Hi Paul

Hard luck on the back problem. Of all the useless cures that I have heard of, whisky is the nicest, so I suggest you try that. Take it easy and don’t push it as you have only one back.

Hi Mark

You rise a number of interesting points. When I started to draw up a more balanced rig I realised that the symmetrical cambered NACA 00 series foil section balanced at about 25%, and that a flat plate balanced about 33% aft of the leading edge. This left me struggling to imagine how much balance I could use and still have a stable rig with my planned sail shape. The Poppy figures can be worked from the published drawings, and Amiina was pushed to a 33% jib/ total area ratio after contact with Roger Stollery and the model sailing world, in the quest for light sheet loading.

I see this as a limiting situation which depends on all other elements which can effect balance being correct. When you suggest that the Luff on Paul’s boat can become slack when compared with the leech then my initial reaction is the word ‘Ouch!’ For a high L/D ratio and therefore the centre of pressure in the correct position the luff must be tight. This is not negotiable.

Yes, my battens are stiff in all directions, so a downhaul in line with the mast tensions both the luff and leech, with the luff being tighter than the leech.

You suggest, "It has a lot of potential and in theory should out perform the Split-junk." Em, which theory is that? I find it hard to believe that a pointy rig shape with its associated vortex/ induced drag could outperform a rig with a better tip shape. Why are all the faster Bermudan rigs squaring the heads of their mainsails, and the fastest windsurfers using an upswept sail head? The airliner designers would not be spending so much on tip design if it was not vitally important. This is something we do not know that much about, but cannot ignore.

Cheers, Slieve.

Hi Guys, sorry but I’ve been busy and have just found this thread. It would appear that there may be a little misunderstanding running about which may be leading to some slight embarrassment.

The ‘balance’ problem is not unique to the split rigs. Every air and hydrofoil has a centre of pressure which will move around depending on the angle of attack, and if the centre of pressure gets too close to the pivot point then there is the risk that the foil will flip, or at least will not feather when released. On the other hand there can be advantages in getting the centre of pressure with a balanced rig near the pivot in that it will produce light sheeting loads and possibly reduced unwanted sail twist and creases.

Problems arise when naval architects try to balance a sailing vessel, as they do not know where the centre of pressure of a sail is actually acting. The normal procedure is to calculate the centre of area position of a sail and guestimate an amount of ‘lead’ to allow. With experience this has produced adequate results over the years with standard designs, but starts to fall down when applied to design ideas which are ‘novel’. The balance of the split rigs tends to fall into the novel grouping.

The figures I have used for split junks are no accident and are the result of attempting to envisage what is actually happening in each section of the rig at each stage of reef, and have been modified after the first effort in Poppy as more information had been received. The model sailing world has been helpful here, suggesting that the maximum stable ratio for jib to total area would be 33.3%, but this is possible with virtually no split between the jib leech and the mast. This is also dependent on the sheeting angle of the jib and camber shape of the mainsail, so cannot be applied as a simple ratio. As with all balancing acts it is not only the force and its direction that has to be considered, but also the moment arm, and this would appear to have raised a question with Amiina.

This rig was drawn to be very close to the limit, and it could be that it has slipped too close to the limit with it’s recent set up. The increased ‘split’ moved the jib forces further forward, but the slackness in the main panels may have changed the ‘main’ force with increased drag, which would also have an effect. Edward is waiting for a report from me on the rig as both of us know that we are not getting full potential performance form the present set up.

The situation with Paul’s AeroJunk Rig is not clear as I do not have all the information. Simply reducing the area of the jibs may not necessarily be the best solution, as the moment arm forward may not be reducing with the area. There is even a risk that decreasing the area may even increase the jib force and its effect on the rig balance. Equally, the effective sheeting angle and the mainsail camber could also be causing problems. I will admit that I don’t understand the theory that a larger rectangular slot will produce a greater jib efficiency.

Regardless of the balance problems, it seems that Paul is getting useful performance from his rig which is good news. Keep up the good work.

Cheers, Slieve