Help...Anyone ever use a set of hydraulic motors for pedal drive?

Discussion in 'Boat Design' started by jeremy360, Apr 9, 2008.

  1. jeremy360
    Joined: May 2005
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    jeremy360 New Member

    I have a small homemeade flat bottom boat out of a 5x10 sheet of aluminum. It wieghs next to nothing. However, since it is 3 ft wide on the bottom and has no ribs, its a real bugger to paddle. I want to set it up as a paddle boat for bowfishing (both hands free). I dont care about going real fast or anything. Just as fast as a trolling motor could make it go on medium speed.

    My question is would a set of two hydraulic motors be a better way to go than chains and flex shafts. What would be the best ratio pedal to prop rpm. Whats the best smaller diameter prop (shallow water) It would be for fresh water. This is just an idea but I dont see why it wouldnt work, right?

    Any advice would be helpful.
     
  2. alan white
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    alan white Senior Member

    Hydraulic motors are very wasteful of energy. Possibly half or more of your energy would simply be converted to heat.
    I would suggest you use a chain, which is pretty a high efficiency transmission. However, you must also convert direction to fore and aft, so a belt might be a better (and more water-friendly) choice. Belts can go around corners.
    The prop, to be efficient, will have to be carefully designed. Human propulsion, whether on a bike or a boat, is most efficient at about 120 rpm for average people if I remember correctly. Also, a person in reasonable shape can produce about 1/2 hp for a while.
    A pair of oars are very efficient if a sliding seat is used, which allows the legs to do the work. The boat hull shape is very important. Short and flat-bottomed is a slow shape (punt). Canoe shapes are more efficient. If you've got a slow boat, make sure your propulsion system is at least somewhat efficient or you'll work pretty hard to get anywhere.

    Alan
     
  3. tinhorn
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    tinhorn Senior Member

    Man, I've wondered the same thing. Seems like it would work, but I've been wrong before. Might be a lot of friction loss. I used hydraulic motors on carwash equipment way back in the last century, and I seem to recall a lot of resistance when I'd spin the shaft of one I'd rebuilt.
     
  4. Frosty

    Frosty Previous Member

    Nothing on this planet has got 100% efficiency. If you must pedal things stick to the smallest possible amount of mechanical equipement.
     
  5. jeremy360
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    jeremy360 New Member

    so...

    what about using a low weight oil or even water/antifreeze. I guess most of the friction is in the seals...so I guess air out of the question too. I just dont reall want the prop where it is down below the middle of the boat with no way to raise it up. Chains and belts make it hard to do. PLus I go in some pretty woody rivers. Is there any type of flexible shaft that works good?

    I thought about the flapper type but those arent good is super shallow water whichis what ill be in moslty. Any more advice?
     
  6. alan white
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    alan white Senior Member

    Oil drive systems have been around for a long time. They are useful for infinite ratio systems, like the Vickers pump used in WW I to turn gun turrets. The problem is that when any liquid gets compressed, it heats up. Becuase steel doesn't compress to any significant degree, gears are far less apt to heat up. Goes as well for chains. Belts store energy rather than heating up so much, imparting the stored energy to the driven side after compression.
    Liquid does compress, and when it does, it gets hot. That is why cars and trucks have transmission coolers for their automatic transmissions.
     
  7. tinhorn
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    tinhorn Senior Member

    Y'mean like using a couple of u-joints to poke the shaft out the back of the boat?
    Man, I thought paddlewheels excelled at this - you don't need the paddles any deeper than you'd have a prop.
     
  8. Estimator
    Joined: Apr 2008
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    Estimator New Member

    New Member

    Hello Group
    Did not know you existed until today. Such a shame...cause I just bought a new boat and will be looking for an appreciative buyer for my 1972 IMP Aztec. My wife finds it hard to get in and out of, and that is creating problems.
    My IMP is UT (Texas) orange and in great shape. A 302 Ford V8, with all original upholstery, and in great running shape. Apparently I am the second Owner, other than the interm "dealer" that had it for 3 months before selling to me. The boat was stored and serviced at Hurst Marina, in Austin for 18 years, and never used. I have the original sales flyer with installation and wiring diagrams complete since 1972. The first Owner took great care of it.
    Since finding this group, I am sad...because I like the boat for its very uniqueness and quality. Unfortunately, it is hard to take out 2 & 3 year old grandkids, without fear of breakdown or other calamity. That is why I am moving up to a 2008 boat.
    With all the paperwork I have for this, including ALL wiring diagrams and part numbers, I may be able to assist anyone else with information. E-mail me if you need any of these. Look forward to further communication
    Estimator
     
  9. Guest625101138

    Guest625101138 Previous Member

    Jeremy
    The hull will not lend itself to great performance. I expect that prop power above say 80W would be wasted in making waves.

