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

[brian eiland]

> Brian had written:
> I didn't chose to make this comparision at first. If you look back a few
> threads you will find I was responding to an inquiry from an interested 
> party that demoted the DynaRig and my mast-aft concept in favor of the
BiPlane  rig.
> That's how the subject came up.

Allan responded:
 > I think that I may be the guilty party Brian is talking about. I am not "an
> interested party" nor did I "enquire"  , in fact I responded to an off-line
> (I think, - mail that Brian sent.)
________________________________________________

Brian replied:
Lets revisit the posting I made:

SUBJECT: DynaRig, 40-ish Catamaran motorsailer 

Hi Brian, 

I am of the definite opinion that all these rigs you talk about are 
inefficient and heavy, not what one wants on a catamaran. It has been 
proved time and again, what makes an efficient rig for windward work, a 
wingmast and a sail of high aspect ratio, and some means of minimizing tip 
vortices. 

Why make it more difficult? 

I have decided to go for a bi-plane rig on my 45 ft. cat, using unstayed 
masts, and the masts will have a wingshape. The masts and booms can turn 
360 degrees. Can easily be released and reefed at any angle to the wind. 

XXXX  (Allan) 

_______________________________________________________________ 
Brian replied: 

Actually XXXX (Allan) I am not trying to "make it more difficult". I am just
following aerodynamic principles that end up leading me to the rigs I chosen
to promote and expand upon. I try to consider these rigs in light of cruising
sailboat designs rather than racing designs, or specialty applications. 

I'm having trouble understanding your choice of a 'bi-plane rig'? I
understand
the desire to get a lower COE of the total sail area, and I do know these
rigs
have distinguished themselves in a few specialty applications (smaller
vessels, and a few speed record seekers), but at what cost to all-around
performance on a cruising vessel?? (I believe this is the type of vessel you
are seeking?) 

The bi-plane rig can certainly be made to perform to windward. And the use of
higher aspect ratios and wingmasts will assist in this effort. But now you
have tall narrow triangular sails that are the worst form, that produce
considerable induced drag from vortices off of their tips, and you have two
of
them. Your induced drag on this bi-plane rig is going to be considerable
higher than a single free-standing uni-rig. 

My real concern with the bi-plane rig is with its performance in reaching and
running, two of the primary and preferable sailing angles for cruising
vessels. I just do not see any way to make the leeward twin rig effective at
all in a beam-reaching situation. And remember EFFECTIVE downwind sailing is
not just about projected sail area to the push of the wind, but rather FLOW
over the sails, that will not easily be attainable with the bi-plane rig