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Re: [bolger] Re: does water flow around or under boat hulls?

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  • Bruce Hallman
    ... It s relative of course. Being massive, the water stays more or less still. It moves briefly out of the way, and then returns to position, as the hull
    Message 1 of 21 , Jan 3, 2011
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      > water flows under the hull, not around the hull.

      It's relative of course. Being massive, the water stays more or less still.

      It moves briefly out of the way, and then returns to position, as the
      hull passes through the water.
    • c.ruzer
      On the other hand if upright and deep bellied, then Bernouli will see the water flow under to the region of higher speed, lower pressure. Therefore note how,
      Message 2 of 21 , Jan 4, 2011
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        On the other hand if upright and deep bellied, then Bernouli will see the water flow under to the region of higher speed, lower pressure. Therefore note how, for even the light displacement flat-bottomed, sharp-bowed, chined boats eg from CWS through Cj and JB to Jinni, double-ended, flared or plumb sided, in the bodyplan the chine line bisects the angle between bottom and topsides from somewhere around midships, and sometimes thence all the way aft. This is the section of most/all of the swelling displacement in proper trim (as someone earlier noted PCB typically placed COB approx 60% aft...) and so has relatively higher water flow speeds. In proper trim the low bows of these boats are just above the load waterline but gain much clearance with heeling. Nevertheless the boats float/sail mostly on those immersed equally curved sections much further aft. Bernouli still sucks there, but more equally, so helping to minimise cross chine flow. The features are apparent in numerous boats drawn by PCB's mentor, Chapelle. If trimmed bow down, cross chine flow near their flat, sharp bow creates high drag eddies underneath which not only slow, but have the moment to turn the boat and induce added high drag from the compensating rudder. The cross chine flow induced drag at such a bow is much worse in waves as the verticle movement increases the relatve water flow speed amplifying the issue. PCB likened such a bow, any immersed narrow bow, to sailing a wineglass sterned boat flat-out backwards.





        --- In bolger@yahoogroups.com, "Peter" <pvanderwaart@...> wrote:
        >
        >
        > > I think Phil realized water flows under the hull.
        >
        > Yes. In the discussion quoted, he is only interested in the flow over the chines. Of course, it's great if the water is neatly divided by the chine, but that can't be arranged all the time. In his view, it was important that the flow be from under the boat to the side as much as possible.
        >
        > Water being incompressible, it's pretty clear that water is going to be pushed to the side, somehow, somewhere.
        >
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