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Re: [bolger] Re: External chines (runners?)

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  • Martyn Aldis
    In message , John and Kathy Trussell writes ... I have an Oyster Catcher built to Corned
    Message 1 of 8 , Sep 1, 2006
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      In message <00eb01c6cc92$25f87810$0a00a8c0@oemcomputer>, John and Kathy
      Trussell <jtrussell2@...> writes
      >PCB's essay on Light Dory in Small Boats states that the external
      >chines may reduce turbulance at the chines and add slightly to
      >stability, but I've never seen anything that suggests that they prevent
      >leeway.
      >
      >Conrad Natzio in England sells plans for various flat bottomed boats
      >and at one time had a flat bottomed pram with runners on the bottom
      >which he said allowed the boat to sail upwind. However, he has not
      >incorporated this feature in subsequent designs and I infer that the
      >runners were not that effective.

      I have an Oyster Catcher built to Corned Nato plans. There is far too
      little lateral area. Even an oyster could escape if it jumped up-wind a
      few times.

      The old off-centre board is becoming the rudder blade and a new tilt
      dagger board is under construction. It may even work.

      The other boat we have with external chines is a Tortoise and I think
      that may have too much "foils" area - I'm going to try a Mirror rudder
      as the large one on the plan is so sensitive.

      About deference to the designer's intentions. One great advantage of the
      books is that PCB gives us hints about why he did what he did and he
      often has variations on a theme. I would not put a full stern deck on a
      Tortoise again. It makes it very difficult to get the crew weight were
      it is needed running in a breeze and as we don't get ice in our harbour
      and do not go mud larding I have no need of the deck to flop on when the
      ice gives way or my boot hits a soft patch of mud. The Brick does not
      have the full deck.

      A modification I made on the Tortoise that worked well was to use the
      "New Instant Boats" smooth glass chine for the ends of the bottom and
      the original external chine for the sides. I've added topping lifts
      (Lazy Jacks) to the lateen rig and they are really worthwhile. I can now
      rig the boat with the sail in the lifts and wheel it to the water and be
      away fast and without the yard going in the sea. Similarly the sail
      doesn't smoother me at the end of the outing. This would have been
      useful in 1990 when we first rigged the boat and our son was a child.
      --

      Martyn Aldis, e-mail martyn.aldis@...
      ==============================================================================
    • graeme19121984
      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
      Message 2 of 8 , 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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