Pedal Boat Design

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

  1. BG_Geno
    Joined: May 2006
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    Location: South Texas

    BG_Geno Senior Member

    Rick--

    When I rotate the wheel to the point where a given paddle goes beyond 180 degrees (the point where a paddle could be considered to be carrying water) the "holding area" for want of a better word (think cup or bowl) is pretty small. With a hole in the rim there, and it would be a fair sized hole, I just don't feel like the exterior of the wheel--call it the paddle side of the rim--has much water lifting capacity.

    If your referring to the interior of the wheel...well, theres not exactly a lot of lifting surfaces in there and gravity is going to do what it always does.

    I agree 100% on an optimal blade angle, but so far every one that looks good on the downward portion of the rotation looks as bad on the upward portion. Honestly, I think you nailed the BIGGEST contributing factor when you promoted bigger diameter, shorter paddles, and 60 degrees. All that said, if you (or any of the other guys) can track us down some sort of force measuring springs I would be happy to build a paddle wheel test bench/tank with a frictionless sled for mounting wheels in a tank with a set RPM and a clear side so we can measure the amount of pull a certain wheel can deliver and SEE whats happening.

    Props.

    If you will cross the pond and kill off all the weeds and dredge out a few thousand square klicks of the Inter Coastal Waterway I would be more then happy to use a prop =) Kidding aside, its like carpet for a good deal of the year here. I have never lost a fishing bobber or hook, but it clogs props like mad. As for depth, I have been sitting on the deck of Parrot Eyes (cleverly named pub here on South Padre Island, facing the bay side) and watched coyotes downing cranes 500 feet from the shore line--it's THAT shallow lol.

    Paddle wheel physics. I know my mathematical ineptitude must make you cringe. I REALLY appreciate your patience and as I said earlier, I am willing to build a tank mounted test sled and gather all the numbers you could ever want and freely share them with our community.

    The two wheels thing. Honestly, the math is beyond me. In my rather narrow view it looks like this. 2 engines on a wheel 28" wide make xxx thrust at the water line. Split the wheel in half and let each engine run one half...you still have 2 engines running 28" of wheel width. In fact I might argue that the odds of both engines performing at the same peak level is never likely to happen, and rather then the faster/stronger engine speeding up the slower one, the reverse will happen. Why not let the better engine develop its full potential? Yes I did read what you said about loco style cranks and the counter balancing effects, but crank style arms are not a good option for me. Why do hot cars have posi-traction rear ends? (lame example I know)

    The big difference for me is that if one engine wants to stop pedaling or slow down to take a picture or pet the dog I don't get a pedal in my shin. It's about usability in this case (for me). If it costs me 1 mph in speed it is worth it. Sounds like being a sissy, but if I clobbered my wife in the shin I would feel pretty bad. I don't doubt for a second that it's less efficient and the math will back it up, but usability is important too, and usability is measured in smiles, not math (unless math makes you smile =)

    Anyway, just wanted to say again I thank you for your patience and generosity with your time. All of you guys in fact...except the drunken LP guy =)
     
  2. clmanges
    Joined: Jul 2008
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    clmanges Senior Member

    Sure, but they're even better with castle nuts!
     
  3. BG_Geno
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    BG_Geno Senior Member

    Measured at where? Does that mean the paddle wheel sprocket needs to have 1.3 times the diameter of the pedal crank sprocket?
     
  4. BG_Geno
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    BG_Geno Senior Member

    I didn't even have to look that one up...is THAT what those are called? Apt name =)
     
  5. BG_Geno
    Joined: May 2006
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    BG_Geno Senior Member

    Curtis--

    Don't spokes have to have an off set though? I think the minimum is like 3" for street type bikes that get low lateral loads. BMX and mountain bikes have even wider off sets. You would have to do them on both sides too. Would have to be stainless spokes and hardware I suspect too as most aluminum would stretch, though I don't know for sure. Based on Ricks video of his flexible shaft prop, there are probably pretty decent lateral/side loads too.

    I am still not clear on how you tie the two "bicycle rims" together either because if you have the drive sprocket on only one side that loaded rim is going to want to twist on the unloaded one. From my airplane days I know wire bracing is worthless for radial or cross torsional loading.

    Also Curtis, if you had a PC and not a Mac I could hook you up with Solid Works. One of the few perks of running a PC modding and review site =)

    Food for thought. I will tinker with it.
     
