Corrugated bottom

Discussion in 'Boat Design' started by Steboe, Aug 21, 2008.

  1. Steboe
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    Steboe Junior Member

    What effect on the planing performance does the corrugated bottom on small aluminium boats have.

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    FAST FRED Senior Member

    The trade off is extra stiffness for more wetted surface .

    So the boat might be slower at Disp speeds and slower to get on plane for same fuel use.

  3. SamSam
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    SamSam Senior Member

    It helps to keep the hull from spinning out in turns. Without them, a smooth flat bottom will spin out and then either keep spinning or a chine will catch abruptly, stopping the spin and then usually throwing people out of the boat or into a pile in the boat.
    It can be exciting.
  4. Steboe
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    Steboe Junior Member

    Thanks for your input,I'm thinking it would create a lot of tubulence.

  5. rwatson
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    rwatson Senior Member

    I guess we dont want to confuse turbulence with drag.

    There is no reason why a smooth corrugated bottom should induce any more turbulence than any other shape in a controlled flow, but there will be increased drag due to the larger wetted area.

    Now, if you are thinking turbulence would be increased in a seaway where wave and boat action send water in uncontrolled directions unde the hull - that makes sense to me.
  6. marshmat
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    marshmat Senior Member

    Fred, Sam and rwatson all have valid points.

    If you could build a smooth-bottom small aluminum boat, it may have a bit less drag than the ones you actually see, complete with ridges and strakes. But it'd flop around like a sheet of cardboard, and would be hard to turn at speed without spinning out.

    The boundary layer under virtually any planing boat is fully turbulent, and so is very sensitive to surface roughness. Small increases in surface roughness (texture, not strakes!) translate to relatively large increases in drag. (Hence why, when you touch the bottom of a raceboat on its trailer, it is mirror smooth.) But at 15 knots with maybe three square metres in the water, the added drag of the corrugations, rivets, etc. is really not that huge.

  7. blackdaisies
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    blackdaisies Senior Member

    Just like keels do, they may make a road or rut for the boat to travel in, making it use less fuel to move it for motored boats. Have you seen the huge bulbous keels that are so long, they come before the bow of the boat does creating a trail for the boat to travel in so making easier for the back of the boat to be pulled. Does that make sense to you? If it doesn't I'll try to find urls for it.

    I don't know what else other than strength it might be for if this doesn't apply.
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