Flat, hinged or cambered?

  • 10 Jul 2021 19:42
    Reply # 10742669 on 10741903
    Anonymous wrote:

    A limit?

    Amoy in 1922 after passage from Shanghai to British Columbia, Capt. George Waard.

    There’s low yard angle and high balance for you.

    Looks like at least 25% balance.

    There is a mizzen which is obscured.

    Note the witness marks of an upper batten, on main and fore sails, which have evidently been removed.

    A blow up shows an array of running parrels.

    Where do you reckon the halyard sling points are here?


    I imagine the Chinese probably found the limits centuries ago.

    (They never thought of splitting it though!)



    It looks to me like the mainsail is hanging wrong. Aren't the battens supposed to be more or less horizontal instead of sagging backwards? The more I look at it the more certain I am that this photo was taken while the crew was in the middle of reefing.

    Strange arrangement with the main yard, too, and as it is in the picture, it looks more like 33% balance than 25%. I bet the balance of both of those will be a lot less once it's set for sailing.

    Take these comments with a tablespoon of salt, of course; a year ago I scarcely knew a halyard from a sheet. Love the sweeping curves of that hull, though. I could look at that all day.

  • 10 Jul 2021 11:18
    Reply # 10741903 on 461931

    A limit?

    Amoy in 1922 after passage from Shanghai to British Columbia, Capt. George Waard.

    There’s low yard angle and high balance for you.

    Looks like at least 25% balance.

    There is a mizzen which is obscured.

    Note the witness marks of an upper batten, on main and fore sails, which have evidently been removed.

    A blow up shows an array of running parrels.

    Where do you reckon the halyard sling points are here?


    I imagine the Chinese probably found the limits centuries ago.

    (They never thought of splitting it though!)


    Last modified: 10 Jul 2021 11:22 | Anonymous member
  • 10 Jul 2021 10:45
    Reply # 10741838 on 461931
    Anonymous member (Administrator)

    The upper limit for mast balance on an un-split cambered junk sail

    One thing remains to be found out; how far can we go?
    What is the maximum balance an un-split junk sail can have before it gets unstable  -  25%, 30? I never thought about this in the early days of the cambered JR, since I was so afraid of distorting the camber on one tack. Now that the use of 22% balance has proved to work well on both tacks, with the telltales flying nicely from the leech, I think it is time to find the upper limit.

    By finding this, and then rig the sail so that it is just on the safe side, one can make very large rigs, say 60 or 80sqm and still have sheets and running parrels which are manageable for normal, mortal people.

    This sort of sail could also be useful on the foremast of a schooner.

    Any suggestions?

    Arne

  • 10 Jul 2021 08:18
    Reply # 10741654 on 461931

    Hi Paul,

    I find your latest posts most interesting, but I don't think we actually disagree on yard angle/ balance and rig stress. Where I said, “A lower yard angle does not have to have more balance as it is possible to have a lower yard angle and low balance if appropriate parrels are fitted” I did not say that the loads on the 'appropriate parrels would be 'low stress'. The more extreme the shape the higher they would become, and in my eyes is not a practical way to build a rig, but it is possible.

    Later I said, “I select the yard angle which I feel will give the lowest tip vortex/ induced drag, the balance that will give the most useful camber in the forward part of the rig and a low sheeting load, and only then draw the rig profile to minimise the stresses in the rig. I see them as three separate issues.” The interesting thing is that that has resulted in a rig shape the falls in with your recent posts, and if properly done can result in a rig with no hauling parrels.

    A number of SJR sailors have told me that by making a quite small fore or aft adjustment to the sling point and tuning the downhaul/ batten parrel attachment points they have eliminated the need for any running adjustments completely. All this and no structural stress in the sail cloth seems fairly ideal to me. Adjusting the attachment point of the standing part of the halyard does adjust the final halyard force along the yard, so I think I can safely say that we do agree.

    Anyway, I hope we do.

    Cheers, Slieve.


  • 10 Jul 2021 01:21
    Reply # 10741242 on 10739466
    Anonymous wrote:
    Paul wrote:Find below, hope it helps you.


    Very elegant, Paul.
    All I need to do then is to copy that diagram, but with the slingpoint moved to the  55% position. That is what I use these days, to reduce the loads on the YHP.

    Arne


    I prefer to attach the block at 50% and just lead the standing part of the halyard aft. However that only works for an uneven purchase. ie. 3, 5, or 7 part halyards.
    1 file
  • 10 Jul 2021 01:15
    Reply # 10741236 on 10739727
    Anonymous wrote:

    Paul's diagram

    Sorry Paul, but that doesn't do it for me.

