Fast Stand Up Paddle board design?

Discussion in 'Hydrodynamics and Aerodynamics' started by Adam B, Oct 9, 2012.

  1. Adam B
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    Adam B Junior Member

    I'm working on a second prototype of an inflatable Stand Up Paddle board for (fast) paddling on rather flat water. Now I'm wondering what is the fastest shape for the SUP?

    the board is 12'6'' or 381 cm long, 30'' or 78 cm wide, the paddler stand on the centre point and the speed varies between 7 - 14 km/h max. The material inflatable is quite stiff, the bottom has to be flat (due material reasons) and the rail on the tail is quite square/90 degrees

    Just like sailing yachts, I put the widest point more to the tail of the board, and looking to the sketch of the board, what can be improved?


    [​IMG]
     
  2. Petros
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    Petros Senior Member

    The fastest design would be long and narrow with a semicircle bottom (cross section). It would have the lowest drag and the lowest wetted surface area.

    But this would be almost impossible to stand up on and stay on. So you have a fundamental conflict with "fast" and "paddle board". A conventional sea kayak would be faster.

    If you are making it inflatable you might consider a catamaran design, two long thin tubes, it will give you stablity and lower wetted area than a conventional paddle board shape. adding length will make it more stable without the conventional width, the more width you have the more drag it will create, but of course too narrow would be difficult to balance on it, making it longer would help this stablity.

    paddles boards are not the most efficient way to get around on water, I think they were invented as a fun way to exercise, not for speed.
     
  3. Doug Lord
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    Doug Lord Flight Ready

  4. Adam B
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    Adam B Junior Member

    Yes I know a kayak is faster and more efficient etc. , but I just like stand up paddling, also because it can catch a wave (and therefore a catamaran shape doesn't suit because it doesn't surf).

    For the bottom, it has to be flat due the material of which inflatable boards are made, (over the whole length it is 4 inch thick).

    Within those boudaries I'm very interested in what the best shape is for a (mono hull) inflatable board:
    -> Is it better to put the widest point more towards the tail?
    -> What is the best tail shape to create the least drag?
    -> Does the rocker in the tail also reduce the drag?
     
  5. Submarine Tom

    Submarine Tom Previous Member

    If it's speed you're after then a cat IS your best choice.

    They can surf just fine too.

    Otherwise, what's the point?

    And if they're inflatable, dimensions shouldn't hold you back.

    20' X 6" times two should do it.

    You may want to consider a platform about the dimensions of a standard board (but much thinner) with the pontoons at the outer edge.

    Sounds like a fun project but I still can't quite understand why...
     
  6. tspeer
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    tspeer Senior Member

    I wonder if a catamaran hull form would be a better choice for a standup paddle craft.

    Since a single-bladed paddle is used, I've also wondered about the efficiency of switching from side to side vs paddling on one side using a J stroke. Which in turn leads to wondering if the hull should be asymmetrical, ala a Venetian gondola.
     
  7. Petros
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    Petros Senior Member

    catamarns surf fine, what makes you think they do not?

    If you are going to stick with a wide draggy flat board shape, than put the widest point near the center, pointy stern, no rocker. The largest length to beam ratio you can handle (long and skinny rather than short and fat) would also be best.
     
  8. Adam B
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    Adam B Junior Member

    I Think catamarans are to wide to surf, they cannot turn on a wave like a surfboard so therefore the SUP has to be a monohull/a board of one piece
     
  9. Adam B
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    Adam B Junior Member

    another question is why do most modern sail yachts have their widest point behind their centre point and also they often have a square tail.
    Is this design also suitable for SUP's because more or lees they sail with the same speed.
     
  10. messabout
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    messabout Senior Member

    No not suitable for the SUP. When the widest point is aft of the center it is called swedeform, when forward of center it is fishform. Your paddle board will be better served for all round use if it has it's widest point at the center. If you want to be really technical about it, some of our most eminently qualified members say that the plan view curve (the curve of the sides) should have the parabolic form.

    No!, do not square off the aft end. To do so will create serious drag. And no I do not think that sailing yachts sail at the same speed as a paddleboard. They sail much faster than the PB. About the best you can hope for with a 12 foot boat is about 4 MPH unless you are surfing. Since your boat will be an inflateable, the rigidity or absence of rigidity will diminish the usefulness of technical machinations.
     
  11. Adam B
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    Adam B Junior Member

    thanx for the info about swede and fish form.

    Does a square tail with rocker also create much drag, much more than a pintail e.g.? Because most of the race SUP boards have a square tail (maybe also because of balance reasons).

    Paddle boards reache a speed of 4 to 8 mph or 6-7 to 14km, or at least, a friend claimed more then 13 km/h but I'm unsure because the hull speed of a 12 foot board can only be 5 knts.
     
  12. Submarine Tom

    Submarine Tom Previous Member

    Under paddle, 4 knots tops for a SUP.
     
  13. Leo Lazauskas
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    Leo Lazauskas Senior Member

    Some of them were probably talking about pure displacement vessels ;)

    There is a sharp peak in the wave resistance of planing vessels, and it is not
    always easy to get past this hump.
    One way, common to skillful surfers and waterskiiers, is to shift the centre of
    gravity forward temporarily.
    Therefore, a fore-aft symmetric hull might not be the best for this situation.
     
  14. Leo Lazauskas
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    Leo Lazauskas Senior Member

    Forget about hull speed. It is a fairly useless concept.

    Here is a short simple paper you might like to read:
    http://www.hydrocompinc.com/knowledge/whitepapers/HC139-HullSpeed.pdf
     
    Last edited: Oct 12, 2012

  15. Adam B
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    Adam B Junior Member

    I studied most of the race sups and lot of them have a square tail, rocker in it and a little rocker/scoop in the front. Almost all the 12.6 boards are 28 inch wide but the place of the widest point varies.
     
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