Pedal Powered Boats

Discussion in 'Boat Design' started by Guest625101138, Jul 14, 2008.

  1. I57
    Joined: Feb 2008
    Posts: 172
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    Location: Melbourne, Australia

    I57 Senior Member

    Gearbox

    Glen
    I know of other people who have had similar problems with their Mitrepak gearboxes. Check out Mike Lampi's blog http://hpb-er.blogspot.com/
    he was/is using a Mitrepak gearbox.

    Ian
     
  2. Submarine Tom

    Submarine Tom Previous Member

    Glen,

    Have you already posted a pic of the prop in question?
     
  3. GMR
    Joined: Sep 2011
    Posts: 54
    Likes: 1, Points: 0, Legacy Rep: 22
    Location: Nova Scotia

    GMR Junior Member

    Not yet Tom, will do that tomorrow. I did switch to a half inch shaft and dropped from 52 to 42 teeth and back to 16 x 14 APC pattern prop. Felt much better this time ....briefly!
     
  4. Submarine Tom

    Submarine Tom Previous Member

    Ya, bummer about that failure.

    I was considering spending the big bucks on one of those.

    Interesting that Rick doesn't break his all the time.
     
  5. I57
    Joined: Feb 2008
    Posts: 172
    Likes: 6, Points: 0, Legacy Rep: 62
    Location: Melbourne, Australia

    I57 Senior Member

    Gearboxes

    The 2:1 gearboxes by their design are not as robust as a 1:1 gearbox. I'm using a TEA transmissions 2:1 gearbox to get the high gear ratio and so far is holding up ok. Then again I don't race it and the boat is light and easy to push. Another option is to use a 1:1 gearbox with a big chainring, something like a 90 tooth to get the same ratio. Other way is a standard 52 tooth chainring with 12 tooth gear at the 1:1 gearbox (1:4.3 ratio). This means a bigger prop of about 400mm dia, prop can be sized using Java prop.
    Keep at it Glen, getting these things to work and going through the trial and error is half the fun.

    Ian
     
  6. GMR
    Joined: Sep 2011
    Posts: 54
    Likes: 1, Points: 0, Legacy Rep: 22
    Location: Nova Scotia

    GMR Junior Member

    157
    I am slightly put off because I had conversations with the company head office and told them what I was going to use it for. Oh well....I have made a few sprockets for my recumbents before so I will probably just make another BIGGER one and change to 1:1 ratio. I may do the CAD and ask my pal Kevin to lay out all the holes using the CNC router table with a small center drill and go from there. The more parts I make myself the better!
    My first introduction to the new and improved pedal boats came when my brother in law was sitting on his salmon trawler in Uculet BC and a tandem kayak came into the harbour with two peddle drives. Found out later it was Greg Holloway (sp?)
    I was originally basing my gear ratio choice on the drives Greg used for the Kawak and I seem to remember that he was running at approximately 8:1. This seems now to be a bit ambitious for this boat and 6:1 is more practial. However, if I can do 4:1 and use props in the 400 mm range then I already have an assortment to try. The blog you steered me towards said that they converted the 2:1 back to 1:1 for him so I will call the company and find out. And you are right, the R+D is half the fun!
    Glen
     
  7. Submarine Tom

    Submarine Tom Previous Member

    Ian,

    I don't mean to doubt you but what makes the 1:1 more robust?

    Thanks

     
  8. GMR
    Joined: Sep 2011
    Posts: 54
    Likes: 1, Points: 0, Legacy Rep: 22
    Location: Nova Scotia

    GMR Junior Member

    A while back there was post encouraging folks to improve the quality of their video clips.....so I have uploaded several clips to my blog (gmrprojects.blogspot.com) that would fit nicely into the undesirable video folder, but that is all I have at the moment. They are from two sessions, the second of which has the frame lowered 4 or 5 inches. The on-board videos were taken with 2 people in the 200 pound range and 24 feet of wet spruce 2 x 6. The wake shots are at some unknown speed but interesting none the less. At no time during the taping was anyone pushing the boat to see how fast it would go. The gearbox broke before I got to that test....
    While I wait, the hulls are back in the basement so I can touch up the paint and apply graphics. They will have to be stripped this winter anyway but the vinyl is cheap and will give me a better idea what I like or don't like. I will also work on routing rudder lines etc.

