[MHml] DynaRig, Mast-Aft, Bi-Plane sailing rigs

[brian eiland]

Brian had written:
> The email I sent out on the Dynarig was meant to show how the Falcon's
> Dynarig could be brought down in complexity, price, and weight. Certainly
it
> is still a 'square rigger', a very modern version at that, and will never
> compete with a free-standing unirig in expense nor weight aloft. But it has
shown its capabilities in performance, and on all 3 points of sail.

Rob replied: 
> You could have added that not only is it vastly more expensive and many
> times heavier than the unstayed biplane, it is also much less safe,
> unreliable, hard to handle, with very high maintenance and will not perform
> as well on any point of sail, including reaching. 

Brian replied:
The Dynarig appears to be doing very well in the St Barts trade winds
<http://boatdesign.net/forums/showpost.php?p=142295&postcount=94>
(I belive that 3rd photo might be a power reach). I could probably find a few
more such photos as well.

On the other hand here are a few observations on the bi-plane rig:
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<http://www.boatdesign.net/forums/showpost.php?p=89886&postcount=20>
Biplane rig 
Thomas Firth jones tried such a rig on his coastal cruising catamaran named
Dandy, but after two seasons gave up on it. Apparently it works best on very
fast cats because, along with the faster speed comes an aparent wind that is
further forward. This may explane why it is given so much praise in the faster
sailing multi community.

The boat in question will not be nearly that fast. Most likely it will be a
D/L 100 boat or damn near. Especially when all the long voyaging stores are
loaded aboard. Although it will most certainly be faster than a mono pocket
cruiser of the same length, it will probably be too slow to benifit from the
biplane rig.

Mr. Jones reports in his book MULTIHULL VOYAGING: "...On a reach, the leeward
sail flopped idly about, and we were driving the boat with only half her sail
area..." 

And there was much more after that. And most of it wasn't flattering. The only
good thing he said about the rig was how few times he had to reef it.

Its best point of sailing was dead down wind, because the two side by side
mains could be flown wing and wing.
Bob
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<http://www.boatdesign.net/forums/showpost.php?p=93221&postcount=22>
Biplane rig 
This rig seems appealing in theory, but as Tom Jones discovered, it has
certain drawbacks in practice. I don't think faster boats can entirely sail
away from the lee blanketing problems on a reach. I've read correspondence
from a person in Thailand who built a Radical Bay (Schionning design) and
still acknowledged that the problem occurred. They were overall very happy
with the design, however, and felt that this inefficiency was a tradeoff that
could be endured to get the other advantages of the rig.

One big disadvantage for a cruiser is that when the lee sail is outboard,
there is very little deck underneath it to work at the boom, for reefing and
sail shape controls. A great advantage of cats in general is that you can
stand by the boom in the middle of a wide deck and do this work in security
and comfort, and that is a big advantage to give up. 
Ray
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...and finally

> Peter Nice: I designed and built W, the prototype bimaran.  It is a cat
with
> the rig in one hull,  not an ama less tri.  For what it is, it is an
> interesting concept, which taken to it's logical conclusion, becomes a
harry
> proa.  

'Nuff said. Rob
 
Brian replied:
Lets not confuse the 'biplane rig, with the 'bimaran'...two different subjects