Paul,
actually, I can do minor adjustments to the camber on my sails, built with the barrel method.

On Johanna I reduced the tension along the battens with 10cm. This increased the bagginess. It also produced a number of wrinkles along the battens, and the vertical curve from batten to batten was closer to a semicircle than a trapeze. I think this improved her light-weather performance. On later boats, I have kept more stretch in the sail along the battens. There is now less wrinkles at the battens and the vertical curve looks closer to that seen on sails made by the shelf-foot (lens) method. The camber drops about 1/10, compared to when having the sail set up with no tension. On the three last sails I have made, I have used a cutting to give 9% camber and then stretched the sails along the battens, resulting in 8% camber when flying (the last sail, for Ingeborg, I have not tried yet.).

Actually I wrote about this subject in 2009.

Maybe it was good, after all, that I did not add broadseams along the battens, or I would not have been able to reshape the panels by pulling along the battens.

I guess my sails now are as close-winded as they can be without radical surgery. The mast is still there, robbing the camber at the luff on one tack ( that’s why I use quite little balance), and acting as a wind brake on the other one. My new aluminium mast for Ingeborg, at 150mm diameter (instead of 210mm of a wooden mast), at least reduces that drag.

Arne

The name of the game...

Paul, it just struck me that the pushrod you used on the first wishbone junksail could be the reason why the wishbone could not capsize.

I guess one should retain the new rope (‘tie-rod’), at least for this reason: When the sail is pushing on the lee batten, the tie-rod would let the weather batten add some support. This would let one keep down the dimensions and weight.

As for thinking that a 2-sail rig is better than a one-sail rig due to the slot-effect: I am a bit unconvinced here. My guess is that a sail with slot can produce higher total lift, but it may or may not produce a closer-winded rig than a one-sail rig. I guess it depends on how lucky you are with the camber of the single sail at the luff. Your method of using a ‘free-flying’ sail just aft of the luff (before touching the wishbone), with the curve set by the horizontal tension in the sail, sounds to be about as good as we can get on a thin-foil sail.

I hope someone will try this.

Cheers, Arne

PS: My fairly big sails surely produce plenty enough power, so need no slot for that. Still I wouldn’t mind reducing the tacking angle with a few degrees (Who would?). Today I tack Frøken Sørensen just at, or just inside 90° on the compass, in decent conditions. She is thus slightly closer-winded than Johanna, it seems.

The name of the game is...

HOW TO IMPROVE THE LIFT TO DRAG RATIO.

Arne: you might imagine that wishbone battens will capsize at some point because of their width but strangely enough they never have. So long as the sail is attached centrally at the ends the batten always stays flat. No I don't have or need any suspension lines for the upper battens and Mark, the topping lifts run on the outside of the battens. As you say it is difficult to estimate efficiencies but I would say the AeroJunk is the more efficient as it benefits from the 'slot-effect' provided by the narrow jib and from the two lift-generating centres - the luff area of the jib and the luff area of the main. Compared with Arne I have much smaller sail areas yet Miranda can reach maximum hull speed on a reach in a Force 3 wind. Cheers, Paul

Dear Paul,

My first windsurfer had an all aluminium wishbone which was very light.  The side where straight, the front end a large diameter which was formed from the same tube as the sides. The rear a separate piece, at a tight curve, as tight as the ali could be swaged.

Whilst efficient, light and strong, it did not look so pretty.  With the object of promoting the rig,  going with a nice curve is worthwhile.

Topping lifts.  Do these run inside or outside the wishbones?  If inside the upper ones would not have to taper so much.

Perhaps a difficult to answer question, but how much more efficient is the Aerojunk rig over the wishbone. 

Keep up the good work,

Mark

Arne, thank you for those kind comments. I believe the answer is even simpler than than you suggest. If you make the first 30% of the battens parallel sided, much like the letter u then fasten the luff of the sail to the centre of the 'nose', the sail will find its own perfect thin aerofoil profile. 

When allowed to curve a flat sail will 'shrink' in length by 2% for a camber of 1:8. If the batten is made to the length of the original flat dimension then the sail can be tightened from the leech to progressively flatten the sail if required. This will reduce the camber and move the position of maximum camber rearwards from say the 25 to the 30% point. This gives the owner plenty of scope for experiment and is effectively what the rear half of my AeroJunk battens look like. By making the battens this way the tie rod or line could be removed altogether.

Regards, Paul