Pedal Boat Design

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

  1. BG_Geno
    Joined: May 2006
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    BG_Geno Senior Member

    They are just bone stock avi files. Windows media player should play them fine. If your still having problems please let me know and I will point you to the right (and by far best) codec pack.

    In fact, heres a download link. It is for the K lite codec pack which has just about every video codec you could ever need in one easy to install package. Dou yourself a favor and click the yes button for media player classic too during the install as its still better then Microsofts bloated media player 9 (and no DRM crap either)

    http://www.free-codecs.com/download/k_lite_Mega_Codec_Pack.htm
     
  2. BG_Geno
    Joined: May 2006
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    BG_Geno Senior Member

    I froze the animation right when a paddle enter the water (if your using media player classic just press play, then pause and you can use the left and right arrow keys to go frame by frame) and red lined the point where it enters.

    I did not think that is the pattern we would see just by looking at the paddle shape. I would have expected the right edge to enter the water first.

    Weird.
     

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  3. clmanges
    Joined: Jul 2008
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    clmanges Senior Member

    BG,
    I'll bet it is interesting. I wish I could see it.
    I just get a blank screen.

    At times like these, I remember what a friend of mine says from time to time . . .

    "I hate computers!"

    I blame the "plug-in of the week" syndrome. Oh well.

    Btw, why did you choose seven blades? I only picked six as an arbitrary starting point, because four clearly was too few.
     
    Last edited: Aug 22, 2008
  4. clmanges
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    clmanges Senior Member

    BG,
    Sorry, I missed your last two posts because I was looking at the wrong page.
    I have an iMac, no *******. I was going to look for that technical reader/viewer thing you linked to a while ago.

    I'll be back.

    Oh, and the red-line on your still shot -- go back to my last drawing and you'll see that the corner you marked is indeed the one closest to the water line.
    This thing tends to throw your expectations around, and it's going to be very interesting to find out how it behaves in real water. For one thing, due to the fact that the inboard and outboard sides have different diameters, the inboard and outboard edges of the floats are actually moving at different speeds. That is, they both turn at the same RPM, of course, but have differing circumferences. I think stuff like that is going to make it hard to run calculations for, but I don't really know.
     
  5. clmanges
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    clmanges Senior Member

    Oh, am, this is amazing -- and creepy -- when I typed this line
    I actually typed in "*******" and my computer censored it! Let's see if it happens again --
     
  6. clmanges
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    clmanges Senior Member

    . . . or maybe the board's server censored it -- it was a corruption (not obscene or profane) of "windows."

    Anyway, K-lite won't help me either. Just send still screen-shots or something.

    Curtis
     
    Last edited: Aug 22, 2008
  7. BG_Geno
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    BG_Geno Senior Member

    Let me see if I can save it as a quick time.
     
  8. BG_Geno
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    BG_Geno Senior Member

    Nope...no Quick Time option, but I checked and the player at this link works on Mac and plays .avi and Xvid files.

    http://www.videolan.org/

    I googled "play .avi files on a Mac" and there are a bunch of free players if you don't like that one.

    How can you function without being able to watch avi and Xvid files? I download all my shows and movies now and skip the commercials =)
     
  9. BG_Geno
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    BG_Geno Senior Member

    Watching the animation...It might just be me (Rick will know better) but it sure looks like your actually going to be pumping water towards the side of the boat almost like a "river pump".
     
  10. clmanges
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    clmanges Senior Member

    I've already got the videolan player, and it doesn't work either with these clips, though it will play some stuff for me that others won't. I'll have a look at the source code for your clip and see if I can get any hints. Plug-ins are a nightmare, though.
    I'm certain of that; this thing is going to be centrifuging water outwards (well, inwards, in this case) and down (that part you'd expect from any wheel), since the blades move in an arc relative to the surface. I figure the hull will redirect the flow in the desired direction. This makes me wonder also about how that flow will be directed beneath the hull, and whether that will help or not. Ordinary boat oars move in a similar arc and it doesn't seem to hurt them. Rick (or someone else here) might have something interesting to say about it

    This is certainly a popular topic, for whatever reason, you see how many views this thread is getting?

