Hydrodynamics vs wetted area in scows

Discussion in 'Boat Design' started by misanthropicexplore, Apr 13, 2018.

  1. misanthropicexplore
    Joined: Apr 2018
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    Location: Upper middle Missouri River

    misanthropicexplore Junior Member

    Practicality aside and ignoring sails or propeller torque changes to roll axis, which takes more energy per knot?

    A 5x10 scow
    A 2x25 scow
    Or 2 x 29 double ended boat

    All three have the same displacement and wetted area.
     
  2. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    At what speed range, and what are the approximate shapes?
     
  3. misanthropicexplore
    Joined: Apr 2018
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    Location: Upper middle Missouri River

    misanthropicexplore Junior Member

    All have little to very mild rocker, with a boxy transverse profile, and hard chines, so a Bolger Box to dory sort of shape.
    The 5x10 and 2 x 25 would be rectilinear barge type hulls, where the bow transom is nearly as wide as the midships and just sort of rolls up.
    The 2 x 29 would be like a Wharram catamaran with a dory hull.
    I think the max hull speed for a 10' barge type hull is about 3.5 knots, so let's use that as the intended speed for all three, and we'll say we are on flat inland water.
     
  4. Yellowjacket
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    Yellowjacket Senior Member

    At that low a speed it won't matter much between the two skinny hulls, but the longer skinny hull would have the lower drag at that low speed.... Keeping the speed well below hull speed means that the wave making drag is low for the two long hulls, where it is getting more significant for the short hull.

    Scow's are planing hulls and are designed to get up on a plane. For any planing hull there is an optimum location of the CG and propulsion moments (sail or motor) that provides the highest speed. That is, the minimum drag speed for any configuration changes with the CG location and propulsion moments. If you have a heavy hull with an aft cg and aren't going very fast you want a wide hull to plane that efficiently. If you have a CG further forward you want a narrower hull, so that is why Gnozo asked for the speed range.
     

  5. misanthropicexplore
    Joined: Apr 2018
    Posts: 54
    Likes: 2, Points: 8
    Location: Upper middle Missouri River

    misanthropicexplore Junior Member

    I'm fascinated by low speed, low energy, high prismatic coefficient, hull designs, and I'm always trying to understand what makes barges move so much for so little energy per ton, so I meant more like displacement barges than planning scows. Thank you both.
     
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