Sail Balance - Position Relative to Mast

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  • 12 Oct 2018 15:11
    Reply # 6719362 on 4793670

    Hi--See jpg below. I just did a check in QCAD comparing the chord-wise balance computation and the area-wise balance computation for the parallelograms and got no difference (unless the 5th decimal place is of importance).

    Perhaps a minor point but I've also found the centroids or center of area of each of the individual panels and found that the balance of the 2 highest fan-shaped panels, taken together, has a 24% balance versus the lower 5 panels which have 33% balance. 24% being more inline with conservative thought....meaning that as you reef the balance of a similarly-shaped split rig decreases.

    On the issue of speed of weathercocking I've found, even in the F3-F4 wind regime that I've had to reef, that gybes ends with much more of a "bang" then the full sail gybe in F1-F2. My explanation is that the 3:1 sheeting mechanical advantage doesn't change when reefed and becomes a 3:1 frictional 'disadvantage' that stops the sail abruptly (bends battens?). I'm wondering if the bang would be even louder if I had substantially less balance, say in the 10% range, resulting in an even greater speed of weathercocking? Forced to wear ship?

    robert self

    Last modified: 12 Oct 2018 15:58 | Anonymous member
  • 12 Oct 2018 10:18
    Reply # 6719175 on 4793670

    Just a point I'd like to make about when talking about balance.  

    When talking about balance in front of the mast,  I think that it is important that the posters clarify whether they are talking about "sail area" in front of the mast, or "chord length".  

    When I made the Split Junk Rig for the Wayfarer, I both misread Slieve's files and in reading discussions on the forum, got it into my head that there was 33% sail area in front of the mast plus the split and built the jiblets accordingly. This would have resulted in my sail then having the luff of the jiblets approx 40% of the chord length in front of the mast.  

    Luckily before I set sail, some postings earlier in this thread , warned that this was wrong and more likely correct that the leading edge of the jiblets should be no more 33% ahead of the mast.  So, not wanting to face building a complete new set of jiblets I cut a bit off the trailing edge of the jiblets, ending up with 29% sail area in front of the mast, but still 35% or so of chord length because of the split. 

    The sail does feather with this amount of sail area and chord length, but it is slower to feather than I like.  So I intend build another set of jiblets to reduce the amount of sail area in front of the mast to 25% plus the split.

    If the Weaverbird rig has 25% sail area in front of the mast and the Split Junk or Aerojunk has 25% sail area in front of the mast, I think the actual balancing effect would be different due to the split and thus increased chord length.     

    So, in the interests of clarity and help in ending confusion among us newbies, I think it is important to clarify whether you are talking about actual "sail area" in front of the mast, or "chord length and sail area" in front of the mast.  


    regards, Dave D


     

    Last modified: 12 Oct 2018 10:20 | Anonymous member
  • 12 Oct 2018 01:21
    Reply # 6718834 on 6717559
    David Tyler wrote: Slieve,
    With respect, I do wish that you could banish this particular bee from your bonnet. I am going to hold very firmly to my position that I should not wish to go to sea with a junk rig with a balance area much in excess of 20%. I am going to continue to advocate, based on practical junk rig experience over many years and many miles, moderation in the article of balance area. The greater the balance area, the greater the issues that I have encountered with ill-behaved sails.
    LC had 22% balance in her foresail and had no problems of any sort due to balance. In fact the sail set perfectly and handled very well.
  • 11 Oct 2018 16:15
    Reply # 6717938 on 4793670
    Anonymous member (Administrator)

    ..drifting limits...

    I guess my attitude to what the maximum balance in a one-ply JR should be, has drifted a bit over the years. In the early days of my cambered panel sails, I aimed for only 10% balance to minimise distortion of the camber on one tack. Fine in theory. Then Paul Thomson rigged his La Chica with 18 and 20% (?) balance, and got away with it. I still don’t dare to recommend a cambered panel sail with 25, 30 or 35% balance to others, and that is for one reason: I haven’t sailed with this much balance myself. I may well try such a hi-balance cambered sail, if I get access to a dinghy. If it turns out good, I will recommend it, but only then. I guess I am conservative...

    However, by adding a split in the sail ( see Slieve’s SJR), the equation will change, to allow much more balance (ask Slieve how much).

    Anyway, I wonder if we are discussing a not-problem here: As far as I remember, Christopher had no need for more than 20% balance.

    Arne

    Ps: A while ago I made the diagram below to help me find a what yard angle will match different amount of balance. As a result, if I were to set the sail with 20% balance, I would design it with a 65° yard.

    (PPS: Only now did I spot Asmat’s warning against 28% balance...)


    Last modified: 11 Oct 2018 16:38 | Anonymous member (Administrator)
  • 11 Oct 2018 16:07
    Reply # 6717917 on 4793670

    Wylo 32 schooner Branwen's foresail has a balance of about 28% chord at the  foot, reducing to about 20% at the throat. (My foremast leans forward while the sail's luff is vertical). The sail is well behaved, showing no tendency to instability and the battens are stiff enough to resist S bending.

