I hope that once Slieve finishes his project, the ratio will improve significantly!

Really looking forward to that! 

Slieve, let us know if you need any help or support.

Once again discussions and experiments on the various rigs come down to the personal opinion of various club members. We have no practical testing system to answer the many questions. In the long run it s not necessarily out and out performance that dictates which rig to use, but more often some practical consideration, or some biased opinion expressed by a club member. We are all fickle.

Mast height, mast location, repairability in remote places, rudder performance, simplicity, KISS, and many other considerations may push the boat owner in one direction or the other. The question, “If I build this rig will I regret not having built that one?” will always be in the back of anyone’s mind.

Karl’s experiments are interesting, and must have helped him weigh up the pros and cons. They have certainly been of interest to all of us.

It was easy for me as I was prepared to go out on a limb with the SJR and its special requirements, and wanted to test my theories based on a lifetime in sailing and aviation. I was more than happy with the result as I felt I had the best performing and easiest to sail cruising rig, and in the end wasn’t happy sailing anything other than a SJR. But as I say, please remember that I’m biased.

Cheers, Slieve.

Anonymous wrote:

From time to time, I am being told that the 70° yard I rig on my sails leads to higher induced drag than with a flatter top. If that is the case, it cannot increase the drag angle with more than 1-3°, at most, or my boasts would have struggled with pointing with the boats around me.

In 2020, on Slieve’s request, I fitted 2-metre long telltales to the leech of the two upper panels of Ingeborg’s sail. These turned out to not show any sign of a swirl going on up there. I took a little video of them and now I just replayed it. The ‘longtails’ stood right out like on the photo, and only when I stalled the sail, did they disappear behind it. The ribbon flying from the yard’s extension stick, also just showed the wind, and did not even react when the sail was stalled.

Another proof that this sail doesn’t do as it is being told...

Cheers, Arne

(Photo album section 8-22)

Wow, what a great way to test what's theoretically going on and it looks like the top of your sail is earning it's keep! Do you have any profile pictures so it can be seen how horizontal the top telltales are compared to the bottom ones?

Having a look at it, I would suggest one change though, include some short telltales as well because the tail of the ones you have shown could almost be pulling the telltale straight? Not that it really appears that way and it's the middle ones that look like they might be in a little more turbulent air , to my eye.

I would be interested in your thoughts Arne but if that was my Bermudan Square Top Main I would be thinking of allowing a little more twist in the top of the sail so like lower down the air exit is a little more in line with the exit angle of the sail panel? But what I'm observing might not match the reality of what's going on and you might have already worked out what suits your sail best? Certainty if you wanted to de-power the top of the sail you might allow more twist, or simply ease the halyard...

David Tyler Wrote:

I sympathise with Graeme in his frustration. While it’s interesting to go down these rabbit holes, this topic asks whether Karl’s test shows anything useful and if so, what; and if not, what would, to help him to decide what form of JR to build, and whether it’s worth moving the mast.

  
as Slieve has said, the top of the sail is very important. Just as important as little camber changes, as the tip vortex contributes hugely to the overall drag. This is why Bermudan sailors are going to square top mainsails - the pointy top is the worst possible planform. This applies to the Johanna high peaked yard as well. Arne compensates by piling on more area; whereas Slieve goes for a yard at 30 degrees to horizontal and I go for 45 degrees as the lowest possible on my wingsail. We aim to minimise the adverse effects of the tip vortex and get the most efficiency from the least sail area.

So if Karl wishes to build and test more models, perhaps he might do, in miniature, what Arne wishes for. Three models of complete sails, of exactly the same area, on the same hull, mast length optional. 1) a SJR with proportions decided by experienced SJR users, not by those of us who know the theory but not the practice. 2) a Johanna sail, designed by Arne for this particular boat 3) a Weaverbird wingsail. 
Of course, that brings more problems with it because the air moves faster and at different angle at the top of the sail than lower down, and a single fan must be delivering a spiralling airstream. Not a simple experiment any more. 

Thanks for the suggestion. I agree that the top of the sail and tip vortex are important and that optimising the head shape could improve the performance of any Junk Rig.

However, that wasn't the purpose of my experiment. I wasn't trying to find the ultimate Junk Rig design or compare every variation. My aim was simply to compare a Split Junk Rig with the more common Contiguous Junk Rig, while keeping the comparison as fair as practical.

The Weaverbird is still fundamentally a variation of the contiguous single-sail concept. What I wanted to investigate was whether splitting the sail into two interacting sails offered an aerodynamic advantage over a single sail.

The Split Junk Rig appeared to consistently show a higher 'lift to drag'' ratio, which is consistent with published aerodynamic studies on two interacting sails. That was the question I set out to answer, so I don't plan to build another series of models. I'd rather put what I've learned into the full-size boat if practical and only if my 'overcooked' version of the  Ljungstrom proves unpalatable.

I sympathise with Graeme in his frustration. While it’s interesting to go down these rabbit holes, this topic asks whether Karl’s test shows anything useful and if so, what; and if not, what would, to help him to decide what form of JR to build, and whether it’s worth moving the mast.

  
as Slieve has said, the top of the sail is very important. Just as important as little camber changes, as the tip vortex contributes hugely to the overall drag. This is why Bermudan sailors are going to square top mainsails - the pointy top is the worst possible planform. This applies to the Johanna high peaked yard as well. Arne compensates by piling on more area; whereas Slieve goes for a yard at 30 degrees to horizontal and I go for 45 degrees as the lowest possible on my wingsail. We aim to minimise the adverse effects of the tip vortex and get the most efficiency from the least sail area.

So if Karl wishes to build and test more models, perhaps he might do, in miniature, what Arne wishes for. Three models of complete sails, of exactly the same area, on the same hull, mast length optional. 1) a SJR with proportions decided by experienced SJR users, not by those of us who know the theory but not the practice. 2) a Johanna sail, designed by Arne for this particular boat 3) a Weaverbird wingsail. 
Of course, that brings more problems with it because the air moves faster and at different angle at the top of the sail than lower down, and a single fan must be delivering a spiralling airstream. Not a simple experiment any more.