Doug,
ANCIENT VERSUS MODERN
If a junk rig is cut properly, in that the sail is allowed to
curve smoothly in an airfoil shape, what's the difference between
the junk and a fully-battened high-tech sail?
Not much. Both rigs use battens to keep shape, going for an
airfoil that will product lift. A lot of the square-top sails even
have one or two upward-pointing battens as well, almost junk-style.
The high-tech rig will use sail track with batten cars, and have a
highly-stressed sail with one sheet; the junk rig will use some
system of parrels/hoops, and several sheets, with a sail that
carries less stress. The junk's heavier battens mean more weight
aloft, but also make it easier to handle and tack. The
battened-main's lighter and more flexible battens mean less weight
aloft, and perhaps a slightly more efficient shape, but at the
expense of being more difficult to handle and tack (in light wind,
some fully-battened mains need a LOT of help to get the battens to
flip over).
And it is indeed possible to get a good sail shape with a junk.
Check out the smooth curve in Badger's schooner-rigged junk sails:
https://picasaweb.google.com/108735432675049110317/Badger#5518116655093321266
If cut a bit differently and tugged properly, that could be a
great sail shape. Others have done even better in getting a smooth
foil, but unfortunately I don't have any photos.
It's not about ancient-versus-new. All sails are ancient. A
modern junk rig is no more or less ancient or traditional than a
modern marconi-rigged sloop. In either case, you could choose an
older non-optimal design, with a traditional shape and profile, or
you could choose a modern optimized design, with whatever profile
suits you. Marconi rigs don't have to look like really tall skinny
triangles, and junk rigs don't have to look Chinese.
Why does Brett's boat go so well? I don't know. My guess is that
is means a lot to have good sail shape, no matter what the wind, and
he can do that because his sail is adjusted and cut well.
UNSMOOTHNESS
I'm not sure if you're talking about a traditional junk or the
swing-wing.
For the traditional junk, the sails don't have to be un-smooth.
You need to cut the sail properly, with batten pockets that allow
the sail to take an airfoil shape (or flexible/segmented battens),
and definitely make sure everything is tensioned well.
For the swing-wing, there will likely be a bit of a wrinkle on the
windward side.
But isn't there the same "wrinkle" where the aft edge of a wing
mast meets the luff of a battened mainsail? One has a slight
wrinkle, the other has a gap with a luff rope and batten cars.
Neither is perfect. The ideal wing would be smooth on both sides,
but currently there is no low-cost ideal wing sail that's easily
raised, reefed, and stowed, by one person, in heavy weather.
The question is whether the soft wing is more efficient than a
standard fully-battened main. Look at this leeward edge (image
repeated from previous post):
http://api.ning.com/files/OX6wi*XepeSFiOcN2A1LCruxG28UbW2T02hM1KC3mXMkg5J5D*9b2qh2350oH2Rv9oBLKC3AuWV9WVK3HiLPURXItsWuRpJb/178f2009042200PHAwithitsnewdoublewisbonesintandem.JPG
How often do you have a sail shape like that on a normal
fully-battened mainsail in light wind? Even if I work really hard
with my mast rotator, halyard, cunningham, and outhaul, I still
can't quite get that shape in light wind. And if I do get that
shape, I'll have to hang off my boom like a monkey to get the
battens to flip over on the next tack.
Plus, Omer's polars are most impressive. Even if the swing wing
doesn't completely match the Omer, it's going to be an efficient
sail.
---
That's not to say that you should like either a standard junk or
the swing-wing. But I wouldn't pan them because of a wrinkle or
two.
A properly-designed junk rig, with a good sail shape and some sail
area in front of the mast, has benefits to a cruising proa, or
racer-cruiser, that other rigs don't offer. That doesn't mean it's
the only rig -- just that it can be surprisingly efficient, easy to
handle (whether for lazy sailing or emergencies), and low-cost.
If you can up the efficiency of the junk even further with a full
double-skinned airfoil shape, it might even be superior to other
rigs, even on just a performance basis.
- Mike
Doug Haines wrote:
|
Yeah, Maike, so what I was asking was how does
Brett's boat seem to go so well?
Or why would people choose that strange
unsmoothness?
--- On Fri, 27/5/11, Mike Crawford
<mcrawf@nuomo.com> wrote:
From: Mike Crawford <mcrawf@nuomo.com>
Subject: [harryproa] Re: Swing-wing rig....junk
To: harryproa@yahoogroups.com.au
Date: Friday, 27 May, 2011, 10:48
Doug,
From what I can see on Brett's NZ proa,
he's got a standard single-skin junk rig
that doesn't create an airfoil shape. If
that's true, the sail would indeed be
pushing against the mast on one shunt and
pulling away on another.
The swing-wing is a different design,
though, with double-sided wishbones that
create a sail with two skins.
The way the wishbones work is that the
leeward edge of the sail has a nice smooth
curve to it, while the windward side gets
the kink. This is less than ideal, but also
still a better airfoil than a single skin
sail. For each shunt, the leeward surface
is smooth.
To get a better idea of how it works,
check out these photos:
Nice leeward surface for generating
lift:
http://api.ning.com/files/OX6wi*XepeSFiOcN2A1LCruxG28UbW2T02hM1KC3mXMkg5J5D*9b2qh2350oH2Rv9oBLKC3AuWV9WVK3HiLPURXItsWuRpJb/178f2009042200PHAwithitsnewdoublewisbonesintandem.JPG
Corresponding kinked windward surface:
http://api.ning.com/files/8ZicrvcPCMAFxbwHBScmeROW*xJLvh1BnaXKVECpl9rETD3muuQn3pqV0nlR3LNyk6JoZyiD-TBUivh0Bmsl8yxjrNX*bsNh/178gUKJRA0002.JPG
Interior (to see how things might push
against the mast):
http://api.ning.com/files/-1yR27opppagPAzdnm*JUW1PwlPrg*WP4CHraDW*Yptmb-pI6CheiXxsLX2itDcZSVU3AbJyOktv7NdXUO*0KzkHniwieOY0/176b200806010037.JPG
- Mike
Doug Haines wrote:
|
For the unbelievers, I
might say that the thing
looks like a pile of crap -
but somehow seems to go
alright (James Brett's NZ
proa on youtube) and get's
favourable comments.
How can the sail have
good curving when it has to
go on one side of the mast -
which looks ok one one
tack/shunt, but then it
pushes into the mast and
must make a huge kink in
sail shape when on your
other tack(shunt)?
The battens would be
pushed up hard against the
mast (like sail against
spreaders on normal boat).
The tack with the wind
cxominjg from ......need
drawing.
Wondering if we could
infiltrate Sailing Anarchy,
just so as to use more photo
uploading things
DOug
|
|
