Sail Balance - Position Relative to Mast

  • 19 May 2017 20:44
    Reply # 4842624 on 4793670
    Deleted user

    I've been sailing my split-junk for 2+ yr now in sheltered Puget Sound waters in F2-F6. My sail has 33% balance. You can see all the specs on boat and sail in my albums.

    I have had no issues with weather-cocking, gybing, tacking or even S-bending. For reasons related to the interior accomodation I placed the sail's COE aft of the Bermuda rig's COE. For comparison the B-rig geometric lead was 18% (taken from study plan scale drawing). The split-rig's geometric lead is 12%, Arne's informed 5%-LWL-correction-for-camber gives 16% lead. In practice no obvious difference in helming betwn B-rig and split junk....weather helm picks up around 15 deg of heel to windward and when pressed hard off the wind. Nothing to do with the rig....mostly caused by fore-aft volume imbalances in the hull. Put reef(s) in and helm forces ease.

    Bert, how about friction in the sheeting prevented weather-cocking in the low wind speeds you describe? My sheeting is the minimum 3:1 mechanical advantage which on the plus side means minimal friction when sheets are let go.

    Another related issue is sail area. D/L's for the coin series are 350-450. Very heavy displacement. Did you enhance or reduce sail area vs the design SA? At F1-F2 the force per unit area times sail area were insufficient to overcome friction?

    I'd also look to Macnaughton's coin series hull shape. The lines are Mcnaughton's versions of traditional wine glass as per Quay Punt, Vertue, Wanderer...but beamier (?) and since not many of the coin series designs were built and sailed the trial-and-error part linking theory and practice of a hull's design is missing. You're doing the trial and error now.

    In time you'll be able to instruct Mcnaughton on where the sail's COE actually should be located.

    robert self


    Last modified: 19 May 2017 21:07 | Deleted user
  • 19 May 2017 15:08
    Reply # 4841978 on 4793670
    Deleted user

    My first thought about the failure to weathercock is that in order for that sail to turn, it has to have some resistance to turn against.  It might be that with the heavy lee helm, the forces at work make it easier to turn the boat than the sail.

    In any case, that lee helm is frightening when it happens.  I once nearly T-boned a $2 million yacht with 17' foot cat ketch because the mainsheet (forward sail) stuck but the mizzen ran out as it should.  I actually snapped the tiller extension trying to bring her around.  A scratch on that yacht would have cost me more than my house.  I bought collision insurance the next day.

  • 19 May 2017 14:55
    Reply # 4841969 on 4841701
    Edward Hooper wrote:

    Hi all

    With 33% balance absolutely no problems with easing the sheets to spill wind, or with going about or gybeing. 

    When, I sailed on Amiina, there was very definitely a problem with easing the sheet to spill wind, but I think you have a different sail now, which may behave differently. Nonetheless, I still consider it dangerous and unseamanlike to push for as large a balance as 33%. Were I to design a split rig, I would be keeping it well under 30%, and nearer to 25%.
  • 19 May 2017 13:04
    Reply # 4841811 on 4793670

    Thank you, Annie. A picture of the boat with sail up is in my album.


    Edward, the mastposition had been changed to aft in order to have the sail center where it should be.

    Why my sail did not weathercock - I do not know. As you both, Edward and Slieve, had no problems with the balance of 33% I thought my sail would be right too.

    Maybe the combination with the leehelm led to this phenomen.

    Some interesting thoughts have been written here:

    http://www.junkrigassociation.org/general_forum/1348650?mlpg=2#1348650

    Last modified: 19 May 2017 13:22 | Anonymous member
  • 19 May 2017 11:51
    Reply # 4841701 on 4793670

    Hi all

    With a split-junk rig you do not want the mast in the same position as a normal junk. 

    In fact much closer to the Bermudan position. 

    We reckon with a Folkboat we could use the same position as the Bermudan version. 

    Amiina has her mast 6 inches only forward of the original Van der Stadt design. 

