Sail Balance - Position Relative to Mast

  • 20 Jun 2017 19:01
    Reply # 4909612 on 4793670

    "I cannot totally depower the sail. If it is up, it is all under tension due to the battens"

    Do you mean the weight of the battens ?

    Just armchairing around (sorry): What is the tension in your batten-downhauls ?

    If tensioned, I would imagine that the batten downhauls  could inhibit the sails fathering, especially in a small sail, as they are fixed at one point near tne mast.

  • 20 Jun 2017 15:25
    Reply # 4909366 on 4908942
    Scott Dufour wrote:

    Hi Bert,

    Can you help me understand these two statements better?  You mention that the rig feathers into the wind if the sheets are let go, but then state that the sail doesn't rotate into the wind.

    Does the second paragraph mean that you are unable to stall the boat and bring it to a completely unpowered state?  Or is it that it is more forgiving of an imperfect angle of attack, and the sail generates power over a wider range of wind/boom angles than you're used to as a Bermudian sailor.  The first situation is scary, the later really cool for lazy helmsmen like me.

    Hi Scott,

    I cannot totally depower the sail. If it is up, it is all under tension due to the battens. A bermudian sail with sheets eased will flap. As soon as the (should I say "my"?) splitrigsail fills with wind you go ahead, the sheets can be eased, but the sail will still search an angle of attack (perhaps friction in the sheeting as Robert mentioned is an issue). Maybe it can be depowered for some five seconds, but as soon the wind fills the sail you go or you have to steer active to weather (I did not try heaving to). The only way of stopping is pulling the sail down, as you say: "the sail generates more power over a wider range of boom/wind angle". Maybe you will not encounter this phenomen on a bigger boat because of its mass.

    @ David: Farthing is a very safe boat. To make her sink, you have to turn her to 130 degree (with her hatch open), which means 440kg of keel weight in the air and you have to put the mast (wood) under water. A big breaking wave could do this.

    Bert

    P.S. Please be aware that it is not the original farthing, it is 10% scaled, so displacement and weight is higher.
    Last modified: 20 Jun 2017 16:25 | Anonymous member
  • 20 Jun 2017 14:15
    Reply # 4908997 on 4793670

    I'm reading this in the "scary" sense, as it's precisely what I experienced in Amiina. A light, over canvassed boat is at risk of being blown down, filling and sinking, though I guess Bert's boat should be safe enough.

  • 20 Jun 2017 13:19
    Reply # 4908942 on 4905795
    Bert Qui wrote:

    ... No leehelm anymore, the rig feathers to the wind, if the sheets are let go. I can sail to any direction I want to. Yeah, success :-)

    ...

    The problem is, if you want to let the sheets go, the sail really doesn't want to go in to the wind - the sail still produces lift even if the sheets are loose.

    I observed this phenomen while sailing in normal conditions: Sheets are loose, the sail acts a little bit like a kite or a wing - it sails by itself, there are nearly no loads on the sheets. That is quite a nice feature, sail position is on halfwind and you just steer the boat into another direction, say more close to the wind and you just point higher, without pulling the sail in. On the other hand this is quite an unusual feature for a "normal" sailor...


    Hi Bert,

    Can you help me understand these two statements better?  You mention that the rig feathers into the wind if the sheets are let go, but then state that the sail doesn't rotate into the wind.

    Does the second paragraph mean that you are unable to stall the boat and bring it to a completely unpowered state?  Or is it that it is more forgiving of an imperfect angle of attack, and the sail generates power over a wider range of wind/boom angles than you're used to as a Bermudian sailor.  The first situation is scary, the later really cool for lazy helmsmen like me.

    Last modified: 20 Jun 2017 13:19 | Anonymous member
  • 18 Jun 2017 20:26
    Reply # 4906320 on 4793670

    Thanks for your response, Annie. The boats can be compared, yes, but the coin collection hulls are quite more slender than the Herreshoff fish or buzzard bay, so they heel very quick. Runa has 440 kg lead, depth is 88 cm.

    I looked at the wind reports for the past sailing days and could see the gust which has blown us down.

    Bert

    Last modified: 18 Jun 2017 20:27 | Anonymous member
  • 18 Jun 2017 09:41
    Reply # 4905884 on 4793670
    Bert, this information may help you.

    The recently launched Francis, is a dainty, 5 metre boat, built of wood to Herreshoff's Buzzards Bay design, slightly lengthened from the original 14ft and fitted with a wee cabin.  She was recently launched with a rig that is part way between a Split Junk Rig and an Aero-junk.  (As, until Oryx left a few days aog, there were three of these in NZ waters, perhaps it should be known as a Kiwi-junk!)

    This is what she looks like:

    and you can see the larger photo here.

    Some salient details of the rig that may be of interest to you, as being comparable with what you are doing:

    The boat:

    LOA 5.63m/18’ 6” (including the rudder)

    LWL 4.69m/15’ 5” 

    Beam1.90m/6’ 3” 

    Draught 0.76m/2’ 6” 

    Displacment 770kg/1700lbs

    Ballast 363kg/800lbs

    The rig was designed with 7% lead (taking the rudder into account) and a sail area of 16.72 sq m, with the jiblet being 26% of the total sail area.

