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. This forms the leeward side of the sail at all times, while the luff and leach edges alternate depending on the "tack" (shunt?). This has the one major disadvantage that the battens and mast still disturb the airflow on the windward (interior or concave) side of the sail. A second layer of cloth can be stretched across the interior edges of the battens to cover the mast and battens allowing the airflow to proceed across both faces of the sail with minimum disturbance and consequent drag.

 

The sail holds its airfoil shape in either direction because that shape is determined by the battens and the fact that it always presents the same "face" to the wind. The side closest to the mast is always the windward, high pressure side and the other is always the low pressure side, to leeward.

 

Todd's brilliant models and videos highlight the very small angular shifts needed to control the sail through all points of sail, including the shunt. The task for us collectively now is to build some full size boats to test the designs and work out the engineering of scaling it up. Of course we also need to work out ways of safely spilling excess power, dropping it quickly, reefing and possibly heaving to. Boy this is going to be fun!

Enjoy
Jim Baltaxe
They said, get a life. I looked on TradeMe but I couldn't find one.  

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From: harryproa@... [mailto:harryproa@...] On Behalf Of Doug Haines Sent: Sunday, 3 August 2008 1:31 p.m. To: harryproa@... Subject: Re: [harryproa] Re: Dyna rig sailing so is it two seperate cloths, 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:     http://www.runningt ideyachts. com/dynarig/   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: http://www.youtube. com/watch? v=lL8Av9Iv7SI http://www.youtube. com/watch? v=FcoBL_ILXbI http://www.youtube. com/watch? v=24rj28zBdbs http://www.youtube. com/watch? v=y2R6k9b99Tw        - Mike Doug Haines wrote: What do you mean double sided sail? --- On Fri, 1/8/08, Jim Baltaxe <jim.baltaxe@ vuw.ac.nz> wrote: From: Jim Baltaxe <jim.baltaxe@ vuw.ac.nz> Subject: RE: [harryproa] Re: Dyna rig sailing To: harryproa@yahoogrou ps.com.au Date: Friday, 1 August, 2008, 1:21 PM  Hi Doug &al   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.   It would appear to be very well suited to a proa but there are some exmaples of DynaRigs on monohulls, most notably the Maltese Falcon (http://www.superyac htsreview. com/maltese- falcon-and- the-dyna- rig_id18994/ introduction_ id236607) and a 65M Dyna Rig Clipper (http://www.yachtfor ums.com/forums/ general-sailing- discussion/ 7643-65m- dyna-rig- clipper.html). As far as I can tell these two boats use them more or less as high-tech square rigged sails although their battens do mean that they can be set fore and aft.   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 .   What is a Dyna rig?  Not happy with your email address? Get the one you really want - millions of new email addresses available now at Yahoo!

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