Anonymous wrote:
Jeremy Walker wrote:
Instead of having a rotating mast, I will go with a junk mast( fixed/unstayed), with the sail rotating, and meaning that there needs to be a collar and a rotating pin rail on the mast.
While working on some basic drawings, I would like to go back and have another glance at David's (Tyler0 JRA piece on development of his wing and hinged battens....... somehow I just cannot find it again.Can anyone help point out where it is on the site?
If you go to the members area and type in David Tyler Wingsails and their battens, you will come up with David's thread, called Wingsails and their battens, about working on his project in Canada. It is in the Wingsails Forum. You could also use the same search tool for other threads on hinged battens that should be in the Technical Forum.
The issue with using fixed masts on a standard junk-rigged shunting proa (not sure about your rig variations) is that the sail is on one side of the mast when going to windward on one shunt, and on the other when you change bows. Where to attach the halyard at the truck is the biggest issue I have not yet resolved. On a tacking boat, it works best on the aft side of the mast, offset to the same side the sail is rigged, on a masthead crane that is 30 degrees off centre. The halyard, yard hauling parrel and luff hauling parrel come down on the opposite side, sometimes called the chimney, where the sail never goes.
This obviously won't work for us. The closest I have come to a solution so far is to rig the sail on the opposite side of the mast to the ama. If you are standing at the bow of the main hull when the ama is to your right, looking back at the mast, and the luff of the sail is closest to you, the crane would be pointing towards you (port and starboard have no meaning here!), or possibly even slightly offset to your left. Need to make a model to determine where it will have the least twist on both shunts. The chimney that the halyard and running parrel tails use is behind the mast from this perspective. That is where the sail never goes. When you shunt, the sail rotates around the side of the mast that is closest to you.
There is some unavoidable twist in the halyard, but if you design it with lots of drift when fully hoisted, I think it might work.
I'll be very interested to see what you come up with.
Also, I have been reading a lot about the sailing of proa Madness, and it seems the boat sails perfectly well with just its mainsail. The jib acts like a turbo charger. So I can see no reason why you cannot use a single junk rig, with a balance of 10-20%, with the masty amidships. You could have a drifter for very light winds but I wouldn't bother. You won't get the blistering performance of Jzerro or Madness but I don't want it. A maximum of 8-10 knots would suit me fine. Madness and Jzerro have the daggerboard amidships in the ama. This will work obviously even with just one sail, but I am tempted by the idea of tandem daggerboards in the ama, with a space of perhaps 1.5m between them. Having sailed across the Pacific with tandem daggerboards, I know how easy it is to adjust balance with them. And you have a spare to bring you home if you break one!
Got you Graham, the fixed mast and rotating crane issue had been sorted(on paper) before mentioning the rig design here.
Normally I work things out on paper, and when I can construct something in a series of sketches, then I can begin sourcing materials and start building the thing in small scale).
Only then is it worth showing how it looks and functions, because snags will have been sorted, by then.
Sure, the masthead/crane and chimney need to rotate, along with the boom and battens, while the mast is fixed.
This is where the design is different to other junk and wingsails that I have seen, and is different to the Tystie rig, even if David's rig has a rotating masthead/crane and halyard on a bearing.
Help from David's work was in the way he explains how both the upper and lower first 10% chord distance of the wing's leading edge must hold a convex shape, in order to direct flow around to the upper surface.
His use of wishbones and 'riblets' to give the cloth shape, was helpful in that I can modify and hopefully lighten this system, to work with my wishbone boom, luffspar and yard, to make the whole wing rotate, including halyards and downhauls.
It may sound like a very big ask, but looks like a goer. (on paper)
Main concern as I see it, is whether the rig can be built light and strong enough, without going the all carbon composite route, and to find this out, a dinghy size build is the only way to show.
Doing an archive search, like you suggest, brings up some stuff going backbite a few years, when there were people taking up the harryproa idea of rotating unstayed rigs, but the use of boards manipulated to provide lateral. area balancing of effort centre and vector is the way that appeals me as well.
Having shifting sails is the old way that was used on the split rig Pahi, which does free up hull space for accommodation, if external drop or swing down boards can be used as well.
WWhat. appeals to me about a modified Pahi configuration is that both mast and boards can be external to the accomodation space.