David Doran wrote:I wonder if by leaving the battens longer than required during initial set-up, you could move the jiblets further forward or the main panels back a little if required.Would it give a little leeway for minor adjustment of sail balance in case the calculations are slightly out before cutting the battens to the final length and the sail its final fixed position.  

Both these solutions would be at the cost (?) of widening the gap between jiblets and main. I've not heard Slieve say much about this gap, though he did say that the gap on Poppy could usefully be reduced from 330mm to 200mm.

It might be interesting to do the experiment to see what effect this change would have.

Chris

Correct - the sail is split at the position of he mast.

Any fore-and-aft movement would change this, so the sail is restrained to prevent it.

Chris

I seem to remember Paul was advocating no more than 25% balance on the Aero Junk rig, but Slieve has planned to push the balance of the split rig to 36% in the past I believe. The current balance on Amiina is around 33% , and my split rig (currently under construction) will have 31%.

Chris

Hi Scott,

a number of factors are involved in the questions you raise. As David Tyler said the maximum balance within the sail is around 25%. Being able to adjust the balance while sailing is unnecessary in split and aero junk sails because of the relatively large balance percentage. In high aspect ratio sails with a reasonable amount of balance it is also unnecessary, if there is little balance then it could be an advantage when sailing off the wind, but probably not essential, as the sail center of effort is closer to the mast than with a low aspect sail. With low aspect ratio rigs with a small percentage of balance, however, it is a big help to have the balance adjustable in order to reduce the amount of weather helm when sailing off the wind. I hope that clarifies the situation.

David.

 "why not balance the sail as much as possible?"

Fair enough - but as much as possible is in fact with the mast at about 25% of chord, and if you go for much more than this, there is a danger of the sail over-balancing and "snatching" to a greater angle of incidence - remember that the actual centre of effort when sailing to windward is not in the same place as the centre of area, but is further forward. 

When sailing off the wind, the sail is not acting as an airfoil, and then the centre of effort is in the same place as the centre of area. So you can swing the sail further forward on the mast, when off the wind, but this is by no means obligatory, or even commonly practiced. It helps with a low aspect rig, when the centre of effort would be far out to one side; but on a high aspect rig, it is not really necessary and the control lines can be much simpler if the sail is kept in one position on the mast.