2 person Human powered boat

Discussion in 'Props' started by r3_alaska, Jun 8, 2014.

  1. r3_alaska
    Joined: Jun 2014
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    Location: Alaska

    r3_alaska New Member

    I am building a two person Human powered boat. I was wondering if the
    boat would be faster if each person drives one 16x16 prop or if I combine both riders to drive a single prop with a greater pitch?
     
  2. Petros
    Joined: Oct 2007
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    Location: Arlington, WA-USA

    Petros Senior Member

    one larger prop will be much more efficient than two smaller ones. You would also have less parts to make, and less to malfunction as well.

    Also, if one person stopped pedaling for a break or to scratch his knee, there would be no drag increase from one of two props stopping, the would just the one prop in the water, powered by one crew rather than two.

    The larger diameter (and slower turning) the prop, the more efficient it will be. less drag, less friction, less root interference as a percent of the total, etc.
     
  3. r3_alaska
    Joined: Jun 2014
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    r3_alaska New Member

    Petros - Thanks for the fast reply

    The last 3 years daughter and I won our local 2 man race each turning a 16x14 hobby prop. This year the competition is stepping up their designs. So let me see if I got this right. Lets say we work together and turn a single 20x18 or 20x22 hobby prop do you think we will increase our speed over the two 16x14's all things being equal. If not what recommendations do you have.
     
  4. kroberts
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    kroberts Senior Member

  5. Petros
    Joined: Oct 2007
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    Location: Arlington, WA-USA

    Petros Senior Member

    matching the prop to the power output takes specialized knowlage for your very low output number. it is a matter of matching blade swept area, pitch at the particularl rpm.

    you will need to take to a specialist for that.
     
  6. jehardiman
    Joined: Aug 2004
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    jehardiman Senior Member

    While it is true that you will spend 90% of the time and money trying to get the last 10% out of the prop, it is suprizing how good a piece of flat plate bent with a cresent wrench can be when the diameter and aspect ratio are good.
     
  7. kroberts
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    kroberts Senior Member

    The guy I linked to above has been doing this for quite awhile. He has record-holding boats. He sells a prop. You might want to send him an email. Also google 'Rick Willoughby' and you get youtube and other interesting links.

    Or, search for him here on the forum. There are 14 pages of hits.
     
  8. Petros
    Joined: Oct 2007
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    Petros Senior Member

    If you find a good off the self prop for a human powered boat, let us know where you found it. I have been wanting to build a human powered kayak-like boat like Rick Willoughby has and have been wondering if I could buy such a prop, rather than have to make it myself.
     

  9. fusioneng
    Joined: Apr 2013
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    Location: sarasota,fl

    fusioneng Junior Member

    I'm just curious, have you looked at the Hobie Mirage pedal drive system, I have a 2 person pedal boat (Hobie Tandem Island) using the Hobie pedal drive system and it does everything I need it to do, I feel the mirage system which works similar to penguin flippers with a back and forth motion is more efficient and consumes less energy than any propeller drive I have seen, used, or heard of. But then again that's just my opinion.
    I take my pedal boat every weekend and pedal minimum 15 miles every week as part of my exercise program, and have done quite a few 50-60 milers on weekends. I live in South Florida (and the Keys), so I am able to go out all year round.
    I'm just curious
    Bob
     
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