Hi Mike
I am with you on this rig: you could get away with rice bags and still have a reasonable shape; the sheet loads are lighter; it's easily reefable; if the top section rotted out, it would be easy to replace without wrecking the lines of the sails; there's no sail track to buy or jam; and the battens can be low tech. The strings need not be a big source of drag with dyneema but one would need some gloves. I will have to make up my mind before I start trying to set up for making the masts. A simple tapered section makes the most sense and it wouldn't need the bearings of a lot of other rigs.
Apart from not being common I am not sure what the problems with it are for a cruising rig. Some people swear by junk rigs and this makes more sense to me than a straight junk.
Robert
--- In harryproa@yahoogroups.com.au, Mike Crawford <jmichael@...> wrote:
>
>
> Another benefit of the swing wing rig would be new options for sail
> cloth.
>
> Given that there are no extreme loads on the sail, and that the
> wishbones will maintain sail shape, a good foil shape won't have to rely
> on extreme materials, perfectly-cut sails, and computer-designed
> reinforcing fibers along load paths. No mylar, kevlar, carbon,
> technora, or other exotics necessary.
>
> In fact, looking at that reefing system, my guess is that soft
> sailcloth without impregnated polymers would work best. This would
> allow many more reefs, folds, and other uses without damaging the sails.
>
> Since the wishbones hold the shape, you could use heavy-duty sail
> cloth without worrying about wind shape in really light winds. Along
> the same lines, you could use super-heavy-duty sail cloth for the top
> storm reef, thereby truly having a single sail that will truly work in
> all winds.
>
> Thus, heavy-duty soft Dacron or Dyneema should both work.
>
> Dacron does not have the highest modulus, so it stretches in big
> winds, but that will be less of an issue with lighter sail loads and
> wishbones for shape.
>
> Dyneema has a great modulus, and is just about impervious to UV light,
> but it can creep over time and lose some shape if repeatedly subjected
> to high loads. But if the sail is lightly-loaded, and the shape is
> provided by frames, the creep should be a non-issue.
>
> So you should be able to use reasonable sail materials and still get a
> high performance sail that lasts a really long time, even with extended
> UV exposure. That's always a good thing, and particularly nice if
> you're going to be sailing reefed a lot -- you wouldn't want the top 2/3
> of the sail to age quickly and then replace the whole thing.
>
> There would also be little or no flogging, which is hard on all sail
> cloth.
>
> Ack! Every time I mentally write this rig off, a new reason to use it
> crops up. Perhaps the savings due to sail cloth, a simpler mast, and no
> sail track or bearings would cover the cost of designing the rig
> properly./ /
>
> Rudolph and Kim: I curse you (in a good way, of course) for arguing
> for a new option that unsettles my previous "fixed" plans.
>
> - Mike
> / /
> / /
> On 5/26/2010 10:42 AM, Mike Crawford wrote:
> >
> >
> > Gardner,
> >
> > The other antidote to your sail area and mast height conundrum could
> > be the swing wing rig proposed by Kim and Rudolph.
> >
> >
> > http://wharrambuilders.ning.com/profiles/blogs/sailing-with-pha-tiki-30-n119-1
> >
> > In theory, this will create noticeably more lift than a single-skin
> > sail, and do so with noticeably less drag. Bertrand Fercot's
> > experience bears this out -- he noted that he could sail his Tiki 30
> > faster and tack easier than another Tiki 30 with a traditional Tiki rig.
> >
> > You'd also have more lightly-loaded sheets, a simple reefing system,
> > lower loads on the sail, no need for a boom, and a round mast (no
> > "sailing" while moored) without rotating bearings. The sails would
> > also keep their near-perfect shape even in extremely light winds. And
> > given the greater efficiency of the sail, you'd either be faster at a
> > given mast height, or the same speed with a shorter mast. That's
> > something to consider.
> >
> > It might not be extreme on a dead run, but given that a powerful
> > multi can sail faster by tacking downwind than by running, and that
> > these sails will hold a nice airfoil shape at a better angle of
> > attack, this would probably make a proa a great downwind boat in most
> > directions.
> >
> > I can't decide if I'd be willing to make the leap. All the theory
> > appears to be correct, but it would mean either lots of
> > trial-and-error on your own, or alternately, working with a sailmaker
> > who could analyze the sail's performance in an airflow, specify the
> > right wishbone shape, and then cut the sails to match.
> >
> > But Rudolph, Kim, and Fercot make good arguments.
> >
> > - Mike
> >
>