    The mast is of hybrid construction, with an alloy lower part and a douglas fir topmast.  The length of the mast is 7.5m overall, 6.5m above partners. The lower mast is a 125mm diameter, 5m aluminium tube (6063 T6), with a 3mm wall thickness.  The topmast is 2.5m long and solid.

    Mast weight 25kg; battens and yard10kg; sails 8kg.

    Although Francis has only been out a few times under her new rig, she is apparently a delight to sail, perfectly balanced, close-winded and very fast.  Having seen her sailing, I would be prepared to endorse that report.

    I hope this is of some help to you.

    (Please excuse the weird mix of fonts.  I've copied and pasted some of this and my efforts to tidy it up didn't work.  It's late and it's time I had something to eat, so I'm afraid it will have to stand.)



  • 18 Jun 2017 08:09
    Reply # 4905795 on 4793670

    As promised I want to keep you updated about Runa`s splitrig. The jibs have been changed to 80cm batten length, the main has 220cm, the slot is variable because I did not sew the jibs to the toppanel but remained at about 15 cm (mast has 10cm).

    Now the facts of my sailing last week: No leehelm anymore, the rig feathers to the wind, if the sheets are let go. I can sail to any direction I want to. Yeah, success :-)

    The wind has been very moderate (2bft), but on one sailing there have been gusts up to 4-5bft (out of nowhere) - I must say: with four panels up (incl. top =5, means I had one panel reefed) I managed to put her on her ear and broached, Runa made a turn of 180° in a circle of 7-8m. Scary! At this moment I looked at the mast, hoping, nothing would break - but everything was ok.

    The problem is, if you want to let the sheets go, the sail really doesn't want to go in to the wind - the sail still produces lift even if the sheets are loose.

    I observed this phenomen while sailing in normal conditions: Sheets are loose, the sail acts a little bit like a kite or a wing - it sails by itself, there are nearly no loads on the sheets. That is quite a nice feature, sail position is on halfwind and you just steer the boat into another direction, say more close to the wind and you just point higher, without pulling the sail in. On the other hand this is quite an unusual feature for a "normal" sailor...

    The sail seems to act as an airplane wing?

    Next question:

    On a small boat like Runa (5m length) the rig is quite heavy, but I must say, I did not cut the battens down yet because maybe I would have had to change the sailgeometry once again. I can save now about 1.5 kg when cut to the right size, the complete rig weighs at the the moment 13 kg, the battens are aluminium 38x1.5 mm (each batten has a weight of 1,65 kg). Dear technician experts - is there any chance to cut down the weight by using any other batten diametres or any other material than alioy aw-6060, t66? The yard is a part of an old windsurf mast, made from polyester and is yet very light.

    Bert




  • 17 Jun 2017 10:18
    Reply # 4904876 on 4793670

    So when creating such a rig for Coromandel Siskin with it relatively far aft mast position, I think you would agree I should stick to 20 - 25%?

    If you want to use guesswork and get less than the maximum benefit from a split rig then the answer is yes. On the other hand, if you are prepared to use the wisdom gained from a set of controlled experiments then the answer is that you can safely place 33% area in front of the mast as long as you don't extend the moment arm. If you include the slot in the area in front of the mast then there will be no problem. I have sailed on a split where I am led to understand that the balance was set at 36% of the parallel batten length and found the rig to be stable.

    If you use the 33% balance then your most likely problem will be too much power from the rig. Area for area the split rig produces more drive than any other junk rig I have sailed on. Where PJR advocates using more area than the full fore and aft Bermudan rig when converting to junk, with a split rig it is not necessary. Poppy had less than full Main + No.1 Genoa and never seemed under canvassed.

    I have heard of split rigs that haven't shown much gain in performance, but when checked have found that they have not taken full advantage of the rig's possibilities. If you want the performance of a split rig then use the already proven information. Those who have have not regretted it.

    Cheers, Slieve.

  • 10 Jun 2017 15:53
    Reply # 4891012 on 4793670
    So when creating such a rig for Coromandel Siskin with it relatively far aft mast position, I think you would agree I should stick to 20 - 25%?
  • 26 May 2017 11:17
    Reply # 4853975 on 4793670

    I think, Edward, that we are seeing that day's sail from two different perspectives. 

    I, parachuted in, saw a rig that had not yet been fully sorted, and took away a "snapshot" of that. There was certainly one squall, as we sailed to windward towards our temporary anchorage, when I was unable to spill wind as the sheet went slack while the sail remained full. I may not have given full voice to my concern, but I could see how the boat could have been blown down in a stronger squall. At the same time, I remember remarking upon how close-winded she was, when sailing well.

    You, on the other hand, have a memory of that day as just one among many, as you developed and improved the rig. After having made some necessary adjustments, the rig became safer, of that I have no doubt.

    My point was, and is, that it's not sensible to push this "more balance is better" way of thinking as far as it will possibly go.

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

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