Pedal Boat Design

Discussion in 'Boat Design' started by BG_Geno, May 28, 2006.

  1. mattotoole
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    mattotoole Senior Member

    I think you're a bit optimistic. 1 HP = 750W. A fit recreational cyclist (one who rides 1-200 miles/week, and perhaps competes occasionally) can generate about 200W sustained for 3-4 hours, with short bursts about twice that. These figures can be approximately doubled for elite/pro cyclists.

    Common wisdom has traditionally considered human output to be about .25 HP.

    --
     
  2. BG_Geno
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    BG_Geno Senior Member

    Yes, a 90 degree spiral beveled gear like the one linked below. The other I am concidering is for the 2 person boat and is the 3 way version.

    http://www.mitrpak.com/product_datasheet.php?product_id=27

    Poida: I concidered the design where the riders sit opposed and a direct drive is used, but the biggest issues with a design like that are the sitting sideways while moving forward, the need for both riders to be the same weight ( I am 200 pounds, my wife is 100 pounds for example) and the simple lack of areo dynamic elegance =)
     
  3. BG_Geno
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    BG_Geno Senior Member

    Your prolly right. I used the research data from the human powered flight program at a major university and those were their numbers. They also won the human powered submarine contest and did a lot of research with all those brain trusts monitoring some guy on a stationary cycle...hardly real world.

    Geno
     
  4. mattotoole
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    mattotoole Senior Member

    These projects usually employ a top-notch cyclist, so the numbers you've seen are not surprising. So much of this info is available that it's actually hard to weed through! You might try www.ihpva.org. They're focused on maximum performance too, but some folks there probably have a good idea of what output to expect from various kinds of users.
     
  5. BG_Geno
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    BG_Geno Senior Member

    We actually catch a break in a few reguards though.

    In the human powered aircraft, propulsion (moving the pedals at very near maximum human output) is mandantory. Stop pedaling and you stop flying--don't pedal fast enough and you also stop flying. For our use, if you stop pedaling you will continue to move forward for a short time at least--just as a canoe does not stop the second you stop paddeling. Also, if your "output" is less due to less capable physical specimens, or fatigue etc., you just travel slower.

    When you choose to use a human, or 2 humans as the engine, your design choices become limited in some areas like how that power is actually translated to forward motion--paddle wheel, submerged prop or areo prop. To me as the designer, builder, and ultimatly as the engine, the other factors are far less limited, but share the same common threads. If one pair of "engines" can combine for 2 HP or only muster 1 HP the boat still needs to have an efficient hull design, efficient and adaptable seating and propulsion.

    I am told by my cycling friends that efficient pedaling is using a tempo or cadence (80 to 100 RPM) and just staying there despite terrain variations. Change gears for up and down hill to maintain that tempo. As our use is on perpetually flat terrain (yes head and tail wind will come into play) we can forgo the huge range of gears needed and simply gear the pedal to prop RPM ratio for that optimum say 90 RPM.

    Build the best boat I can. Efficient power train and prop...then start pedaling and performance will improve =)
     
  6. Poida
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    Poida Senior Member

    Bg I would have thought for the prop to be efficient in forward drive, it would be just as efficient in resistance in forward motion if you stopped pedalling. Of course you could experiment with collapsable blades on your prop that close up if ther force of the flowing water is more than prop rotation. They would open up when the prop starts turning.

    I am surprised by the need for such high precision in the gearbox. It looks as if would be oil filled, which in itself would add resistance to the gears as well as the need for oil seals on the shafts also reseisting rotation. It seems to me, too much energy would be lost.

    Surely a pulley between the pedals and a twisting belt driving a 90 degree axis pulley on ther prop shaft would be a greater energy saver. And a lot lighter than the 2 pound gearbox.
     
  7. BG_Geno
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    BG_Geno Senior Member

    The prop arm or "gear head" for want of a better word pivots and can be raised completly out of the water. When I get the design a little further along I will post some sketches.

    Geno
     
  8. BG_Geno
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    BG_Geno Senior Member

    Design Update

    Well Guys, here is concept 3...yes those are paddle Wheels...

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    The problem with a prop boils down to draft. The minimum dia for props is 16in with 20-24in being optimum. That means I could not use the boat in the locations I want to.

