Subject: [harryproa] Re: Omer wing sail |
From: Mike Crawford |
Date: 1/11/2010, 9:37 AM |
To: harryproa@yahoogroups.com.au |
Reply-to: harryproa@yahoogroups.com.au |
Robert, --- In harryproa@yahoogrou
Thank you for posting the omer link.
I had written this design off over a year ago because larger designs
use either electrics or hydraulics to induce camber. I would not want
a rig that depends upon either system on every tack or shunt -- too
many things to go wrong.
On smaller boats the site says the camber can be induced by a hinge
at mid-boom, though, so perhaps there are other options.
As long as we're theorizing, do you think the auto-camber could be
done on something the size of a larger Harry with a bruce number
approaching 2.0? Some thoughts:
- Strong hinge.
I suppose the loads are known, so perhaps there's
nothing preventing the design of a really beefy mid-boom hinge that
would auto-camber in most winds. Perhaps with a continuous-loop
control line to force camber when the wind is really light.
- Hinge with vang.
There could be a strong hinge as with the
previous idea, but with some sort of vang system to carry the bulk of
the vertical load, eliminating a lot of torsion from the boom. The
vang would take up extra space below the boom, and would somehow have
to expand and contract to allow the mid-boom hinge to swing from one
side to the other (a fixed vang would make this impossible), though,
and that is definitely a design wrinkle.
- Wide boom with traveler.
It would look a little funky, but you
could have a twin-boom extending aft like a thin pie slice, with a
curved traveler at the aft end that attaches to the mainsheets. The
boom itself would definitely have a major vertical flange/wall on its
outer edges, essentially being two booms in one. Whichever flange/wall
is windward would then handle the vertical loads on each respective
tack. The
would then automatically migrate to windward with the force of the
mainsheet (with the boom taking vertical loads). This obviously makes
for a larger and heavier boom, but: a) at least the weight is not high
aloft, and b) the width of the boom might add a nice end plate
effect. You could also have a line on the traveler to force it to
windward
---
Today I'm pretty excited about the wide boom with traveler. It's
about as simple as you can get in terms of shunting, number of moving
parts, and system design. It wouldn't have the low loads of the junk
setup, but it also wouldn't have the extra parts and drag from the
sheets. [I'm not arguing for or against the junk -- I'm just excited
about a modified Omer at the moment].
It would be great to have noticeably more lift and less drag than a
standard sail, all while sailing at a 10-degree angle of attack instead
of a 20-degree angle.
This could be the super-fast-yet-
- Mike
robertbiegler wrote:
> But I actually wasn't thinking about a whole new system.
I found a link to a soft wing sail that its designer calls "ready for
production": http://www.omerwing
The flexible batten for the aft portion of the sail doesn't work
with junk-style sheeting, for the reasons others have already
explained. It does work if you set up your soft wing like a standing
lug, as Chapman did in the 1960s. There is information on this rig in
old AYRS publications.
Another alternative is to use rigid bent battens and let them flip
along their longitudinal axis. Nils Myklebust has published drawings in
the latest JRA Newsltter, and plans to make his next sail that way.
Jeff Doyle developed another soft wing, based on what a Chinese man
told him about his grandfather'
Regards
Robert Biegler