paddleboard and kayak teardrop shape

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

  1. DCockey
    Joined: Oct 2009
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    DCockey Senior Member

    Is this based on your own observations or something you read?
     
  2. Ilan Voyager
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    Ilan Voyager Senior Member

    Boats moved by oars and similars beneficiate of a few thousands years old experience. Millions have been built from 4 feet round tubs to 100 and more feet warships. Hundreds of traditional rowing and paddle boats are documented. Hundreds of sport rowing and paddle boats have been designed.
    That means that any imaginable shape in all its minute details has been experimented. The successful ones has been refined to the extreme sometimes with lots of science, test tanks, hydrodynamic computing, influence of the movements of the crew while rowing or paddling. The theory and the maths are known by the specialists.
    So except inventing low speed foils there is little place for innovation.
     
  3. Waterwitch
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    Waterwitch Junior Member

    7 pages already, there is a phenomenon on this forum for the more improbable the design the longer the thread: with some exceptions like the fast row boat thread. There is still room for innovation in paddleboards and canoes in that the foam cored, carbon fiber skinned, sit on top , self bailing venturi cockpit, rudder steered canoes and paddle boards did not exist until recently. The Tahitian paddling style which defies conventional thinking about paddling ergonomics on ocean canoes and paddleboards proves to be the fastest. The Swede form of kayak with the max beam aft was designed for an easy forward stroke ,with paddle clearance along the hull, while giving stability with wide beam aft can prove to be a faster boat being more ergonomic, for what ever minute hydrodynamic advantage might be gained otherwise.
     
  4. DCockey
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    DCockey Senior Member

    My understanding is the shape of some canoes and/or kayaks with maximum beam aft of the paddler was due to rules requiring a minimum beam, not for hydrodynamic considerations.
     
  5. sharpii2
    Joined: May 2004
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    sharpii2 Senior Member

    It is based on observations I have made through reading. I don't claim to be an expert, but I do have a number of books in my library which show an admittingly small number of European work boats from the age of sail. the majority of them have the max Beam forward of their mid-length.
     
  6. Waterwitch
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    Waterwitch Junior Member

    Yes marathon canoes with their diamond shaped deck plans are made to conform to minimum beam requirements but then taper to needle points on both ends. Swede form touring kayaks for which there are no class rules are shaped for better paddle clearance.
     
  7. Magnus W
    Joined: Nov 2017
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    Location: Sweden

    Magnus W Senior Member

    I served on a sibling to the Collins, the Swedish Västergötland-class (now upgraded with aip and called the Södermanland-class).
    We had a surface mass of circa 1070 metric tonnes and 1100 submerged, so about three percent. This iirc was low by comparison.
    No sub has much reserve bouyancy, oerhaps 10 percent is normal. And why would they? Waste of hull volume and time consuming when diving.
    Most of what you see on the Collins is indeed superstructure and it’s water filled when submerged. In the Västergötland case, we had a surface draft of 6 meters and the pressure hull diameter was 6,1. Since basically no keel it means the only the top of the pressure hull was above water when surfaced.
    FWIW.
     

  8. Kenneth Dodd
    Joined: Sep 2019
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    Location: Texas

    Kenneth Dodd Junior Member

    I have some experience in this area and am currently designing a build facing somewhat of the same problem. I race canoes and I can tell you from experience of having seen these things in action as well as races them, that sharp asymmetrical hull shapes are the norm. Our canoes have very long tapered , pointed bows and the max width in beam falls behind the actual centerline. This has more to do with drag and "cutting" the water as opposed to pushing. That being said, these boat do not track! We use rudders to actually track straight. It is false when people think that when you turn you're pulling the bow when you're really swinging the stern. The bow is almost at a pivot. So our bows have very little to no rocket in them and the stern of the boat will have a moderate amount to allow the swing to be more efficient. Mind you my build will be 37 feet long, front steerage is a must and is more often accomplished by our now man who pulls the bow with draw strokes. This and a combination of leaning the boat to change the shape of the hull in the water help to turn faster, get off the rudder and regain scrubbed off speed as soon as possible. There is always a trade off. If you want to turn its gonna drag, if you want to reduce drag, you have to find other ways to turn
     
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