Re: [bolger] Re: External chines (runners?)
- In message <00eb01c6cc92$25f87810$0a00a8c0@oemcomputer>, John and Kathy
Trussell <jtrussell2@...> writes
>PCB's essay on Light Dory in Small Boats states that the externalI have an Oyster Catcher built to Corned Nato plans. There is far too
>chines may reduce turbulance at the chines and add slightly to
>stability, but I've never seen anything that suggests that they prevent
>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.
little lateral area. Even an oyster could escape if it jumped up-wind a
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@...
- 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:
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
--- In firstname.lastname@example.org, "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
> 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