Hi Dave,
I think you're under a mis-apprehension. There are two completely separate things in the folder.
One of them is one of my completely soft wing sails, as used on my monohull for 50,000 miles. It has a Wortmann fx77w153 section, a round mast, wishbones and battens made from alloy tube, with the amount of articulation controlled by Dyneema lines between the batten ends and the wishbones. The whole cross section of the sail is shown, no truncation. The sail is cut absolutely flat. If you want to learn more, please go to http://www.junkrigassociation.org and join the JRA as a "wingsail forum member", free during June, where I set up a forum to describe my rig fully, principally for Gardner's benefit.
The other is my idea (but only my unbuilt, untested idea) of what is suitable for a fast proa, because I think the above is not entirely suitable. The very small rotation of the mast is true only for this particular high lift/low drag, well-behaved E1210 section. I haven't been able to draw as good a setup using any other foil. I discarded it for use on a monohull, because it would have to rotate through inconveniently large angles; but what is bad for a monohull is good for a proa. Such a wingmast can certainly be stayed to windward, more easily than a wingmast that rotates through a larger angle. But because staying to leeward is impossible, the mast still has to be essentially an unstayed mast, for when you are caught aback. The stays are "helpers", to reduce the deflection of the mast under high sailing loads. The sail could be done in one of two ways:
1) a normal bermudan fully battened sail, as is well understood by sailmakers who make sails for wingmasts.
2. a sail that is based on junk rig principles, with stiff, straight heavy battens, each one sheeted, and with camber built into each panel of the sail using one of several techniques that we junk rig sailors now use. This decreases the demands on the mast, which can therefore be lighter.
--- In harryproa@yahoogroups.com.au, "David" <dave.pont@...> wrote:
>
> Hi David,
> a few layman comments / queries re your wingmast sketches.
>
> I am really surprised the wingmast only has to rotate 30 degrees. So the wing mast is only rotated 15 degrees from being completely horizontal to the direction of travel!? The wing mast - soft wing sail combination seems to work out well for a proa. One benefit: the mast does not need to be free-standing, it can be stayed?
>
> The jpeg shows detail of the wing mast. The boom is presumably truncated, compared to pdf image? The boom appears to project inside the mast and angle of rotation is limited by walls of mast? But this angle is less than that in the pdf image(s)?
>
> The pdf image shows a nice foil-like curve to the sail. Will sail-cut be used to create this curve?
>
> cheers Dave
>
>