    Elegant, yes - but the notion that sail balance follows yard angle seems to be  based on circular reasoning (no pun intended). I was going to ask the same question as Curtis, because I too could not understand what you meant. Now I see the diagram, I can understand what you are saying but I still don't follow your reasoning. That thing only works because evidently hauling lines force the slingpoint to stay fixed in that position. But wait a minute - hauling lines can make the sling point take any position you like (within reason). As Slieve stated (in relation to a different argument) "


    Yes Graeme, you can force the slingpoint to any position that you may wish too but if you want a low stress rig that falls into place with the minimum of hauling and shoving and that is easy to set up, the the relationship I laid out holds true. Needless to say, I don't agree with Slieve on this point. I've made quite a few sails to date and I've found that the relationship holds true in every case..

    BTW: When you position the sail the way I show it, the head of the sail falls as shown without needing any lines to pull it there. The foot of course does need to be pulled back a bit as do the other battens but the force required is minimal.

    Last modified: 10 Jul 2021 08:12 | Anonymous member
  • 10 Jul 2021 01:12
    Reply # 10741228 on 461931

    Thank you Arne, I am now starting to get some idea - there are a lot of factors at play which are not all mentioned, but all need to be harmonised. So I leave the mysterious world of sail design to you guys, and rejoice that you are sharing your ideas and making continual progress.

  • 09 Jul 2021 20:19
    Reply # 10740730 on 461931
    Anonymous member (Administrator)

    Here is another way of doing it:

    Four yard angles, four different values of mast balance.

    Check the diagram below. I have basically used variations of this to find the right yard angle in response to needed mast balance.

    To make it work, I set up a few rules first:

    • ·         The sail is a Hasler-McLeod style sail with yard, battens and boom of the same length, and with parallel lower battens.
    • ·         I choose to have a boom rise of 10° (and lower-batten rise the same).
    • ·         I choose to set the sail with the luff parallel with the (plumb) mast.
    • ·         I attach the halyard 5% aft of the middle on the yard.
    • ·         I choose to have a net halyard drift of 0.18B. This has proved to give ample room for the yard and halyard blocks.
    • ·         The default halyard angle is here 15° aft of the mast. This gives us freedom to vary that angle with +/- 7°, which will increase or decrease the mast balance with a bit over 2%. In other words, the four yard angles are enough to have overlapping amount of mast balance.

    One can exceed these rules by making the halyard drift longer (taller mast) and by shifting the slingpoint a little back and forth

    Others may want to make their sails with different boom rise, mast rake or have a shorter yard etc. so should play with sketches until a finished sailplan can be made.

    Arne


    Last modified: 10 Jul 2021 09:22 | Anonymous member (Administrator)
  • 09 Jul 2021 12:37
    Reply # 10739727 on 461931

    Paul's diagram

    Sorry Paul, but that doesn't do it for me.

    Elegant, yes - but the notion that sail balance follows yard angle seems to be  based on circular reasoning (no pun intended). I was going to ask the same question as Curtis, because I too could not understand what you meant. Now I see the diagram, I can understand what you are saying but I still don't follow your reasoning. That thing only works because evidently hauling lines force the slingpoint to stay fixed in that position. But wait a minute - hauling lines can make the sling point take any position you like (within reason). As Slieve stated (in relation to a different argument) "A lower yard angle does not have to have more balance as it is possible to have a lower yard angle and low balance if appropriate parrels are fitted."

    I am not trying to be contentious, and more than willing to believe that your diagram is, in some arcane way, a useful aid in the design of a contiguous junk  sail - you and Arne know much more about that than I do - but I fail to understand how the diagram demonstrates that "the balance of a sail changes with yard angle" - that seems only to be so because you make it so, by using the appropriate running parrels.

    Actually, it is evident to me that the lower yard-angle sails DO usually seem to be associated with higher balance, so I am not arguing. I simply don't understand why.


    Edit: After further thought, I am guessing an answer here.

    "In order to keep the force required on the hauling lines, and the stress on battens, to within reasonable limits, it is desirable to give more balance to a sail which has lower yard angle - and for a higher balance sail, to give it less yard angle..."

    Would that be right?

    Actually, it is slowly starting to dawn on me that if you have a high yard angle, then you MUST reduce the balance, otherwise the sling point gets too close to the mast and might even get in front of it, which I suppose would be absurd. I suppose I am now  about half way towards understanding. I still don't understand why a low yard angle sail can not be given low balance...

    Last modified: 09 Jul 2021 13:25 | Anonymous member
  • 09 Jul 2021 09:16
    Reply # 10739466 on 10738945
    Anonymous member (Administrator)
    Paul wrote:Find below, hope it helps you.


    Very elegant, Paul.
    All I need to do then is to copy that diagram, but with the slingpoint moved to the  55% position. That is what I use these days, to reduce the loads on the YHP.

    Arne

    Last modified: 09 Jul 2021 10:32 | Anonymous member (Administrator)
       " ...there is nothing - absolutely nothing - half so much worth doing as simply messing about in junk-rigged boats" 
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