Rudolph,
You make a strong argument for the swing wing. No rotating mast
bearings, no boom, no worries about mainsail tension, and lower loads
would all be great things. As would the efficiency of a wing sail,
which is the primary reason to look at the swing wing in the first
place.
I was fascinated by junk rigs a while back after reading Annie Hill's
book, but then stopped paying attention when I read of several people
getting junk rigs and then abandoning them because of their upwind
performance. I understand that the Hill's cruising habits made the
upwind performance less of an issue, but I've got a lot of upwind
sailing to do on each trip where my boat will be moored, so I can't
ignore that limitation.
The swing wing design, though, should take care of any upwind
worries, and should be faster than a standard rig on a reach.
Alternately, it should have less drag for the same amount of lift, and
therefore lower loads for the same boat speed.
If the sheeting can be simplified in terms of what needs to be
cleated, while still keeping the benefit of multiple sheets on the
sail, each with smaller loads, this could be quite an impressive sail.
Now that I look at the PHA photos again, I can see that only two
lines on each side are sheets, and neither has a winch on it. It's
possible that the two lines are actually the same line, and can be
pulled together when taking in a lot of slack, an individually when
there's more force on the line. I can't tell.
I'd been thinking of complexity and failure points in terms of
numbers of strings, frames, and battens. But now that you mention the
strengths of the swing wing, I can see that's only part of the story.
Getting rid of rotating mast bearings and eliminating boom stresses
also adds to simplicity, as does the elimination of the jib.
Spreading the same load over multiple sheets could actually reduce
opportunities for failure, as would the lower stresses on the mast due
to the efficient foil shape. Getting rid of the need for all that
mainsail tension would also be a great thing in terms of reliability.
My hat is off to Bertrand Fercot for implementing the rig and testing
it for years.
Thanks Rudolph and Kim for explaining more details, and Gardner for
continually revisiting questions and forcing a discussion.
However, I'm still hoping not to be first in line with this one.
- Mike
Rudolf wrote:
Hi Mike,
I would say the Wharram would be cheapest, and worst performer.
The big wing mast would be much more expensive then the others. It is
the highest stressed rig in the comparison.
The swing wing is a junk rig with the low loads and lots of sheets.
Junk rigs are great as they have a way of dividing the loads so that
there are no high stressed parts.
So it is not the absence of a boom that makes them cheaper, but the
uncomplicated way of building the parts.
I am sorry to say I never saw such a rig in real life but I expect it to
be very docile when sailing and feathered.
There are junk sail sheeting diagrams around showing multiple sheetlets
being diverted through blocks ending up in one single sheet. That could
solve the complexity when shunting.
Safest on a mooring in a big blow is to lower your mast, and that could
probably be done with this rig as you don't need a rotating mast.
But I think it is more important that when sailing the swing wing will
be much easier to reef because high stress rigs with full battens will
always bind on the mast. Although I must say that BD's ail comes down
quite well.
Efficiency is not defined by the number of sheets on the sail, but the
ease of use combined with performance.
The shape you can have with this type of rig is great, and will be
better in time.
Because the sheets are lightly loaded they are easy to adjust, probably
can be arranged so they don't need much attention.
Hoisting this sail would be a matter of pulling a rope tying it off and
that's it. On many (small) boats you are working a winch just to get the
main up. Tensioning it is loud enough for everyone within a hundred
metres to hear.
That also has to do with efficiency, and wear.
In the end the low stress stuff will outlive everything else. And
probably without much loss of performance.
Again this is based on second hand information, but the Chinese sailed
with these rigs when we were floating around on tree trunks...
regards,
Rudolf