    With 33% balance absolutely no problems with easing the sheets to spill wind, or with going about or gybeing. 

    It is all about getting the CoE pof the plan in the same fore/aft position designed for your boat. 

    Good luck. It is certainly worth persevering. 

  • 18 May 2017 22:50
    Reply # 4840877 on 4793670

    You look to have built a beautiful boat there, Bert.  I'm sorry to hear you are having some issues with your rig.  Why don't you put your sail plan drawings in your albums so that the split junk aficionados can play around with them and see if they can work out what the issue is? 

  • 18 May 2017 20:19
    Reply # 4840472 on 4793670
    Would reducing the camber on fhe jib panel and/or increasing camber on the main help with the (non) weathercocking?
  • 18 May 2017 19:33
    Reply # 4840345 on 4793670

    Weathercocking: Yes, it seemed to me that the sail did not want to go into the wind. Weather was very calm (1-2bft).

    When the wind increased a little bit, the sail even came in close to the centerline of the boat.

    When the wind became a little bit stronger, the boat heeled due to the increased pressure, now more from the side, and rushed away. Normally one would steer now to windward but no way to get around, no reaction when letting the sheets go, the sail did not swing out. Only 2 possibilities left: jibing or taking the sail down. My first trial was on a river near the waterfront, jibing was not more possible, thanks to the junkrig the sail came down in less than a second and saved the boat.

    As I could not make any changes last year because the jibs and main were fixed together (sewn at the lower end of the toppanel), the only way to reduce leehelm was to move the whole unit back. Leehelm was a little bit reduced but still severe. When the wind got stronger tacking was still not possible. Maybe this would not be an issue on another boat (Farthing has a long keel and holds course well, secondary she was not fully loaded which means she has a very sensible trim = stem comes out of the water, stern sinks and so the CLR moves aft). I decided to have a good deal of weatherhelm to be safe, so I reduced the balance between jib and main. The lead between CE and CLR is now at 15% of the waterline, which seems to be ok for a longkeeled boat, if I am not wrong. For the next trial I did not join the "new" jibs and main, they will be fixed together when all is like I prefer.




  • 18 May 2017 16:48
    Reply # 4840083 on 4793670
    Deleted user

    Bert,

    Thank you for posting your experience with the split rig.  Your input here is very valuable to those of us working on the split rig ourselves.  It gives me pause as I design my own.

    It seems like you had difficulties with two types of balance: 

    1) balancing the sail center of effort vs the hull center of resistance (lee helm).

    2) balancing the sail area forward and aft of the mast (poor weathercocking of the sail itself).

    You mentioned that you used the same mast position and COE as the original flat cut sail.  That might explain the lee helm issues.  That split rig sure does move the COE forward.  I'm moving my mast forward from the original Bermudian, but not as far forward as many JR, for that reason.

    But the second one worries me a bit though.  If the sail is truly that resistant to pointing to the wind when the sheets are let go, it could cause all sorts of trouble.  Was is merely slow to come around, or worse?

  • 18 May 2017 16:07
    Reply # 4840027 on 4793670

    Hi all,

    that's my first posting here :-)

    I own a Farthing by MacNaughton and gave her a split junkrig. I followed the descriptions of Slieve but changed it to a rig like amina (1 toppanel). Balance was 33%, sail centre at the same position as the flat designed sail by the Designer.

    I encountered strong leehelm (very dangerous, because no tacking possible). It seems as if the cambered sail has its centre of effort more forward than the flat sail. I just finished cutting the jibs at the leek, balance is now 25%. Because the splitrig can't be moved forward or aft, it is all trial and error. Trial sail will be in june. Hope it will fit!

    By the way: My impression was that the sail wasn't willing to act as a weathervane as desired. The camber forward seems to balance the "main" sail.


    Best wishes to all!

    Bert

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

                                                              Site contents © the Junk Rig Association and/or individual authors

Powered by Wild Apricot Membership Software