    I reasonably fit adult male can pump out about 120W continuously. So you do not need a highly efficient system to achieve what you want to do. A hydraulic pump/motor combination should achieve overall efficiency of 70% if you use light oil and wear in the seals.

    If you want shallow water operation then you need a small diameter prop and spin it fast. Typically an 8" prop spun at 8X cadence would be OK.

    My solution for shallow water operation is a chain reduction to a right angle box that connects to a spring steel or high strength aluminium curved shaft. It is quite amazing how much curve you can get in a small diameter shaft. The interesting feature is that pushing propellers are self-stabilising so they do not need rigid support. In my solution I use a pivoting strut that allows me to lift the prop to inspect it or throw of weed. The prop just bounces over logs.

    Here is a picture of one set up:
    http://www.boatdesign.net/forums/attachment.php?attachmentid=15523&d=1187343575

    If you look closely at this video you will see the prop flashing away aligning itself to the flow as the boat turns:
    http://www.boatdesign.net/forums/attachment.php?attachmentid=15524&d=1187343575
    The shaft is 8mm OD 2011 T8 aluminium rod.

    Rick W.
     
  10. tinhorn
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    tinhorn Senior Member

    What's the efficiency of a typical twisted chain?
     
  11. Guest625101138

    Guest625101138 Previous Member

    Less than a straight chain. I have seen results around 97%.

    However you have to look at the overall application. You can have a tremendously efficient propulsion system in a poorly shaped hull and all the power saving in the propulsion simply goes into extra wave making without much increase in speed.

    I would need to do proper analysis to draw an accurate conclusion.

    The Hobie flapping wings are only around 35% efficient in the usual operating range at say 5mph but because the hull does not respond well to speeds above this it is in its groove at this speed with around 100W input and 35W delivered to the hull. The rest of the power is just blades dragging through water.

    Rick W.
     
  12. alan white
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    alan white Senior Member

    Rick W.,

    You say 70% efficiency, and I made an effort to find a small hydraulic drive that stated any efficiency rating, because I consider 70% to be high enough to be viable if costs are reasonable. I am surprised by the high efficiency, thinking this must be due to modern developments, and I wondered if any vehicles like automobiles had used such systems. Then I read of a car that had been set up for hydro drive and it was indeed more efficient than the standard model. This makes sense if efficiency is at least 70%. this is because losses pile up between both gearbox and differential, not to mention bearings, CV joints, etc., to a lesser degree.
    In the case of a human powered vehcle, infinitely variable ratios are at least as significant as frictional efficiency.
    I'd be thankful if you could point me toward a good link for info on a human-scaled hydraulic motor drive.

    Alan
     
  13. riverliver2b
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    riverliver2b Junior Member

    Rick W.....very cool propulsion! did you adapt an off-the-shelf weedeater shaft or is it completely scratch-built?
     
  14. tinhorn
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    tinhorn Senior Member

    No need, thanks - I wanted to generally compare efficiencies of the two. My thinking is that an efficient drive system will also help preserve the engine, which in my own case is well over 50 years old and has suffered serious degradation in performance from neglect and misuse.

    Jeremy may find hydraulics to be just the ticket, however, since he's not looking for high performance, and it must be simpler to design for routing flexible hoses than straight shafts and chains. This could be a fascinating project to watch.
     

  15. Guest625101138

    Guest625101138 Previous Member

    Alan
    I have not looked at any human power scale hydrailics. My figure was based on larger power hydrailic systems. I know you can get small units though so I am sure if you Google hydraulic drives you will find small units.

    Rick
     
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