There's little more to say on this exhausted (exhausting?) topic, except that 'fragile' and 'robust' do not automatically equate with 'split' and 'unsplit'. They are words that are more about materials and construction than planform. Clearly, the sails for decorous day-sailors, coastal cruisers, epic explorers, red-hot racers and robust round-the-Horners are, and ought to be, built in different ways.

What's a better word? 'Vulnerabilities', perhaps. Rigs of all types have their vulnerable spots that need to be recognised and addressed.

Len wrote: I just thought it odd that there seems to have been an idea that the SJR was more fragile when it would seem that it should actually be more robust.

(The one small advantage we have down here in NZ is being able to get the first word in, so once again...) I would hesitate to say that the SJR is more fragile - or that it is more robust.

The possibility of fragility in relation to the SJR has been raised on these forums and discussed often enough that it has almost reached the point where fragility is beginning to be accepted as some sort of fact, as Len seems to be wondering in the highlighted passage above.

The question arises from the proposition that no-one as yet has subjected a SJR to a long ocean voyage, including, say, 1000 miles on end, reefed and strapped down for a long hard passage to windward etc etc. Its a fair question, and until that has been done, we can only speculate about its robustness under extreme off-shore or heavy-duty-use conditions. 

Some of the stresses on a low yard-angle, high balance rig (such as the SJR) are indeed less than on a contiguous, “conventional” or high-peaked, low balance cambered junk sail, and the panels of a SJR are smaller, as you say Len. But I don’t really think too much can be made of that.  All of the junk variants carry less stresses or loadings in their canvas and running rigging than, say, the sails on the well-proven and well-understood bermudan rig. 

From the point of view of robustness of the sail itself, the main difference between the SJ sail and other junk sails is the jib panels, which have a leech which can never be stretched tight and in fact never subjected to much tension at all. This may be a point in their favour, but it has been surmised recently that it could just as well be a weakness if they were allowed to flog – somewhat (but not quite) the same as a bermuda-type jib should it be allowed to flog. I can't speak from experience here, but take a guess that a sail built with rope or heavy webbing on all four sides in the manner recommended by Arne might well prove to be the most robust of all. This very strong type of reinforcing would not really suit a split junk sail, in particular its stack of jibs, however, so perhaps a SJR would not be able to match a stoutly built Johanna-type sail, for robustness (which, by the way, is not quite the same thing as longevity).

No inherent weaknesses have been reported with SJR sails to date, after a number of years now. As we are now seeing an increasing number of these rigs, if there is any structural weakness then sooner or later I suppose we will find out. Personally, I think it is a red herring but I have no doubt it will be raised yet again on this forum - and who knows – perhaps under severe ocean sailing conditions a SJR will one day be found with its jibs somewhat the worse for wear. If so, it wouldn't be the first junk-rigged boat to reach port after a hard passage, with a sail in need of repairs. It is not a bad thing to be aware of the possibility, and if it so transpires, then I suppose there will be a lesson learned in how to repair the damage, and in how to build the weak part (if there is one) a little stronger next time.

I have no idea if a SJR is over-all better than any of the other contemporary junk rigs. Some comparative testing has been done, but not enough to say very much one way or the other. I expect the different contemporary junk rigs all have their small advantages and disadvantages. All I know is that the rig does work pretty well, and my next one is going to be another SJR. Anyone attempting a long ocean voyage or a circumnavigation with a SJR should be aware that they might be the first person to do so, and if it turns out that there is some hidden fragility in the rig which we don’t know about, then that person will be the first to discover it. A nice challenge if you ask me – an opportunity for notoriety, but perhaps better for someone who knows from prior experience what extended voyaging entails.

I think it is fair to suggest that a first-time ocean mariner ought perhaps to be a little cautious about also being the first person to embark on an extended ocean passage with their own home-made SJR – but I will get the first word in and say: that small caveat is about as far as it ought to go, and  a very long way from accepting "...the idea that the SJR [is] more fragile..."

