water resistance problem.

Discussion in 'All Things Boats & Boating' started by Frosty, Apr 7, 2009.

  1. Frosty

    Frosty Previous Member

    Which of the two shapes described below would offer most resistance to being pulled or pushed through the water at say 20knts

    A disc if 1 foot in Dia, three attachments equally seperated to its circumference to tie three ropes.

    A cone of 1 foot in its base, the length of the cone say 3 feet. A single attachment to the tip of the cone.

    If these two shapes were to be pulled or pushed through water would they offer the same resistance.

    Both would have the void to the rear, both would have to displace 1 round foot of water, but the cone would also have surface drag.
  2. marshmat
    Joined: Apr 2005
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    Location: Ontario

    marshmat Senior Member

    Hi Frosty,

    The drag coefficient Cd, based on projected frontal area:

    Disk, normal to flow: 1.17
    Cone, 10 degree apex, pointing into flow: 0.30
    Cone, 20 degree apex, pointing into flow: 0.40

    Where drag = 1/2 * Cd *density * velocity^2 * area

    The cone's resistance is lower, by a long shot....
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