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50622Re: External chines (runners?)

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  • graeme19121984
    Sep 1, 2006
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      Hi David,

      the small sharpie designs of Matt Leyden have done well in his
      hands, especially in competition. There is a high degee of interest
      in the chine runners of his later designs, and much speculation as
      to how they may or may not work to affect the performance of flat
      bottomed sailing boats. I predict zillions of his Enigma design will
      be built if he makes them available. Quite a few people are
      pondering on the effect(s) of chine logs, and more on the possibly
      derived chine-runners. Among many interesting theories are that they
      may reduce turbulence, perhaps by an end-plate effect, or by
      turbulence suppressing and lift generating chine anti-vortexes.
      AFAIK PCB is mute on this point.


      PCB mentions a number of the chine effects on sailing sharpies under
      way, but as far as I know never has said they generate lift to
      windward, or signifcantly reduce leeway. Apart from the detrimental
      effects of the sharpie chine (especially at the bow) positives
      include: an increase in water line length when heeled, with
      commensurate increase in waterline L/B; and reduction in pounding
      and resistance when heeled (but he also notes that sharpies should
      be sailed flat?). There may be more.

      In considering the Light Dory Type V rowboat external chine log
      effects PCB does not touch on any that may be possibly of interest
      to the consideration of sailing hull performance other than to
      comment on two things: a minute increase of stability; and that he
      thinks they cause no increase in resistance (being effectively
      neutral). He is mute as to their effect on turbulence. He observes
      at various times that the means of reducing the phenomenon of
      sharpie chine vortex turbulence is to have equal curvature of the
      chine line in profile and plan views. AFAIK he doesn't consider
      external chine logs in this regard specifically, but an indicator
      may be that of the sailing sharpies he has designed to conform to
      this theory very few have such chine logs. Even there I'm not so
      sure those designs such as Black Skimmer, and Flying Schooner, fully
      conform to the theory at the bow when under way.

      An English "Brick" sailor recently posted to the micro-cruising
      group that he noted better windward performance the more he heeled
      the boat by shifting his weight to the lee side. He noted that the
      heeled immersed shape reminded him of a type of wing section used on
      rubber band powered model planes. Many proa authorities think
      certain types of pacific proa gain lift to windward from a similar,
      if stretched, immersed shape. There is an old September 98 MAIB
      article, "Dreamboats", that also may give some pointers as to how a
      flat bottomed boat may be helped to windward by assuming a vesica
      form when heeled:

      http://www.messingaboutinboats.com/archives/mbissueseptember15-
      98.html

      It may be that chine-runners, and even chine logs in a small way,
      reduce turbulence and help sail to windward. There is much ground
      for speculation in the absence of testing. However, PCB "knows more
      about sharpies than anyone alive", and if he knows he hasn't said
      (AFAIK).

      Graeme

      --- In bolger@yahoogroups.com, "saillips" <saillips@...> wrote:
      >
      > As we seem to have many multi-forum members, I'd like to ask the
      > Bolgeristas who have built Birdwatchers or other Bolger sailing
      > designs with external chine logs if they have found these to
      function
      > as "chine runners" (Paradox, micro-cruising forum)? I mean, do you
      > think they help sail to windward in thin water with the board up?
      > Just interested, and hopeful!
      > Thanks, David
      >
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