I worry about what will happen with a dynarig during a shunt when the wind picks up.

  With an una rig or easy rig, you can go completely neutral by loosening the mainsheet and allowing the rig to weathercock.  At any time, at any point of sail.  This is one of the reasons why I'm a fan of a proa with an unstayed rig; no matter what you're doing, you can quickly stop dead with a neutral rig, and/or back up.

  With the dynarig, the full area of the sail goes perpendicular to the wind during a shunt.  That might not be a big issue in moderate winds, but if you get a gust at that moment, especially if the ww hull is on a wave, the results could be most unsavory.  Even if you don't get knocked down, that's a lot of stress on the rig when the boat isn't in a position to defuse that stress by sliding leeward.

  An illustration of this is at:

    http://au.groups.yahoo.com/group/harryproa/files/%20Dyna%20rig%20testing/

  The group discussed this a bit last summer, but I don't recall anyone offering a logical argument as to why the dynarig would be safe in this situation.  There were opinions about it not being a problem, of course.  Todd was most in favor of the rig, and said that it was not a problem during his many tests (which were a great addition to this group; I'm sorry he's not yet participating again).

  The Maltese Falcon can deal with this in one of two ways.  Either:  a) turn only one mast at a time -- it's a huge ship, and can easily handle 1/3 of the sail area going perpendicular to the wind, or  b) press a button, furl the sails, turn the masts, and then press another button to unfurl.

  Given that a fast/light/inexpensive proa won't have the weight or the pushbutton sail handling of the Maltese Falcon, I'd have a hard time being the person to take a leap to the dynarig, at least on a boat with accommodations.  Perhaps a harriette would be a great proving ground for the concept.

  Then there are the issues of weight aloft, concentrated points of stress at the battens, added complexity, and less-convenient furling.

  I'd love the efficiency of a double-sided sail with perfect camber, but my spending will likely vote with a system that is much simpler.  It's hard to beat a mast with a bolt rope luff for sheer simplicity and ability to repair damage one's self.  Reliable track and slides/cars follow closely behind.

       - Mike

 

Gardner Pomper wrote:

Yes, I do keep coming back to the dynarig. It is appealing. I am, however, concered about how it will behave if caught aback. I hope to build a small one for my test proa this summer (if I ever get the rudders and crossbeams built).

I have thought that if the dynarig battens where flat horizontal plates, wide enough to go around the mast, then a slot could be cut in them allowing the whole sail to cant away from the wind, putting the center of pressure aft of the mast. It would seem that would make the sail auto feathering.

All the arguments about weight aloft, mast stiffness and weight and complexity still argue against the dynarig, though, so I am firmly in the undecided camp.

- Gardner

On Tue, Mar 24, 2009 at 8:10 AM, jrwells2007 <jrwells2007@yahoo.com.au> wrote:

This balanced rig is designed to work with the wind from either side of the sail as for the Easyrig. The Maltese Falcon appears to get much of its benefit from being single sided - that is the wind only works on one side of the sail. This allows the sail to be asymmetric with permanently curved spars.
I do like the thought of an asymmetric sail on an asymmetric hull (a proa).

--- In harryproa@yahoogroups.com.au, Geoff Lowe <geoff@...> wrote:
>
> This balanced rig looks a little like the modern iteration of the square rig
> used on the Maltese Falcon (http://www.symaltesefalcon.com/index2.asp),

> except that it is a main/headsail combination rather than a single Œsquare¹

> sail centred on an unstayed mast. In fact the Hoyt balanced rig previously
> discussed on this forum (http://www.garryhoyt.com/id19.html) is even more
> like a square rig, albeit a little asymmetric...
>
> Geoff Lowe
> Infotools Limited
> +64 9 488 1772
>