My last posting here may not have been so enthusiastic with respect to the SJR.
The reason is that I don’t see much room for a dramatic, game-changing improvement over the present cambered sails. The dramatic improvement was achieved in 1988 when Paul McKay fitted his flat (Hasler style?) sail between a number of wishbone battens. These wishbones limited the sail’s shape to the camber Paul wanted (See NL 17, p.28). There was a big photo article about his Fever in Practical Boat Owner. In NL 17, Paul also briefly mentions the possible introduction of hinged battens. It was this, which gave me the idea to modify my flat sail for Malena to take hinged battens (NL 24). I reckon that the upwind performance gain with camber to be around 20 to 50% over that of the flat sail. This gain was retained when I introduced the cambered panels between straight battens.

The SJR has not shown such a dramatic improvement in upwind performance over other cambered junkrigs, as far as I have seen. Since a Johanna-style sail can have 5-10% more area for a given mast, my hunch is that this extra area may well make up for any added performance of the SJR. Big is beautiful.

If only we could have a racing class with identical hulls, free mast length (round), and a fixed sail area. Then one could see which sail was best. I guess I would put my money on David’s Weaverbird rig.

Fun facts:
The JR schooner Samson, in Stavanger is the only schooner I have sailed on. I never made any accurate measurements, but every time I sailed one her, I was surprised over how close-winded she was. Later I came to think that with only two sails, Samson was in fact a 2-masted sloop. Chew on that one...

Arne

..a two-masted sloop...

Karl wrote:

In regard to schooners not performing well to windward compared to a single masted rig, you are talking about different beasts there. For the same sail area one is a low aspect typically high drag rig while the other is the opposite on those two counts.

Then you have the SJR compared to Contiguous Rig and you have two high aspect sails working together compared to a relatively low aspect sail, working alone. You can't have a higher aspect sail without a longer leading edge so to suggest better performance because of the leading edge length means you must be talking about a higher aspect sail/wing/s. The two are very essentially entwined. But I probably should have said, I suspected the SJR performed better because the sail area is divided between two high aspect sails which added together, give twice the leading edge. 
  

In a JR schooner or ketch, both sails have to be high AR to fit onto the boat, so I don’t think this holds good. In fact the reverse is true. Both masts have to be around the same height as a single mast to get the same area as a single JR sail, so that single sail tends to have a lower AR - whether it’s split or contiguous. And yet that single sail is better to windward.

No, I don’t think that the SJR is two high AR sails, it’s in fact one aerodynamic package that happens to have a slot in it, just as aircraft have wings with moving flaps (but for entirely different reasons, to maximise lift at times when drag doesn’t matter so much as it does in level flight, that is, on takeoff and landing).

But yes, the way to get full benefit of all that LE length you think you perceive in the SJR is to put one on top of the other - and then you get something like a glider’s wing which is extremely efficient but impractical as a planform for a sail. Anyway, this is why I advocate for the highest practical AR whatever the type of JR you fancy. It decreases helm imbalance off the wind, as well as increasing upwind efficiency. In your position, with a mast length intended for triangular sails, I think it’s worth taking full advantage of it and going for maximum AR.

...but where is the plausible explanation for the experimental result? The answer may be in the paper David refers to. That's a bit above my ability to really comprehend so I don't know. It did seem though, from the little bit of the experiment actually shown in the video, that those tell tales were flying quite nicely and maybe the jibs really were helping there. I have never really thought the so-called "slot effect" had much to do with the SJR, but maybe it does a bit.

As far as I remember, Slieve reckons that because the jiblets of the SJR are out in clear air, unaffected by the disturbed air around the mast, they work better, which is why he pushes for their size to be the maximum safe percentage of the whole rig (and why there’s nothing as good as a large genoa for hauling a boat to windward). The mainsail is only there to get the balance right and to complete the aerodynamic equation, upwind; it only really starts to drive once the sheet is eased as the boat comes off the wind. 

Karl set the test “boat" and fan at an angle of 45˚ to each other, as he says this is the angle of the true wind to the boat when going to windward - well yes, but in fact the boat is not stationary like his test piece, but is moving forward; and sails relative to the apparent wind, which is somewhere in the region of 30˚ - 35˚. An apparent wind of 45˚ is more of a close reach.

I think David is 100% correct in pointing to the Weaverbird soft wing junk sail. And the SJR is indeed not so tolerant of sloppy helmsmanship – mine isn't anyway - and I should know as I am not much of a helmsman.

The testing a few years ago did seem to suggest that the best performer with the best alpha tolerance might be the soft wingsail, and balance-wise the Weaverbird planform would undoubtedly be the closest match to the hoped-for Ljungstrom rig, possibly the only one which could really fit that mast position – and quite possibly the best performing junk sail.

The only reason the soft wing sail was left out of the discussion was because Karl was talking at the time about wanting to get set up as quickly as possible, with the simplest solution, should the Ljungstrom sail not meet expectations.

However, for someone with the technical skills and ingenuity that Karl has shown, a Weaverbird sail could well be the shot – what about it Karl?  It would be the first such sail “down under” and we need to do something a bit more impressive on behalf of the junkies, than recent performances at the “Tall Ships”! (The four of us took the last four places - strictly speaking, all DNF).

I still come back to Karl's experiment and the subject of this thread. It is all very well dismissing the "two leading edges" proposition - and it is doubtful - but where is the plausible explanation for the experimental result? The answer may be in the paper David refers to. That's a bit above my ability to really comprehend so I don't know. It did seem though, from the little bit of the experiment actually shown in the video, that those tell tales were flying quite nicely and maybe the jibs really were helping there. I have never really thought the so-called "slot effect" had much to do with the SJR, but maybe it does a bit.

Karl's experiment does not demonstrate what I always thought might be an advantage of SJR and that is the entry shape of the foil - never crushed and always much less interfered with by the mast, compared with the contiguous sail. The key to the SJR jib is that you can make a really good entry shape for the foil. That's where the soft wing stands out also, maybe even better.

Balance wise, the weaverbird sail would probably be the best fit to that mast position and underwater profile, and the SJR probably the worst. (A little mizzen sail would fix that problem though).

Cheers Graeme and before I move on to my answer, I'd like to acknowledge all the emails you have sent me with advise and answers to my questions over the last week or two and while I'm thanking people, Arne has also been of great help to me and tried to steer me towards the light but I can be a bit stubborn and for that matter, Paul Thompson and I go back a long way as friends and has been a great help and may even build my next sail. I helmed Paul's La Chica to a win over Zebedee a few years ago and after that day, seeing the highs and lows people experienced, you can't tell me Junk Riggers don't like going fast, as long as it's fun of course!

 Yes Graeme, I actually had way too much footage of the tests and was a bit overwhelmed by it all along with trying to build a yacht so I decided to pretty much voice over some of the content and yes, I would have made the video differently for the JRA audience  but it was mainly aimed at my yacht build community on YouTube who I think have experienced a bit of a roller coaster ride (tell me about it) as I go back and forth between the Ljungstrom and a Junk Rig. What did surprise me was how many are supportable of me going to a Junk Rig and I get the feeling there are a growing number of people interested in what a Junk Rig can offer.

"I do find this improvised, low-tech type of testing very interesting, and believe much can be learned from it. Well done."

I do to and it probably wouldn't surprise you to know I've done a lot of comparative tests during the build! I even designed and built my own hygrometer (Paulownia timber moves a huge amount with small humidity changes) and before I built it, I didn't even know the word. It was useful and worked great!