Sail Balance - Position Relative to Mast

  • 23 Jun 2017 08:02
    Reply # 4913807 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.”

    David, you really do yourself no credit in writing such emotional nonsense. It must be clear to everyone by now that you are determined to rubbish the split rig, from even before you had your single experience of it.

    We sailed the rig that you had your one experience on in a boisterous Round the Island Race and achieved a creditable result despite not sailing it well, and at no stage was there any feeling of insecurity. We would have been fools to have done so if we had felt “at risk of being blown down, filling and sinking”.

    All I am saying is that is unsafe to go for the absolute maximum balance, with the risk of overbalance. That's all there is to discuss here - what figure to put on the amount of balance.“

    It is not unsafe to use a balance that has been systematically tested and proven to be safe and without risk of overbalance. It is butterfly engineering for you to pluck a figure out of the air and suggest using it as a maximum when tested results are available. That is the amateur approach to an engineering problem which if generally used would still have us struggling to achieve powered flight. If you think Edward is being defensive he is only reacting to your continual uninformed criticism which I also find extremely tiresome.

    It is clear that Bert's rig has not been built to the information I tried to make available, and the question has got to be what has gone wrong. It could be my writing and/or Bert's translation/interpretation, but certainly his resultant understanding and build is not what was intended. Unfortunately I have not had a chance to chat to him, but from the two photos that I have seen there clearly are problems. The first photo showed that the initial balance was not as intended, and the later one seems to suggest that the camber is also not as intended. We need more photos, and maybe even the drawing of the panel patterns to make a more informed assessment, but it appears that the jibs have a hooked or tight leech which is back-winding the main panels badly. Tight jib leeches will also have an effect on the rig's ability to freely feather into the wind, and will effect the overall stability. I suspect a fully flat sail would balance at around 25%, similar to a true symmetrical hard foil. We need to follow a systematic analysis of the problem and not make butterfly adjustments.

    The comments in one paragraph about the rig feathering and in the next saying it won't feather is confusion, and broaching through 180° is also not very clear. What is the total sail area, and what is the the oiginal designed junk rig area? Was the designed rig a flat Hasler/ McLeod rig? Is the boat being overpowered with a potentially more powerful rig? There is at lest one case of a boat becoming unmanageable when simple camber was introduced, and with hindsight was probably due to the professional sailmaker getting the shape of the camber wrong.

    Another question could be, is your mast vertical or leaning back a little with the boat in sailing trim and your weight in the cockpit? If the latter then gravity might tend to 'sheet' the sail in in light airs, which will fill the cambered sails and drive the boat. It is difficult to make an informed assessment until we know more about the build and set up, and pointless to simply speculate.

    Cheers,  Slieve.

    Last modified: 23 Jun 2017 11:03 | Anonymous member
  • 22 Jun 2017 09:17
    Reply # 4912252 on 4793670

    Hi Bert,  

    If I understand it correctly, what is happening, is that when you release the mainsheet, the sail comes around to a certain angle to the wind and instead of continuing until it is "head to wind", "luffed" or "feathered" and depowered, it stops at a certain angle to the wind, still powered up, and regardless of what direction you steer the boat, the sail maintains its angle to the wind, as indicated by your masthead windvane, and doesn't feather completely.  

    Is this still happening despite the changes to the jiblets?  

    Looking at photo no. 3 in your album, I see the main panel is back-winded while the jiblets still seem very full and powered up.  Is this back-winding present only when you released the sheet to depower the sail, or is it present all time even with the sail sheeted in?  

    The back-winding of the main is going to remove power ( and a turning force) from the main due to the loss of the force-producing camber.  

    If the back-winding is present all the time, then maybe the sheeting angle of the jib is not large enough to allow the jibs windward airflow, to pass safely to leeward of the main without back-winding it and/or the slot still isn't large enough.   

    If the back-winding of the main is only present when you release the mainsheet, but the jib panel is still full and powered up, I think that might indicate that;

      The jib camber is still too great and, as suggested by Arne, is helping to prevent the sail from feathering fully.  I imagine that the jib panel being luffed by the wind before the main would be what we are looking for here, so the full main is pulling the sail around the mast while the depowered jib has lost its counteracting force.  

      

    Apologies if you have already thought of the above.  

    Regards, Dave D



    Last modified: 23 Jun 2017 08:41 | Anonymous member
  • 21 Jun 2017 18:00
    Reply # 4911205 on 4910436
    Arne Kverneland wrote:...

