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how can it hold a aero foil shape in both directions?
--- On Fri, 1/8/08, Mike Crawford <jmichael@...> wrote:
From: Mike Crawford <jmichael@...> Subject: [harryproa] Re: Dyna rig sailing To: harryproa@... Date: Friday, 1 August, 2008, 9:18 PM
The double-sided sail basically looks like a large symmetric wing sail.
If it were on its side as an actual wing, the longer convex side would be on the top, while the shorter concave side would be on the bottom. In this case, the sail is angled almost into the wind, with the longer convex side slightly to leeward, and the shorter concave side slightly to windward.
Unlike wing sails and airplane wings, the shape is symmetric. So as Jim points out (in a great explanation -- thanks Jim), either edge of the sail can become the leading edge.
If you look at the bottom picture at http://tinyurl. com/5khcw4 , you can get a good view of the leeward side of the sail while beating.
Some dynarig designs only use a single outer/leeward skin, such as the example
at:
Regardless of whether the sail uses one skin or two, the key is the cambered shape with the unstayed mast in the middle. This provides a fine leading edge in both directions that allows the sail's camber to create lift, and does so without the turbulence of a mast in front of that edge. The arms/battens which connect the sail to the mast enforce the camber to keep an efficient shape.
Dynarigs, as well as double-sided wing sails will produce more forward drive and less heeling moment than a conventional rig.
Some people claim that a properly-cambered double-sided sail will produce twice the forward lift of a conventional sail on a normal non-rotating mast. Others claim that the drive is only 20% to 50% better,
but since the sail creates much less heeling moment for a given amount of drive, you can use a much larger sail, and therefore get a lot more drive.
I'm not an expert, and I make no claims. But I will say that Todd's comparison of the dynarig to an easyrig was most impressive:
I'll take a shot at defining it. I'm sure the others will correct me if I get anything wrong (and probably will do so anyway just on general principles, seeing as it is the harryproa list).
The DynaRig is a double sided, fully battened sail similar to the Bolger (proa) sail in that either edge can be the luff and the same face of the sail is always windward. The battens extend horizontally from one luff edge to the other and are built with a fixed curvature and, most distinctively, are attached to the mast so the entire rig moves as a single unit. This results in a sail with a known and fixed shape regardless of angle of attack to the wind. This rig is reputed to be extremely efficient although I don't know of any objective comparisons with other similar rigs, Bermudan, Una or Easy/Aero.
The downsides appear to be expense, complication and weight aloft as well as questions about tacking or shunting with the full face of the sail exposed to the wind, as our discussion has already pointed out. It does seem, however, that the fixed (to the mast) battens address some of the stability problems that plague the Bolger proa rig.
Todd's videos show the sail shape and operation brilliantly.
All in all this is another very strong reason I have to get my A into G and get Harriette built this summer.
Enjoy Jim Baltaxe
They said, get a life. I looked on TradeMe but I couldn't find one.
From: harryproa@yahoogrou ps.com.au [mailto:harryproa@ yahoogroups. com.au] On Behalf Of Doug Haines Sent: Friday, 1 August 2008 2:21 p.m. To: harryproa@yahoogrou ps.com.au Subject: Re: [harryproa] Re: Dyna rig sailing
The double-sided sail basically looks like a large symmetric wing sail. If it were on its side as an actual wing, the longer convex side would be on the top,...
so is it two seperate cloths, how can it hold a aero foil shape in both directions? ... From: Mike Crawford <jmichael@...> Subject: [harryproa] Re: Dyna...
Hi Doug &al A Dyna rig can have either 2 or 1 separate surfaces. The simplest version has a single cloth on the outside of the shape formed by the battens....
Hi, Has anyone sorted out how to reef a dynarig? I know that the method used by the maltese falcon where each section of the sail is controlled by a motor that...
One option of a dozen or so possiblities I may explore is having the battens (more like wing spars) built to have mast go through wing spars riding on rollers,...
That would still reef the bottom sails first, wouldn't it? The idea of reefing the top first seems nice, but I guess I am not sure what advantage it has other...
You bring up good points about apperent wind, gybing, and sailing seeing full force of wind at low speeds. But it was the sail action in both traditiinal boat...
Perhaps I missed this earlier: How is a dyna rig controlled? Does it feather into the wind at all? If so, is this not scarry? Would a junk / dyna rig be the...
Hi, Â Looking into what the pictures show for rarebird - now understand what breaks. Looks pretty good to me, except rudder and half-case sort of dangling...
How important is it that the dynrig have the yardarms rigidly attached to the mast? The reason I am asking is it seems that if you take a dynarig and put it on...
Hi I'll just put my replies at the top. I'm used to usenet, where interspersed replies are normal. I appreciate your "not to be rude or demeaning" sentiment,...
Todd and all, May I suggest that a long skinny symmetrical hull is and acts as a low aspect foil. That is my empirical data again provided just two days ago. ...
John, You are absolutely correct. If the boat does not move forward and is pushed exactly perpendiculary to the hulls by the wind, the symetrical shape of the...
The Maltese Falcon has plenty of space between the sails so that they could rotate each mast/sail independent of each other in a tack. I was thinking that...
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