Flat, hinged or cambered?

  • 13 Jul 2021 20:02
    Reply # 10749143 on 461931

    Hello

    Maybe these pictures of the junk Amoy help.

    Alex

    2 files
  • 11 Jul 2021 17:05
    Reply # 10744224 on 10742669
    Anonymous wrote:
    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.


    I hope I'm not being an annoyance, but looking at this again, I may have been fooled by a trick of perspective. If the mainsail is aligned fore-and-aft (can't be certain of this), then the battens could well be horizontal, just pointing to a vanishing point way off on the right horizon. Also, in that case, the balance wouldn't be as severe as I'd first thought, either.

    Curtis

  • 11 Jul 2021 00:58
    Reply # 10743098 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!)


    They appear to be using a bridal of some sort.... you can't always take how you see things rigged on a traditional Chinese junk as "the way" because they often had to work with limited resources and less than ideal materials. So the route and methods they took are not necessarily what we in the west would want to follow.

    It's always a case of look, learn and think..... just blindly following is not always going to get us the desired results. A lot of the ways and methods the Chinese (and other original users) used comes more from tradition than any real understanding of the basic principals. This is not to say they are wrong because obviously they mostly are not.

    What Arne, David, Slieve and myself are trying to do is to understand the why as well as the how to. Hassler and Vicent Reddish have of course pointed the way but even they did not get every piece of the picture. 

    We don't always all agree but from the (mostly minor) disagreements often emerges a clearer picture. Sometimes it just a mater of phasing.

  • 11 Jul 2021 00:42
    Reply # 10743081 on 10742843
    Anonymous wrote:

    Ha, Slieve, great minds etc.!

    I am thinking of making a half-size batten panel with B = 2.5m and do exactly such tests. I will make the test panel with my normal 8% camber and with the max camber point at 35% from the luff. Vertical balance indicator lines will be drawn onto the cloth at every 5% of B.

    I am mainly searching for the point of vanishing stability with the sheet slack, to see how far I can go without running into trouble.

    However, it would be easy enough to tuft the panel on both sides, and in particular fit telltales at the leech, to see what happens to the airflow when I sheet in the sail on this or that tack.

    Arne



    I suspect you will find it is somewhere around 30% of chord.


  • 11 Jul 2021 00:39
    Reply # 10743078 on 10741654
    Anonymous wrote:

    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.


    Ah ha, Thanks for a bit more detail, yes I can agree.


  • 10 Jul 2021 21:15
    Reply # 10742843 on 461931
    Anonymous member (Administrator)

    Ha, Slieve, great minds etc.!

    I am thinking of making a half-size batten panel with B = 2.5m and do exactly such tests. I will make the test panel with my normal 8% camber and with the max camber point at 35% from the luff. Vertical balance indicator lines will be drawn onto the cloth at every 5% of B.

    I am mainly searching for the point of vanishing stability with the sheet slack, to see how far I can go without running into trouble.

    However, it would be easy enough to tuft the panel on both sides, and in particular fit telltales at the leech, to see what happens to the airflow when I sheet in the sail on this or that tack.

    Arne


  • 10 Jul 2021 20:33
    Reply # 10742780 on 461931

    Arne, you posted a photo very many moons ago showing your first experimental cambered panel, made with a simple barrel cut panel. Would a one metre long model slung from a broom handle at various balance setting not give you a good starting answer?

    As the symmetrical NACA00 series foils have a balance point at ~25% it would indeed be interesting to see what the non-symmetrical soft cambered panel did, particularly as the presence of the mast would make the shape different on each tacks.

    Just a thought,

    Cheers, Slieve.


  • 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
    Anonymous member (Administrator)

    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 (Administrator)
  • 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

       " ...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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