    It appears that the sail of his Runa, has a labile balance. I can only speculate why it is so, but here is my armchair idea:


    Could it be that the jiblets are cut so they effectively are ‘sheeted in’ closer than the main panels? My thinking is that, as the alpha is reduced, the main panels are losing drive before the jiblets do. That could destabilise the rig. The obvious solution is that Bert makes a new set of jiblets, which he cuts to have a ‘slacker sheeting’ than the ones he has now. In my head, from a stability point of view, it is it better that the jiblets luff a second before the main section, than the other way around.

    Does that makes sense?

    Arne


    Hi, I have uploaded a photo of my sailing in calm weather with the new jiblets cut to 29% balance with main including slot.

    You can see that they have a broadseem in the middle  which is unconvenient, but as the old jiblets were cut down from 110cm to 80 cm at the leach the camber had to be adjusted by those broadseems.

    The jiblets have a sheeting angle of 8° degrees.

    The small red rectangle at the top of the picture indicates the winddirection, sail seems to be sheeted in a little bit  too much (but as I said: the sail searches this position by itself, sheets are totally eased, 1-2bft). The main shows a belly to weather which indicates that too.

    Sail is not set as it should (gap should be nearer to the mast). The battens still have their old length, will be cut to save weight and to avoid hazzle of lines wooling round them.


    Now to the fact of depowering the sail:

    I will try to loosen the downhaul, and I will loosen the sailcatcher (lazy). Sail should move then more freely.

    As my mistake shows, there is clearly a limitation of sailbalance, mine was 37%, which was without doubt too much.

    Bert





    Last modified: 21 Jun 2017 20:50 | Anonymous member
  • 21 Jun 2017 16:47
    Reply # 4911090 on 4793670

    the problem is not only related to the percentage of the balance.

    as all junk sails run half a mast diameter apart from the center of rotation, the feathering ability (and speed) may be different between both sides:

    • faster (and safer) with the sail on the windward side of the mast
    • slower with the sail on the leeside

    …this is 'armchair' stuff – based on geometric thinking, not on junk rig experience!

    ueli

  • 21 Jun 2017 16:25
    Reply # 4911039 on 4910954
    Deleted user
    robert self wrote:

    I think one thing can be said for sure: a 33% balanced rig will, on average, have a (slightly) longer response time than a 10% balanced rig 'cause the sail's turning moment is a function of wind force and turning arm (equals distance betwn axis of rotation (the mast) and horizontal cntr of area of sail). Geometry dictates a 33% balanced rig has a smaller turning arm. Sometimes that's a positive and others a negative. One man's response time is just too slow for comfort, perhaps?

    But the same can be said of a high-aspect-ratio sail versus a low-aspect-ratio sail. Everything else being equal, the turning arm of the high-aspect-ratio rig is less than the turning arm of the low-aspect-ratio rig.

    All you can really do is pick your compromises and adapt.

    robert self



    I'm confused on your physics here.  A longer turning arm also means a much longer trek to get around the compass points.  What keeps a sail from instantaneously assuming the new position is inertia. And our rigs tend to have more mass further from the axis than a Bermudian, due to the squareness of it all.   In order to turn faster, what with the conservation of momentum thing, a smaller radius is usually best, no? 

    Last modified: 21 Jun 2017 17:51 | Deleted user
  • 21 Jun 2017 15:04
    Reply # 4910954 on 4793670
    Deleted user

    I think one thing can be said for sure: a 33% balanced rig will, on average, have a (slightly) longer response time than a 10% balanced rig 'cause the sail's turning moment is a function of wind force and turning arm (equals distance betwn axis of rotation (the mast) and horizontal cntr of area of sail). Geometry dictates a 33% balanced rig has a smaller turning arm. Sometimes that's a positive and others a negative. One man's response time is just too slow for comfort, perhaps?

    But the same can be said of a high-aspect-ratio sail versus a low-aspect-ratio sail. Everything else being equal, the turning arm of the high-aspect-ratio rig is less than the turning arm of the low-aspect-ratio rig.

    All you can really do is pick your compromises and adapt.

    robert self


    Last modified: 21 Jun 2017 15:14 | Deleted user
  • 21 Jun 2017 11:46
    Reply # 4910660 on 4793670

    Hello Bert,  

    I've been following this thread with interest as I am still in the process of getting a split junk dinghy onto the water.  Other things keep getting in the way and I have a bermudan rigged dinghy to sail so less pressure to get it on the water.  

    I too took the 33% balance as "Sail Area" and not total profile forward of the mast and will either have to build a new jib or cheat for the moment and shorten the leech by an appropriate amount increasing camber but decreasing actual sail area until I do build a new jib.  


