I'm not sure if Slieve is following the forums all the time, if he doesn't chime in, then have an off-line chat with him about this, because what you seem to be saying sounds very consistent with some of the trials they did on Amiina's first sail, when developing the Mk ll sail. You might well be on the right track, with combined single top panel and longer yard. In addition to the new jibs.

As weird as it seems, I made an interesting experiment during the weekend sail.

With a full day of strong headwinds I decided for whatever reason to reef away the topmost panel with temporary lashings (see photo). Later I also took off the sheetlet from the now new yard.

And what happened? Well, the pointing ability was significantly improved. Not so much as to make me forget about making larger jibs during the winter, but anyway.

The explanation? Only guesses here, but maybe the original top panel is too weak drivewise and mostly adds to heeling and not forward thrust in headwinds. 

I might make a new top panel along with new jibs. I think I will take 2 original panels off and make only one that is slightly smaller than the two together, and with ample camber plus a lower yard angle than the original top panel.

Jamie, you wrote, 'The part of the jib camber shape and the arc of a circle -idea is something I can’t understand, though. Could you shine more light on this? '

Em? I'll try. I can list the problems, but am still looking for the answer.

Overall from jib luff to main leech the rig is an airfoil. The desired shape for a foil, even only one canvas thick is fairly well known, with a rise angle, maximum camber point between 30 and 40 % chord and ending in a straight run to to the leech. When you split the foil, with jibs and main then there is twice the problem in deciding each foil shape separately and how they combine to make a combined foil. Experience from Bermudan rigs is a great help here, but, and this is the problem, but the angled shelf foot jib panels in the SJR cannot be tensioned down the leech so will sag away, and effectively change the shape of the resultant airfoil.

Initially I built the jibs using a typical Bermudan jib shape, and as expected the leech fell away in the middle so that the shape of the leech when viewed from the rear was a fairly smooth curve and not be what was wanted (which was Graeme's tin-plate shape). Still I had to start somewhere. Many experiments were tried with mini sheetlets pulling the middle bit of the leech either aft or towards the battens with mixer results. The Mk2 Amiina rig has batten pockets included to see if the shape could be forced closer to the shape we thought would be best. A lot has been learned, and the jibs were modified before the original draft notes on the rig were written, and a correction was included which helped. As ever, simplicity is a key issue, and I have been wondering if a good/ adequate shape would result from a camber drawn as a simple arc of a circle. Easy for the builder, it would be only after making a model or two, as I did for the first rig that it might be able to see how it would look. At a guess it might require a slight (1 deg) increase in sheeting angle.

Having retired from sailing I'm not rushing to start more experiments, so I'm afraid this is only theory.

As for the Galion 22, until more is known I would suggest sticking to the early section with modifications as it is known to work.

Does this help, Jami? (Oops! I've just realised that in the past I may have spelt you name with an 'e' on the end. Sorry. Jamie is the name of my most troublesome grandson).

Cheers, Slieve.

Slieve thanks,

I really appreciate your insight.

This is fully in line with my vague thoughts - it’s not worth it making new jibs unless the change compared to the existing ones is big enough. I was thinking maybe 1000mm chord, but 1100 is probably better to go for - the effort is essentially the same.

If I sew new jibs, and get what we want from them,  this missed shot with too small jibs has at least proved the theory of the essential SJR jib size in practice. Maybe it will help others in this community.

The part of the jib camber shape and the arc of a circle -idea is something I can’t understand, though. Could you shine more light on this?

Me too. In the meantime, here’s a little bit more food for thought:

Jamie wrote: …should I make new jibs. I might need 30cm extra on the luff in order to make any real change worth the effort. And this might turn the boat into a lee-helm monster…

Now you are talking about a different issue -just to keep the terminology clear: a change in the nature of the sail, or its placement, may affect helm balance. Whether the boat has lee helm or weather helm etc.

Wheras, the previous discussion was about the dynamic balance of the sail – sail balance – the ability of the sail itself to rotate and “weathercock” when the sheets are let fly.

Helm balance is affected by a lot of things, CLR and CoE (which are static, geometric points) are a guide but not the whole story. On a small boat like yours, trim and angle of heel are likely to affect the helm, and also provide ways of balancing the helm. My little boat has a little lee hem in light conditions, but as wind increases and angle of heel increases, weather helm develops and becomes increasingly heavy – if I don’t reduce sail it eventually becomes quite “hard nosed”. This is not unusual, and for me is acceptable. It is something which depends quite a lot on hull shape. I have found shifting my weight, moving forward or aft in the cockpit, greatly mitigates these effects. My Pelorus has heavy weather helm when pressed hard - and I can mitigate that by reducing the area of the stay sail (which, theoretically, moves the C of E aft. Think about that for a moment). The point being, helm balance is not just a simple matter of balancing a couple of geometric centres on a sail plan drawing. (How much "lead" of CoE over CLR - that's the real question, and it seems to be a bit of a magic art !)  It is a great deal to do with the shape of the hull, not just its lateral profile. And rudder too. (I'm sure your improved rudder will be an asset in any case).

Making new jibs, shifting the luff forward 30cm and extending the battens accordingly will move the so-called Centre of Effort (actually the geometric centre of the sail) forward 15cm if nothing else is changed. I would be interested in the comments of people like David, Slieve or Arne who know more about these things than I do – on what would be effectively shifting the rig forward by 15cm.

Making the jibs more powerful – now, this is something that needs a little thought, and maybe Slieve’s knowledge of aerodynamics might help here. If the jibs on a SJR are made more powerful, would this result in the actual centre of effort of the sail moving forward? Maybe it is more important to consider that, than the relatively minor effect of effectively shifting the rig forward by 15cm.

(It’s a pity you can’t really make adjustments to mast rake, which is a convenient way of tuning the helm in some cases. One of the few small disadvantages of Slieve's SJR design, with its “self-draping” sail geometry, is that you are pretty much stuck with a zero-rake mast.)

I still think that in a small boat there are so many factors that can affect helm balance, my gut feeling is, making new jibs would not turn the boat into a “lee helm monster” – unless it already has lee helm. Anyway, you know your own boat, its probably a judgement call only you can make, after getting good advice from Slieve.

...I'd rather ... find me a cheap Albin Vega... Well, I'd rather consider a ittle riding sail, if the worst came to the worst. I don't think it will, and I don't think it would be necessary to shift the mast for the sake of 15cm. I'll say one thing though, since adjusting mast rake is not a practical option with SJR of the type designed and rigged  by Slieve -  if I were building a split junk from scratch (which in fact I am) I will make elongated partners and allow for a little movement fore and aft of the mast position which would not involve major structural changes,  should that later prove necessary.