surface piercing mode and other related ideas.There are so many ways you can design a trimable drive from the basics to top flight racing drives. There are no shortage of shaft seals and drive covers.As the seals can be above water level you dont have slow leaks dripping inside the hull and no alignment problems.The drive fitted into a slot in the hull similar to a boat centreboard case covered on top.
     

    Attached Files:

  6. tom kane
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    tom kane Senior Member

    Universal joints are best and run more quietly at an angle up to 5 degrees on each u/v joint.If the run at an angle they lubricate better than in straight alignment,that is why u/v joints in o/b drive fail.
     
  7. powerabout
    Joined: Nov 2007
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    powerabout Senior Member

    Tom
    Dont forget you steer an outdrive so the joints do get moved.
     
  8. tom kane
    Joined: Nov 2003
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    tom kane Senior Member

    The parts you need for a basic trimmable drive.Twin u/v joints with sliding spline. Self aligning thrust bearing with shaft collet.Greasable water gland. A cv boot or similar to seal moving area which has a very small (tiny) movement up and down and above water level. If you use a torque tube rotational shaft lifts cooling water to gland. A torque tube is better and can be just galvanized water pipe. Spend a lot of dough and you can create great drive a with stainles sleel.
     

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  9. tom kane
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    tom kane Senior Member

    Attached is the UK 1967 Patent I understand that the Bob Drive was derived from. Improvements to and relating to Motor Boats and the mounting Power units thereof.
     

    Attached Files:

  10. dand0_4
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    dand0_4 Junior Member

    Thanks so much Tom, you have been a great help. I love your designs and the info. you have. Dan
     
  11. tom kane
    Joined: Nov 2003
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    Location: Hamilton.New Zealand.

    tom kane Senior Member

    I have quite a few photos of the early Pivotal Drive if you want any. I can not show you what is being done to develop the drive because of possible patent claim problems,but the early models are public domain. With a bit of careful thought you can build a drive in a few weeks. The work involved is well worth the effort. Attached one of many options.
     

    Attached Files:

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  12. powerabout
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    powerabout Senior Member

    Great photos
    The u joints end up at a strange angle when trimmed though.
    I guess if only used at low power and speed when out of line they would survive?
     
  13. EvilBoater
    Joined: Sep 2011
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    Location: NH

    EvilBoater New Member

    I have built that bob drive, That design is featured in BOBP/MAG/14 by Bay of Bengal Programme. I built one of those boats as my first boat. The tilt bob drive works pretty good. it works best if you leave the tilt out of it and just leave it in the down position. although giving up the tilt, eliminates the shallow water capability, I found that leaving it so that it would tilt would eventually break off the positioning stubs. I used a Briggs & Stratton Vanguard 16 H.P. v-twin. It worked awesome until the boat rotted out. (the boat plans don't call for Epoxy or fiberglass) I built a second boat using a similar drive design with twin props, 2 Vanguard 16 H.P. and 2 comet F-N-R go cart transmissions. I still use this boat to go fishing on small lakes and ponds. It's not fast, but it works. The plans for both the boat and the bob drive are available for download for free on the net.
     
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  14. tom kane
    Joined: Nov 2003
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    Location: Hamilton.New Zealand.

    tom kane Senior Member

    This trimmable drive workes the same as the rear wheels on a vehicle running along a rough road or a rotary hoe cultivator or other implement on a farm tractor. It trails along behind the boat and rises when shallows are encountered and is not rigid and works with a cam like action which reduces any shock. You can build it as strong as you need.
     

    Attached Files:


  15. tunnels

    tunnels Previous Member

    Hows this for a drive !!
    This was a boat up on the hard i couldnt resist but take a picture !! South korea 2008 :confused:
     

    Attached Files:

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