    Bert, I think that both Arne and Alain Herter may have both identified part of your problem.  I took another look at the photo of the rig in your album.  

    I'm wondering what are the camber percentages for the jib and main?  In the photo they both look almost flat to me.  And what is your sheeting angle for the jib panel? and the panels do look to be very stretched and flat on the photo.  

    In the photo, the jib sheeting angle looks to be non or almost non-existent.  This would have the same effect as a "backed" jib on a conventional Bermudan rig and be more inclined to pull the bow of the boat to lee.  On my bermudan dinghy, I measured the sheeting angle of the jib to the centreline as approx 23 degrees to leeward.  Forgot to measure the midsail jib camber unfortunately.  It wasn't very much though. 

    So Arne may be right,  not enough sheeting angle may be pulling the jib to leeward and not allowing the whole sail to feather fully into the wind.  Or it may be that you still have too much camber too far forward on the battens as well, generating too much lift, though it doesn't look that way from the photo.  


    Also in your photo, Alain Herter mentions that you may simply have too much tension on the downhauls and again, looking at the photo,  the panels do look very stretched which may make them less inclined to rotate around the mast. 

    With that sort of tension, is it easy to push the sail around the mast with the tips of your fingers.  Easing the tensions of the batten parrels/downhauls could be part of the solution to the non-feathering of the sail.  

    With regards to the "Scary" comment,  I'm with David on this one.  A boat whose sail won't feather is not confidence inspiring, though Edward and Slieve have since sorted out what seems to have been a teething problem on Edward's rig at that point in time.    

    Hope you come up with a solution, Dave

    Last modified: 21 Jun 2017 11:51 | Anonymous member
  • 21 Jun 2017 09:38
    Reply # 4910477 on 4793670

    Edward, 

    I do wish that you could stop being so defensive, and read my comments accurately. I am not saying that the split rig does not have its place in the overall scheme of things. It does. I am not saying that it cannot be configured as a cruising rig, rather than your inshore racing rig. It can. I am not piqued because I didn't think of it first. I might well have adopted it for Weaverbird, if the accommodation had permitted, because I have a long record of only speaking whereof I know, and would have liked to extend the range of my knowledge. I do have personal knowledge of overbalanced junk rigs, and they are unpleasant, at best, dangerous, at worst.

    All I am saying is that is unsafe to go for the absolute maximum balance, with the risk of overbalance. That's all there is to discuss here - what figure to put on the amount of balance. Bert has accurately described an overbalance situation. Whether he and his boat can tolerate that is for Bert to decide, and I guess he probably can.

  • 21 Jun 2017 08:46
    Reply # 4910436 on 4793670
    Anonymous member (Administrator)

    Hi Edward

    I don’t doubt for a second that your present rig behaves well, as you describe. On the other hand, Bert seems to be a resourceful chap who understands his boat quite well, so I don’t doubt on his report either.

    It appears that the sail of his Runa, has a labile balance. I can only speculate why it is so, but here is my armchair idea:


    Could it be that the jiblets are cut so they effectively are ‘sheeted in’ closer than the main panels? My thinking is that, as the alpha is reduced, the main panels are losing drive before the jiblets do. That could destabilise the rig. The obvious solution is that Bert makes a new set of jiblets, which he cuts to have a ‘slacker sheeting’ than the ones he has now. In my head, from a stability point of view, it is it better that the jiblets luff a second before the main section, than the other way around.

    Does that makes sense?

    Arne


  • 21 Jun 2017 07:28
    Reply # 4910370 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.

    David. I really wish you would stop rubbishing a rig that you know so little about. It makes you seem 'piqued' that it's one rig that you did not think of, or play with before anyone else. 

    I am still using the over heavy sheet i started with, because it is comfortable to hold. I use thimbles, not blocks, because i had them. So there is quite a lot of friction that could still be removed if it was necessary. Still in several hundred hours if sailing, summer and winter, I have never experienced the condition you purport to describe. Even with the. old sail you had a short trip with, I could always spill wind by easing the sheets, and i could 'heave to' simply by easing them right off and the whole sail would feather beautifully and calmly  

    If you are ever back in the area, you are more than welcome to come and sail Amiina again and evaluate her properly. 

    By the way, the remark you did make at the time, and seemed valid, that you would need to see how the jibs survived an ocean crossing before you would consider the rig, this would seem to have been more than adequately proved by Pete Hill's voyages in Oryx

    Come and have another sail in Amiina, and get over your prejudice. 

       " ...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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