    The sail has about 8% camber, with the deepest camber situated at 35% abaft the luff, so that with the mast to leeward, a bag forms in the sail ahead of the mast. I now think this is detrimental to windward performance. I find that she goes better with the mast to weather, which is the opposite of what's expected. A flat sail might not suffer from this defect.

    Asmat

  • 11 Oct 2018 13:40
    Reply # 6717636 on 4793670

    David, who has a bee in his bonnet?

    The fact that you 'should not wish to go to sea with a junk rig with balance area much in excess of 20%' is simply your opinion, and is not ' getting towards the top end of the range' as you quoted earlier. The fact that you hold this restricted opinion is up to you, but should not be used to mislead those who wish to look further and may be prepared to examine the full range of possibilities.

    The figures I have quoted have all come from successful and stable rigs, one of which, I am informed, recently spent 3 days riding out a prolonged gale with no adverse effects.

    For those who might be interested, in his book 'Design and Build your own Junk Rig' first published over 25 years ago, Derek van Loan described rigs he first designed in the '60's. The basic flat rig he suggested has 25% chord balance.

    So let me repeat – 'Readers are advised to try to determine what is opinion and what is tested and proven fact over the 'full' range of possible answers.' Do not be mislead by the 'experts.'

    Cheers, Slieve.


  • 11 Oct 2018 12:24
    Reply # 6717559 on 6717485
    Anonymous wrote:

    In post #6714642I Christopher Phillips wrote, “I have had to give the main a balance of 20% chord, which makes for about 17% area.”

    In reply in post #6714919 David Tyler wrote, “20% balance is getting towards the top end of the range, but shouldn't overbalance and snatch, I don't think.”

    It is wrong to mislead the readers by making statements about things that you have no personal experience of, and are only guessing at. 

    Cheers, Slieve.

    Slieve,
    With respect, I do wish that you could banish this particular bee from your bonnet. I am going to hold very firmly to my position that I should not wish to go to sea with a junk rig with a balance area much in excess of 20%. I am going to continue to advocate, based on practical junk rig experience over many years and many miles, moderation in the article of balance area. The greater the balance area, the greater the issues that I have encountered with ill-behaved sails.
  • 11 Oct 2018 10:56
    Reply # 6717485 on 4793670

    In post #6714642I Christopher Phillips wrote, “I have had to give the main a balance of 20% chord, which makes for about 17% area.”

    In reply in post #6714919 David Tyler wrote, “20% balance is getting towards the top end of the range, but shouldn't overbalance and snatch, I don't think.”

    This is typical of the 'miss information' or 'false news' which is being posted on the JRA website, and which can discourage members from experimenting and making advances in rig design.

    Junk rigs have been sailing successfully and efficiently for a number of years with chord balance of up and including 35% with absolutely no sign of instability nor overbalance, and there are thousands of model yachts with balanced rigs which use 33% area as their design criteria for rig balance.

    The streamlined symmetrical NACA 00 series foil sections do have a centre of pressure at about 24% chord, so it is possible that flat and therefore basically symmetrical rig may have similar figures, but it has been fully tested and proven that cambered soft rigs are fully stable with 33% area in front of the mast/ pivot point, provided that there is not a significant gap or extended moment arm.

    It is wrong to mislead the readers by making statements about things that you have no personal experience of, and are only guessing at. There are too many instances on the JRA website of opinions being misrepresented as facts, so readers are advised to try to determine what is opinion and what is tested and proven fact over the 'full' range of possible answers.

    Cheers, Slieve.

  • 11 Oct 2018 07:26
    Reply # 6717247 on 4793670

    I'm not sure if I can add anything of use, in truth, because I'm a junk sailor, not a designer. 

    Iron Bark is a 35ft Wylo with a long keel.  She also had a rounded bilge which might have been the reason she was tender.  But she also had some pretty heavy weights about deck level which might also have had something to do with it.  She wasn't particularly hard-mouthed; nor was she particularly balanced.  Nor fast, but she was well overweight.

    Passepatu wasn't set up properly and we had a right mishmash of weather that never gave me much of an opportunity to work out just what might work and what didn't. I have always wished I had a chance to sail the boat with simple battens in her flat sails, which would have told me a lot.  She doesn't have a centre board.  The big mast in the eyes of the boat certainly produces plenty of windage.  But she hove to like a duck (if ducks heave to.)

    Bronwen appears to have been a complete success and Asmat seems very happy with her.  I should certainly pick his brains before committing myself to any design.

  • 10 Oct 2018 17:35
    Reply # 6716212 on 6715627
    Christopher wrote:

    I very much like Roger Taylor's "hinged" sail, although I seem to have lost the article from one of the yachtie magazines about it, which I kept.  Is Roger a member?

    I'd love to hear from Annie if she has experience of sailing a junk Wylo - Nick tells me that there have only been a couple built so there's not a huge amount of experience to harvest.

    Yes, Roger is a member

    Have you looked at JRA Magazine 65, with Annie's account of delivering Passepatu, and JRA Magazine 70, with Asmat's account of converting Branwen - both Wylos?
    Last modified: 10 Oct 2018 17:38 | Anonymous member
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