Then I see this wing (ignore the pint size jib). The big round pole in the middle must mess with the air flow. It seems that middle pole/mast moves from side to side to help change the wing shape for tacking. Now the wing is higher AR than most junk rigs, but that is about it (Video shows a bit more). These things can go somewhere around 4 times the wind speed because the hull to water interface has much less drag (static drag). I would think though that if they could go even faster by getting rid of that lump they would. Compared to these, all conventional boats are barges. But the sail smoothness seems to be one of the lesser concerns.

Len Ovens wrote - “You have sparked another dumb question in my mind. How "attached" is the air flow anyway? Is that a good thing?”

No Len, it is not a dumb question. In practice it could be the the answer to a lot of the questions being asked in this thread.

In conversations with world class glider pilots I have learned that they get upset if you put your hands on the leading edges of their wings as you will leave greasy fingerprints, and that could ruin their performance. Apparently they are first aware of rain when the first drop of water hits the leading edge and a vibration due to upset flow can be felt through the airframe. As for bugs contaminating the wings, wow! This suggests that they are working with boundary layers only millimetres thick. With rough material sailcloth, seams and the such like on a junk rig we can at best be thinking in terms of boundary layers some centimetres thick, or worse. So how does that effect us?

Arne is right when he says that I concentrate on the camber at the leading edge, and if I can get a good attached flow over the first section of the rig it will help give good performance. When the luff telltales fitted some 20 to 30 cm back stream cleanly then the boundary layer there must be fairly thin, the the leading edge working well, and the performance is good.

With the lower sail balance on the non-split cambered sail things are somewhat different. In the past there has been talk of the good tack and bad tack issue. With the rig set on the port side of the mast and on starboard tack the camber can set smoothly but the full drag of the mast must be added to give the overall performance. On port tack the cambered surface may be distorted by the mast but the mast drag may be significantly reduced then the overall performance may be just as good. There are reports of the 'bad tack' being better than the 'good tack' so perhaps we should look more closely at this situation.

Could it be that Len's comment about 'attached' flow has an answer? The boundary layer must thicken very quickly with the rough surface and many irregularities of the junk rig, but that does not necessarily say that the rig is stalled and losing the large part of its lift. When Arne sails with the leech telltales streaming then the rig is clearly not stalled since a cambered foil stalls as the separation bubble comes forward from the trailing edge. Could it be that a thick boundary layer keeps the overall flow attached and lets Arne's rig keep good flow over the full surface of the rig, despite the 'contamination' of the mast near the luff? It's a difficult one to understand, and would require much effort and time to research, but it would appear that we can look differently at the split and non split cambered rigs.

Having been fortunate to have sailed on Johanna a couple of times it is not possible to say which gives the best performance. Only by building two rigs and fitting to identical hulls and sailing them together would we find the answer. Even then we would still have to evaluate the different physical characteristics.

Until we do that then we will always be asking the question, to split or not to split. Perhaps we should concentrate more on mast position or ease of handling when selecting a rig.

Cheers, Slieve.

David,
You surely are right there. I don’t expect to perform that well to windward, offshore. That is badly uncomfortable, anyway, so better avoid it if one can ( yes, even I have tried it...). Besides, the shape (and size) of the vessel plays a bigger role for going to windward, offshore.

Still, on our sheltered fjords, the fetch may be up to 10-15 miles on places, and a very steep, short chop may build up rapidly. This chop can stop a small boat dead. Again, the hull shape is as critical as the sail.

Ingeborg, with her slim lines and large, heavy keel, is well suited for these conditions. In addition, the ‘groove’ of my sail seems to be just as wide as on a Bermudian sloop, so it doesn’t  add to the problems.

Arne

PS: I have no idea of how the airstream can re-attach on the leeside of my cambered panel junksails, on port tack, but the telltales at the leech anyway say that it does.