Canoe with square bottom hull vs rounded hull

Discussion in 'Hydrodynamics and Aerodynamics' started by JosephT, Feb 11, 2019.

  1. Doug Halsey
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    Doug Halsey Senior Member

    The original post specified identical profile view with no rocker. It did not say the two hulls would have the same immersed depth.
     
  2. Doug Halsey
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    Doug Halsey Senior Member


    In this situation, the optimum flat-bottomed shape (for wetted surface considerations) is actually 1/2 square, not full square. (In a similar way that the round hull is 1/2 circle.)

    For the 1/2 square case, Beam @WL = 1.41, and Wetted Surface = 2.82. So the flat-bottomed hull compares to the round one much more closely.
     
    Last edited: Feb 12, 2019
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  3. fallguy
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    fallguy Senior Member

    I am just observing.

    Just for fun...

    http://human-powered-hydrofoils.com/hydrofoils/hydrofoil-kayak-flyak/

    At some point when you want speed in a canoe; it means effort and more effort is applied.

    With greater effort, things like lift come to mind versus simple hull shape.

    I am perplexed by the square shape concept with higher wsa and chines resulting in less wave making resistance.

    I will go back to my corner.
     
  4. BlueBell
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    BlueBell Ahhhhh...

    Rick W (a former member here) did extensive research on this and ended up winning a 24-hour endurance race with his "square" hull design.
    The proof is in the pudding.

    I copied some aspects of his design and won a local race with it.
    What stood out was we carried three adults, like all the boats, but only two paddled.
    The third crew-member stood and flew the hydrofoiled, single pontoon.
    We called her the Roll Technician.
     
  5. Doug Halsey
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    Doug Halsey Senior Member

    The larger wetted-surface area of the square shape affects mainly the skin-friction portion of the drag. The wavemaking resistance is strongly affected by the beam, and since the square shape is narrower than the semicircular one, it can easily have smaller wavemaking resistance.

    Whether the sum of the skin friction + wavemaking drag is greater or less is the issue.
     
  6. Doug Lord
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    Doug Lord Flight Ready

    ====================
    Is that with a 1sq' midship section? Nevermind-I figured it out-good one , Doug!
    -----------------------------------------------
    Whups! Just checked the L/B ratio and it is much worse with the 1/2 square! 7.8/1 vs
    11/1 with the square.......
     
  7. Doug Halsey
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    Doug Halsey Senior Member

    Yes, that's why I added "(for wetted surface considerations)" to what I had originally posted.

    The 1/2 square shape would have the smallest skin- friction, but larger wavemaking than the full square. Slightly better than the round shape though.

    The optimum total might be something different still & would no doubt be speed-dependent.
     
  8. fallguy
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    fallguy Senior Member

    Got a link?
     
  9. Doug Halsey
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    Doug Halsey Senior Member

    The last Moth World Champion before the foiling era was Mark Thorpe, sailing his "Hungry Tiger" design. I couldn't find a detailed drawing of a "Hungry Tiger", but Bill Beaver's "Hungry Beaver"(shown below) is said to be very similar.

    This is the shape that had evolved after many years of trial & error.

    Granted, a Moth has to operate over a wider range of speeds than a canoe, but in view of this experience, the flat design should not be taken too lightly.
     
  10. JosephT
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    JosephT Senior Member

    I recall Rick's boats. There were flat hulls, very narrow and long with outriggers. My inquiry is for a standard canoe shape (vs. long, skinny pontoon type hull).

    [​IMG]
     
  11. BlueBell
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    BlueBell Ahhhhh...

    "Pedal Powered Boats" is the title of the thread ( I don't know how to show the link... ).
    Guest625101138 is Rick W.
     
  12. Doug Lord
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    Doug Lord Flight Ready

  13. gonzo
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    gonzo Senior Member

    The wave making resistance will vary greatly depending on how much of a circular section is submerged. Therefore, the displacement is very important to compare the different shapes.
     
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  14. Dolfiman
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    Dolfiman Senior Member

    Here attached is my tentative round/square comparison using a previous project, Tandem Canoe 18', developed with Gene-Hull VE Canoe and connected to a VPP. As it was said by many, such comparison depends of the respective proportion of the friction versus residuary drag in the total, itself depending of the Froude range considered. Here I consider a Froude around 0,25 to 0,32, so a speed of around 4 to 5 mph, usual for long distance race like Yukon 1000.
    The accuracy of the comparison is all about the one of the residuary drag, which weights about 25% to 35% of the total drag estimation in this range of Froude. I used the Delft series data and the derived parametric formulation as given in book « Principle of Yachts Design » L. Larsson and R. Eliasson, 2nd edition 2000. This adimensional formulation is a drag/displacement ratio in function of Froude, and use 4 parameters (for Froude < 0,45) : Bwl/Tc , Lw / D^(1/3) , Cp , LCB. In the application, I used it just in the range of Froude Fn 0,175 to 0,325 and with a mitigation factor of 0,7 to take into account the higher Lwl/Bwl ratio of the canoes (usually > 6) compared to the limit of use of these Delft curves (Lwl/Bwl limited to 5). I confess that that 0,7 is a feeling choose presently not calibrated with towing tank data (that I still search for canoe...), the value is an input data that the user can change to test its influence on the result. Of course, CFD Tools could give a more reliable value, although to deal with a box square hull and its local turbulence should be sensitive.

    Comparison main results at constant Lwl (5,13 m), Bwl (0,79 m) and displacement (0,200 m3). At first to note that at same Bwl, the full squared sections solution leads to a greater GM, so a greater initial stability, it is not fair for the comparison. So I change by a comparison at same GM instead of at same Bwl, which leads to a bit less Bwl (0,74 m instead of 0,79m) for the full squared sections solution. Finally, in terms of performance in these conditions :
    • the full rounded sections gives a better speed of about 6-7% / full squared sections at same GM.
    • a slightly better result is obtained with mix V rounded squared sections, + 2,5% / full rounded sections.
    Also attached is the application (with the V rounded squared best solution in place, the input data of the other solutions Round, Square, Square GM are in the Hulls storage sheet) and the User guide.
     

    Attached Files:


  15. JosephT
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    JosephT Senior Member

    Excellent analysis as always Dolphiman. All of the hulls so far, though square in general appearance, do have slightly rounded edges. I finished modeling up a perfectly flat bottom (90 degree square edge) canoe last night and ran some initial numbers on it. Not too bad. I'll optimize it the best I can to make all points absolutely square and then save the model to a new file. On the next model I'll round the lower edges like a typical canoe and compare the numbers. I suspect the rounded hull will have better numbers, but we'll see.

    Flat_Bottom_Canoe.JPG

    Design length : 20.000 ft
    Design beam : 2.757 ft
    Design draft : 0.520 ft
    Midship location : 10.000 ft
    Water density : 62.428 lbs/ft^3
    Appendage coefficient : 1.0000

    ----------------------------------------------------------------------------------

    Input variables

    Hull
    Effective waterline length : 19.897 ft
    Beam on waterline : 2.376 ft
    Draft hull : 0.520 ft
    Wetted surface area : 49.90 ft^2
    Prismatic coefficient : 0.6194
    Displacement : 0.421 tons
    Half entrance-angle of dwl : 9.694 degr
    Longitudinal center of buoyancy : 0.510
    Submerged transom area ratio : 0.0000
     
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