  6. alexlebrit
    Joined: Aug 2006
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    Location: France - Bourbriac

    alexlebrit Senior Member

    Buoyant Paddlewheels?

    Not wanting to draw the thread any further away, but, what about buoyant paddlewheels? I'm not taliking about this

    [​IMG]

    type of amphibious thing which seem to flounder round various beach resorts, but instead something designed solely for water use. I'm thinking a series of pedal-powered drums acting as paddle wheels and providing the sole means of flotation. The only thing is my maths is well below par when it comes to working out how much flotation you'd need what diameter drums and how many etc.

    Would it work at all?
     
  7. Guest625101138

    Guest625101138 Previous Member

    Similar to the one shown - POORLY.

    It has three very poorly shaped hulls. They are exact opposite of the long slender hulls that are required for low wave making. Adding more very inefficient hulls just makes it worse.

    Rick W.
     
  8. Guest625101138

    Guest625101138 Previous Member

    BG
    I found this old layout of a recumbent drive set up. This was for gearboxes and I am not sure about the heel clearance to the gearbox shaft but this is not an issue for you. What is does show is the sort of separation required for in-line recumbent riders. They require a lot of length.
     

    Attached Files:

  9. alexlebrit
    Joined: Aug 2006
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    alexlebrit Senior Member

    Out of interest Rick, why? Does it make no difference at all if your hulls are rolling at your water speed? Admittedly I have no knowledge of these things at all, but I can't help but feel that rolling along is better than pushing through. But that's just me.
     
  10. Guest625101138

    Guest625101138 Previous Member

    Alex
    By allowing the hull to roll you only reduce viscous drag. A short hull has a low hull speed and the low length to beam ratio means wave drag will be substantial. So the main component of drag, wave drag, is still present. The rolling wheels still have to carve a trench through the water.

    Think about riding a bike through sand. The wheel sinks in and you leave a trench. Really it does not make much difference if the wheel turns or not, the drag is still very high.

    AND before you make the next logical brainstorm by using long slender buoyant tracks. It has been thought about but seems very difficult to engineer. In theory it could reduce viscous drag substantially. In fact use it to advantege to propel the boat.

    Rick W
     
  11. alexlebrit
    Joined: Aug 2006
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    Location: France - Bourbriac

    alexlebrit Senior Member

    Right, that does being to make sense now Rick, thank you.
     
  12. Village_Idiot
    Joined: Oct 2007
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    Village_Idiot Senior Member

    I realize they aren't feathered, which is why I put the term in quotes. I was merely looking at a way of reducing resistance of the paddle when it was not perfectly vertical. If you can't do that by angling the blades, then perhaps you could do it by reducing the surface area of the blade. Just a different way of achieving the same end result.
     
  13. Village_Idiot
    Joined: Oct 2007
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    Village_Idiot Senior Member

    Hence my earlier comment on the advantage of using twin counter-rotating paddlewheels if you are going the angled route...
     
  14. clmanges
    Joined: Jul 2008
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    Location: Ohio

    clmanges Senior Member

    Not sure what you mean by offset, but the spokes are arranged to pull on the rim from alternate sides of the hub. Is that it? Also, the spokes need to be laced in a cross pattern to carry the driving torque; there are more than one lacing pattern, called two-cross, three-cross, etc., and argument about which is best. Here are some references:

    http://www.dogpile.com/dogpile/ws/r...e/iq=true/zoom=off/_iceUrlFlag=7?_IceUrl=true

    I'm not sure that you'd need to follow all the same protocols for your paddle wheel as are needed for a bike wheel; you might get away with one set of spokes per end.

    I have to admit that I completely failed to consider the driving torque wanting to twist the whole paddlewheel assembly. The tubular center shaft would take up some of that, and I don't know how much of the rest would be handled by the floats. Now, I tend to agree with Rick, that you should have a single paddlewheel, and in that case, you could have drive sprockets at both ends of the wheel, reducing the torque.

    As to lateral loading, I have no idea, but I don't think you can logically compare the paddle wheel to Rick's prop shaft, they would experience lateral forces in completely different ways.

    I have a question: are you able to incorporate metal parts into your CF fabrications? I thought it would be helpful if you could, to combine material properties where needed.
     

  15. clmanges
    Joined: Jul 2008
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    Location: Ohio

    clmanges Senior Member

    V. I.,
    I'm not sure what you mean by this . . . clarify?
     
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