paddleboard and kayak teardrop shape

Discussion in 'Boat Design' started by Alwaysthinking., Sep 5, 2019.

  1. Alwaysthinking.
    Joined: Sep 2019
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    Alwaysthinking. Junior Member

    Thank you. I always thought it was a speed predictor because I've seen people use it as such, in arguments, on numerous occasions. Such as, my boat is fantastic because it has such a good Froud's number. Or, boat A should be faster than boat B because boat A has a better Froud's number. I was given the wrong impression.
    Look guys. I told you, you need to wait till I've played with the CAD program for a while. I plan on doing three drafts.
    Draft one: full on airfoil shaped waterline, if that is even possible with my other constraints. Starting to think it isn't. If it isn't, I'm not that proud. I'll say I should have listened to you guys.
    Draft two: Swede form with blunt bow.
    Draft three: conventional sharp bow swede form.
    As I said a couple times already, I think most of you are envisioning something that looks very different from what I'm envisioning. I may be a *****, but I'm a creative *****. I can think outside the box.
    I had no plan on using the prismatic coefficient or Froude's number as speed predictors. I don't believe in speed predictors, which was my point. I did plan on checking the prismatic and trying to get it close to "ideal number" in the chart. I have a chart, possible in Skene's Elements of Yacht Design, but it's been several years since I've played around with boat design, so had forgotten about it. I can barely remember what I had for breakfast.
    Despite what at least one person has implied, I'm not trying to be a stubborn SOB, it's just that my instinct, which is sometimes pretty good, tells me something is being missed here. Maybe I'm arrogant in thinking I'm the one that can find it when no one else has. Or it may just take someone that doesn't like being told it can't be done.
    When I start drafting, I'll probably figure out pretty quickly if there is any chance of doing what I'd hoped. If there isn't, I'll admit it. I promise.
     
  2. Blueknarr
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    Blueknarr Senior Member

    Always thinking

    An elongated teardrop might work, but it isn't the discussion you need to have now.

    I think you need to answer a few questions before starting to tackle the shape element of the design.

    What percentage of time will it be propelled standing vs sitting?
    Do you want a paddle board that can be sat upon: or a kayak that could be stood soon?

    Why waste time designing the wrong one?
     
  3. gonzo
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    gonzo Senior Member

  4. Alwaysthinking.
    Joined: Sep 2019
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    Alwaysthinking. Junior Member

    I've been thinking about that, but I'm very early in the process. I haven't even learned how to use the design program yet. I work almost ten hours a day and I nod off every time I try and study the tutorial. I have three days off this week, so I might get a chance.
    I'm thinking I will probably be sitting most of the time and just stand up to stretch and give my butt a break.
    Here's the thing. I have three canoes already, but in the last few years I've had several surgeries, the last being open heart (to replace my aortic valve) this last November. I never really learned how to swim and now I'm just a shell of the man I used to be. I need something that will be easy for me to get back on, if I fall off. Trying to empty a canoe and crawl back in is no joke.
     
  5. Blueknarr
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    Blueknarr Senior Member

    I admire your desire to learn how to design your own craft. I only offer the following observations to assist you in avoiding a few pitfalls.

    A big reason for the lack of crossover canoe/kayak\paddle boards is their very different Center of Gravitys.

    Assuming that 80% of the weight is attributed to the paddler and their CG is at their bellybutton. The CG for a kayak can be less than 1 foot from the water. a canoe 1.5 feet and a paddle board 3 feet. As the CG gets higher these vessels typically get wider to provide adequate stability: kayak 24 inches, canoe 30-36 inches and standup boatds 40+

    Paddles are most effective with vertical strokes. The wider the swing the greater the tendency to turn rather than provide forward pulpution. As these craft get wider, the shoulder height also increases, allowing for the paddle stroke to stay nearly vertical. It is very difficult to drive a paddle board straight from a seated position.