    Curtis
     
  11. Guest625101138

    Guest625101138 Previous Member

    Large diameter, wide wheels do the best. Everything else is a compromise that costs energy.

    Compare your oars with those on a rowing scull. It is no accident that they go to the trouble of using long shafts with large blades. They are carbon fibre to get strength, stiffness and low weight. There are a pair of oars priced here:
    http://pacificrowing.com/pricing2008.pdf

    Also take a look at kayak paddles. Their size relative to the hull they are pushing and the technique of a good paddler. Here is price of a good paddle:
    http://www.roscocanoes.com.au/accessorydescription.aspx?sec_ID=371&fulID=199#1

    These high efficiency arrangements get high 60 to low 70% efficiency. The oars in a rowing dinghy are likely to be well under 50% but it does not matter much because the boat will not go very fast so more effort just goes into bigger waves.

    Rick W
     
  12. Guest625101138

    Guest625101138 Previous Member

    I should add that an efficient paddle wheel must have low slip. So the blades are not moving through the water very fast. If the boat is doing 3m/s then the blades should only be doing say 0.3m/s relative to the water. This means if there is a large variation in radius of the section of the paddle in the water you could actually have part of the blade acting as a brake.

    This is why I limit immersion for unfeathered blades to 60 degrees of arc and use quite shallow blades. AS you go up with immersion angle you get reduced forward component of the velocity vector as the blade enters the water so this part is not doing anything anyhow. Similarly on the exit you are getting reduced velocity of the blade in the direction of travel as there is an increasing vertical component.

    What seems simple is not all that simple when you get down to analysing what is actually going on.
     
  13. BG_Geno
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    BG_Geno Senior Member

    Sigh. I hate to ask Rick, but what do you mean by 60 degrees of arc?

    I am designing the drive train now and OH MY are there a ton of choices for chain rings and cranks etc. I saw a BMX bike front chain ring with 43 teeth for $500...just for the chain ring. WoW! People are nuts lol.

    So. If we look at a wheel diameter of 36" (.9144m) and a width of 14" (.3556m) with 12 paddles and either 4" (.1016m) or 6" (.1524m) paddle depth, (with well designed paddles for streamlined entry/exit) we get a per paddle area of 56 sq in (.03613m) or 84 sq in (.05419m) respectively. I know you don't like that 14" (.3556m) width Rick but there will actually be two of them so we get 28" (.7112m) of total width. Keep in mind that each engine runs only one though.

    What size chain rings front and back would you suggest to get the 70 rpm you targeted for the engine?

    Plucking numbers out of a jumbled paragraph sucks so I am attaching a spread sheet Rick.

    If it helps, I can also get the maximum area of the paddle/s that would be submerged at one time. I think that as this number is fixed regardless of where you are at in the rotation that it is a valid data set for us to track.

    Did you happen to see the Kayak gold medalist after his run? He was rather elated and to celebrate he just smashed his paddle over the top of his boat, like you would a stick over your knee. Not CF obviously lol
     

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  14. clmanges
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    clmanges Senior Member

    Sixty degrees of arc on my latest design yields an immersion depth of about an inch and a half . . .

    . . . grr-r-r . . .

    BG, if you could post a still of the underwater view of my wheel, I'd like to see that.

    Rick, here's a plumb flaky idea, but just for entertainment purposes -- what would happen to a normal paddle wheel if the flat-plate floats were replaced with cylinders of the same diameter as the float width?
     

  15. Guest625101138

    Guest625101138 Previous Member

    Immersion angle - If you place a radial line from the point where the blade enters the water and another line to the point where it exits then I recommend the angle between the two lines be no more than 60 degrees. The efficiency goes down as the angle is increased.

    Cadence - A comfortable cadence is around 60rpm. Aggressive cadence for the untrained is 75rpm. A wheel around the 1m mark can be driven at cadence. I suggested earlier that you consider crank rods rather than chains. If you have a common pedal shaft and two crank rods at 90 degrees you have a nice simple drive system that avoids chains. The best arrangement for two pedallers is to have the foot pedals phased at 90 as well so one rider helps the other through the dead spot. It means nice smooth action. From what I have seen the old paddle steamers used crank rods not chains. A single wheel means only two support points so you can get more blade width.
     
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