Pedal boat drives, talk about yours

Discussion in 'Boat Design' started by MarkX, Mar 27, 2010.

  1. MarkX
    Joined: Feb 2010
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    Location: Azores

    MarkX Junior Member

    In my case, a bent shaft arrangement isn't ideal because the whole prop drive has to be retractable/removable in case I need to come in on surf and smack down on a beach, get line tangled around the prop or if I need to paddle instead of pedal. My Kayak/Canoe will need to be a sturdy working boat designed to safely cope with unexpected sea conditions and curious shark nibbles (chewed prop), not a cruising or racing one for relatively smooth water. Shark attack is extremely unlikely but many world record ones have been caught where I plan to fish so I'm designing for peace of mind.

    Maybe the universal joints supplied for socket sets are of use to those who do want to use a shaft at an angle.
     
  2. Guest625101138

    Guest625101138 Previous Member

    You will find universal joints awkward to pedal and prone to breakage compared with a curved shaft.

    I have developed the curved shaft and folding prop to be virtually immune to damage from striking solid objects. It achieves this by being compliant. It simply bounces off things. I struck a number of logs in last year's Murray Marathon and there was no damage to prop or shaft. The previous year with the rigid prop on the curve shaft as shown in the V11 photo I bent the blades twice. In the worst case I has to stop and straighten the blade.

    The set up I now have is less prone to damage and weed collection than the Hobie flappers.

    The attached photos should give you an idea. The spring steel can be curved into quite a tight radius before yielding. If you yield it you can straighten it out by eye so it works OK.

    The prop can also operate without a strut but this limits the ability to reverse.

    The stern mounted outboard shown earlier can be made to kick up as well to protect itself.

    Rick W
     

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  3. MarkX
    Joined: Feb 2010
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    Location: Azores

    MarkX Junior Member

    Looking at your interesting setup in the left pic, I think it could be adapted to a fishing canoe/kayak by making the strut liftable and the angle gear swivelable.
    In fact, a diy builder could use the complete head from an angle grinder (with a bit of modification) as it's above water.


    Other question: I notice that the pedal cranks seem to be very high up from the deck on most boats. Bearing in mind that a fishing Kayak is a workboat rather than a racing machine, what's the minimum distance between pedal and deck one can get away with?
     
  4. Guest625101138

    Guest625101138 Previous Member

    You really do not need to have the strut liftable. Just leave it free to move up so it can ride over bumps. If the blades hit something you stop pedalling and let the prop ride over.

    Average person needs the crank 300mm to get heel clearance if you use cycle shoes. A trained recumbent cyclist can get away with about 250mm.

    I have modified the deck on my latest design to get a slightly more upright seating as most non-recumbent riders find it unnerving. I quite like the very reposed set-up I use because there is more weight on my back than bum. I do not get bum rash like the kayakers.

    Rick W
     

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  5. MarkX
    Joined: Feb 2010
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    MarkX Junior Member

    On a SEA fishing Kayak the prop has to be reachable because line WILL get tangled around it sooner or later for certain. Preferably it should be completely retractable while landing a fish because if it does get tangled it'll probably be lost and you have to clear the prop anyway. If it's a big fish then it could be even more of a problem. If the drive breaks you have to paddle home too.
    With Sea fishing safety has to come first, one can't just swim to the nearest bank. If the weather turns one can't be dealing with line in the prop. There's also stuff like jellyfish, and you sure don't want to clear something like that with bare hands.

    Thanks, I'll probably go for 280mm clearance initially then. This first drive will be a test bed.
     
  6. portacruise
    Joined: Jun 2009
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    portacruise Senior Member

    Hope this helps, see comments above.

    Porta
     
  7. MarkX
    Joined: Feb 2010
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    Location: Azores

    MarkX Junior Member

  8. MarkX
    Joined: Feb 2010
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    Location: Azores

    MarkX Junior Member

    Just won a batch of five dead 9" angle grinders on ebay which I will strip of their bevel gears. Not quite made up my mind yet as to exactly what I will do (so many options!) but I'm leaning towards bevel gears and shafts suddenly, one on the propshaft and one on the cranks with a shaft going up vertical. This would allow for the thinnest skeg, under 19mm or 3/4" with a small bulge where the bevel gears go for the propshaft.

    I have seen the twisted chain arrangement but am dubious about the strength of 1/4" or 6mm chain and the thickness of skeg required.
     

  9. I57
    Joined: Feb 2008
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    Location: Melbourne, Australia

    I57 Senior Member

    Gear Boxes

    I use one of the Involute gear boxes at 1:3.3 ratio directly fixed to the flexible shaft. The setup is simple and straightforward which is less things to go wrong. I have a mounting frame fixed to the boat and bolt the gearbox on at setup to make transport easier. I lift the 8mm flex shaft up by hand to beach the boat and also it enables me to reverse, the prop is 400mm dia.
    I have tried chains and universal joints with varying degrees of success, but my current setup has been the most trouble free. I don't use a skeg on the flexible shaft and have found even with weed wrapped around the hub speed is not greatly affected.
    The involute gearboxes are heavy but they will take a lot of load and are reliable. The cost is about the same as buying a cheap mountain bike.
     

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