    Of course the seats, chains etc are not shown yet (have to design the seats still. As you can also see, its a tandem pedal boat now. Overall length is 18 feet, length at the waterline is 16' 11" and waterline width is 9". (each of the two hulls. Total weight is still projected at or under 100 pounds (just boat, no riders/cargo). Comments?

    Geno
     
  9. Poida
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    Poida Senior Member

    Hi Mr Geno
    Paddles, hmmmm, hate to say I told you so LOL.

    I reckon that with the paddles that you have there, you would lose too much energy putting the paddle into the water as it gives a downward thrust rather than longitudinal. Similarly as the blade is exiting the water.

    I think that the propulsion could be improved by having more blades in the water at one time pushing longitudinally.

    I'm thinking of a geared belt as used for power transmition with stainless blades bolted to it, travelling along 1/4 to 1/2 of the boat length. The spacing of the blades would be set so as to not allow the following blade to be running in the cavitation caused by the preceding blade, a problem that I feel would be experienced by the type of paddle you drew.

    Also will keep the hight of the paddle down so as not to be effected by the wind, another problem I can see in your design.

    Cheers
     
    Last edited: Jun 19, 2006
  10. BG_Geno
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    BG_Geno Senior Member

    You LOVED saying I told you so =)

    I scoured the web looking for resources on paddle wheel design, and there was not much. What I did find suggested a few things; Design the paddles to be most efficient at speed, remembering to keep in mind the boat would have forward momentum in that state akin to slipage on a traditional prop. They went on to recommend sizing the dia and paddle spacing so that when the downward most blade was at 90 degrees to the water, one blade would be entering the water and one would be exiting.

    If I understand your approach correctly, you are almost describing a tank tread or snow mobile type belt right? Keep in mind I will be building this boat in my home shop...has to be something I can actually build =)

    Geno
     
  11. sigurd
    Joined: Jun 2004
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    sigurd Pompuous Pangolin

    Wouldn't an alternative shallow draft propulsion be a vertically flapping wing?
    There is something called "pump-a-bike" or something using a wide, short foil as the means of both propulsion and main weight carrier. The rider is hopping up and down on the bike which oscillates the wing. Probably it would be possible to connect it to pedals instead.
     
  12. BG_Geno
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    BG_Geno Senior Member

    The hydrofoils your talking about are a facinating project in and of themselves, but not practical for this project for a few reasons. Draft being one. The wing may "fly" at only a foot of depth, but at anything less than flying speed and the boat transittions back to it's primary hull/flotation which means the wing is then running at say a two foot depth--this doesnt include the prop diameter either which still needs to be submerged when the wing is in flight. (though you do mention a flapping method rather than a propeller). Secondly is the power output required from the rider/s makes all but short distance travel difficult. Not the kind of sustained effort you would could muster for a day of use.

    Geno
     
  13. sigurd
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    sigurd Pompuous Pangolin

    I didn't mean that you should fly on foils. Only to use a horizontal, vertically oscillating foil as the means for propuulsion.
     
  14. MLampi
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    MLampi Junior Member


  15. BG_Geno
    Joined: May 2006
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    BG_Geno Senior Member

    I like the air power as a concept but I am leaning towards a more "boat like" design and feel for this project. There are some issues with the tall stance required for air power--larger cross section makes it harder to move and navigate in windy conditions (the only kind we seem to have here) and during transportation.

    I have modified the hull design incorporating most of the input from this thread. I am still looking for more information on racing skulls though. I have also transitioned into Solid Works for my software. Working on the undercarriage or down struts? now. I would love to do them in Carbon fiber like the higher end racing bikes but there isn't a lot of information on the procedure (beyond the guy using electrical tape) so I may have to use aluminum, at least for the first boat.

    Also have added a CNC hot wire for foam so I can do the hulls up very accurately, as well as forms for the frame etc. if I do figure out Carbon Fiber.

    I also now have the shop space so it looks like construction will start this winter. I will be using a paddle wheel design I believe. Trying to work out a light weight and dependable way to vary the vanes pitch throughout the rotation to improve efficiency. Not making a lot of headway there though.
     
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