Sail Balance - Position Relative to Mast

  • 16 May 2017 09:51
    Reply # 4835750 on 4835722
    David Doran wrote:

    I was wondering also if it might be possible to effect minor fore-aft adjustment of the mast angle by using different wedges in the through-deck hole.

    Has anyone ever tried or done that with the mast? 

    Roger Scott is doing a variation on the them, at the base of the mast.  He wasn't quite sure how much rake to put in his mast, so has some sort of wedge and roller arrangement to adjust it.  I shall see it this weekend and I'll try and get him to post about it.
  • 16 May 2017 09:13
    Reply # 4835744 on 4835722
    Anonymous
    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


  • 16 May 2017 08:56
    Reply # 4835722 on 4793670

    "As I understand it, once the calculations are done and the split rig is in place there is no scope for later fore-and-aft adjustment of the sail (or alteration of mast rake) is that correct?"


    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.  

    I was wondering also if it might be possible to effect minor fore-aft adjustment of the mast angle by using different wedges in the through-deck hole.

    Has anyone ever tried or done that with the mast? 

  • 16 May 2017 07:50
    Reply # 4835646 on 4793670
    Anonymous

    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

  • 15 May 2017 22:53
    Reply # 4835171 on 4809000
    Chris Gallienne wrote:

    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

    As I understand it, once the calculations are done and the split rig is in place there is no scope for later fore-and-aft adjustment of the sail (or alteration of mast rake) is that correct?
  • 02 May 2017 17:55
    Reply # 4809000 on 4793670
    Anonymous

    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

    Last modified: 02 May 2017 18:48 | Anonymous
  • 02 May 2017 14:40
    Reply # 4798284 on 4793670

    Thank you Chris, and David. This has absolutely helped clarify my understanding.

    I have one more question that I hope is my last on this subject. In a split junk rig or areo junk rig is 25% balance still the practical maximum or do these rigs allow for more sail area in front of the mast somehow?

    Scott.


    Last modified: 02 May 2017 14:50 | Anonymous member
  • 02 May 2017 10:25
    Reply # 4795567 on 4793670

    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.

  • 01 May 2017 16:25
    Reply # 4793790 on 4793778
    Anonymous
    David Tyler wrote: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 

    With China Girl, the result of this is that when tacking she will fail to come through the wind, and falls away on the old tack. I have to remember to ease the sail back on the mast when sailing on the wind.

    Chris

  • 01 May 2017 16:13
    Reply # 4793778 on 4793670

     "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.

       " ...there is nothing - absolutely nothing - half so much worth doing as simply messing about in junk-rigged boats" 
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