    Glen
     
  9. Submarine Tom

    Submarine Tom Previous Member

    Good on ya Glen.
     
  10. I57
    Joined: Feb 2008
    Posts: 172
    Likes: 6, Points: 0, Legacy Rep: 62
    Location: Melbourne, Australia

    I57 Senior Member

    Tom
    What I meant by the gearboxes is a 1:1 can be smaller for the same amount of power.

    Ian
     
  11. portacruise
    Joined: Jun 2009
    Posts: 1,114
    Likes: 32, Points: 48, Legacy Rep: 218
    Location: USA

    portacruise Senior Member

    Hi, Tom:

    Don't mean to butt in, but when the ratio is not 1:1 the wear on the smaller gear would be greater, because of more rotations. There is also a larger practical size limit on the gearbox, because of the practical minimum number of teeth that can be machined on the small gear. On my broken fishing reels with gear problems, it is always the smaller gear that takes the stress and causes failure. The smaller gear will wear out, get clogged with filing pieces, loosen on its shaft, etc...

    Hope this helps.

    Porta

     
  12. Submarine Tom

    Submarine Tom Previous Member

    Makes sense.

    Thanks Porta!
     
  13. Scheny
    Joined: Feb 2012
    Posts: 72
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    Location: Vienna/Austria

    Scheny Junior Member

    Most efficient hull design

    I have used the time I could not build my boat to research the impact of laminar flow on boat hulls. For this reason I have constructed three different boats with a rectangular sideview and a planview of:
    • Parabolic hull
    • YS-900 profile hull (near parabolic with max camber more at the rear)
    • NACA 66-007 profile hull (round nose and max camber at 60% length)

    All boats had a fixed beam of 0.35m and fixed length of 5m, varying only draft to a displacement of 100kg

    Despite of having a nose as big as a house, the pressure distribution of the NACA 66 series is the best of all and the water is separated even smoother than with the best wedge bow.

    The most interesting thing was, that above 3m/s speed, they all behave the same and only between 1,5m/s and 3m/s the parabolic shape has small advantages.

    YS-900 profile:
    http://www.ae.illinois.edu/m-selig/ads/afplots/ys900.gif
    NACA 66-018 profile:
    http://www.ae.illinois.edu/m-selig/ads/afplots/naca66-018.gif

    So I went a step further and had a look at the hulls with Leo's Godzilla. It showed, that any hull is optimized to a parabolic form with elliptic cross section as expected. But even more interesting was, that the algorithm now and then found a hit looking quite similar to the both profiles I had chosen rather than optimizing them to parabolic. Then I could see, that the best form for a cross section for these profiles is nearly representing a triangle.

    Wanted to join that information with you all. Maybe this is worth discussing it.

    Have nice summerdays on the lake,
    Andreas
     

    Attached Files:

  14. Submarine Tom

    Submarine Tom Previous Member

    Great work Scheny!

    Thanks for posting.
     

  15. portacruise
    Joined: Jun 2009
    Posts: 1,114
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    Location: USA

    portacruise Senior Member

    Hi, Scheny:


    Thanks for sharing. I am also interested in the most efficient shape for the shortest LENGTH, in small, 1 person boats. Shape doesn't seem to be as critical for 1 man long boats over 7 meters, from a previous posting....

    Your most efficient picture reminds me of the shape of a falling raindrop, maybe just another reason blimps don't have YS 900 shapes... I suppose one would cut that shape in half, for the best pattern of a short displacement boat?

    Wonder if there is a way to divert a little of the propulsion energy to improve or accelerate laminar flow? Perhaps dual props on either side instead of a single?

    Porta

     
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