    I understand your physical limits. I can see the ease of climbing out on the blunt nose of a paddle board vs re-entry of a swamped canoe.
    Might I suggest ad a quick cheep proof of concept. Borrowing a paddle board, strapping a milk create to it and use an extra long double ended paddle. Of it works, then you could design and build a prettier version.

    Good luck
     
  6. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    I have a canoe that won't tip over.

    It sucks to paddle.

    I use it once a year or so.

    If you can't swim; a paddleboard is a death wish.
     
  7. Waterwitch
    Joined: Oct 2012
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    Waterwitch Junior Member

    Blueknarr, I have no idea where you get your dimensions for stand up paddle boards, the beam of a very wide touring or beginner board is 32 inches or so, an advanced racing stand up board can be as narrow as 23 inches. Standing on a 40 in plus beam board you might as well be paddling the floating dock. :) Even the very burdensome sit on top fishing kayaks that are advertised as being suitable to stand up on have 33 inches beam and weigh almost 100 pounds.
     
    Last edited: Sep 10, 2019
  8. Waterwitch
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    Waterwitch Junior Member

  9. Alwaysthinking.
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    Alwaysthinking. Junior Member

    I'm not married to the hybrid concept. I might change my mind. I was leaning toward a "boat" that was a little wide for a kayak and a little narrow for a paddleboard.
    I have a very long Wenonah solo canoe that I ordered with lower seats so that I could paddle it with a kayak paddle. It is wider than a typical seakayak, but I took it to Lake Powell and didn't have any real problem. I had to make a board to cover the area over my legs or I would have been bailing constantly.
     
  10. Alwaysthinking.
    Joined: Sep 2019
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    Alwaysthinking. Junior Member

    The twelve meter connection.
    It's funny the original America's cup boats were brought up as "proof" my theory wasn't good because later America's Cup boats helped form my theory.
    12 meter boats have a lot of overhang. This helps with waterline length, when heeled. A way of getting around the rule. Some of the later designs, like KZ 5, had a rather short, vertical bow that really only contacted the water when going through waves. It was the round, forward section of the bottom that actually acted as the bow most of the time. It appeared to me that a plan view of the waterline would show a rounded entry, not pointed.
    I had a hard time finding photos that showed this definitively one way or the other.
     
  11. portacruise
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    portacruise Senior Member

    The older I get, the more significant it becomes to have a sub 50 lb lightweight, stable, self bailing, one man craft operated in sheltered Waters. So that's why this senior citizen enjoys smaller tree-lined rivers which provide shelter from winds and (if necessary) searing Sun, Plus where the shoreline is only a few feet away should there be trouble. For whatever it's worth category.
     
  12. Alwaysthinking.
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    Alwaysthinking. Junior Member

  13. gonzo
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    gonzo Senior Member

    12 Meter boats are designed to beat a rule and not for real speed. Once catamarans were allowed, the overhangs disappeared because they found a different way of beating the rule.
     
  14. Alwaysthinking.
    Joined: Sep 2019
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    Alwaysthinking. Junior Member

    But they didn't need to have a round entry to break the rule. Earlier 12 meter boats had the overhang but didn't have that round entry. They must have found out that a round entry, if angled enough, did not give a performance penalty and, in fact, was a performance advantage.
     

  15. Alwaysthinking.
    Joined: Sep 2019
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    Alwaysthinking. Junior Member

    Distribution of underwater volume. It is becoming clear to me that this is where I was/am headed.
    From above (plan) the underwater shape would be airfoil shaped. Rounded entry with maximum width forward of center.
    From the side (profile) the underwater shape would be, either, swede form. That is, maximum depth would be aft of center. or the underwater profile would start very shallow and get continuously deeper the farther back you go.
    I'm also very aware that solo canoes and kayaks allow some freedom of design over other types of boats because the position of the paddler determines how the boat trims.
    Kind all of a cheat, but that's what it's all about. Finding ways to cheat physics.
    If I ever get the new CAD program figured out or get the old one installed, I can play around with distribution of underwater volume and decide which approach is best.
     
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