Flat, hinged or cambered?

  • 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
    Anonymous member (Administrator)

    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
    Anonymous member (Administrator)

    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 (Administrator)
  • 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)
  • 09 Jul 2021 08:57
    Reply # 10739435 on 461931

    I'm sorry if you think I'm “ being deliberately obtuse in order to score a debating point” David, but you could not be further from the truth. I am simply asking for clarification of some of the statements you are making about rigs that are contrary to my understanding of the subject.

    For example, in you posting #10734664 you state, “You know full well that a lower yard angle results in more balance area, lower stresses in the sailcloth, particularly alternating stretching on the bias at the throat , and lower loads on any hauling parrels; all of which makes for a better rig for relaxed cruising”. Er? I don't believe this to be the case. 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. Also, I don't understand how the yard angle and balance effect the “stress in the sail cloth” as with properly set up cambered sails there should be no stress in the sailcloth, so how can it be lowered? When you add, “particularly alternating stretching on the bias at the throat” I'm totally lost as I don't know what this means. You continue with, “lower loads on any hauling parrels” which I agree can be achieved with lower yard angle and more balanced area, but only if you set the angle of the luff to balance the angle of the leech on tapered panels which is a key feature that you have not included in any of your drawings that I have seen.

    In the next two paragraphs you make comments on Arne's rigs, I can only say that Arne has followed a line of development based on the Hasler and McLeod rig and published most excellent information on how to get the best results form that particular rig. He must be congratulated on his continuous flow of helpful information. When he asked, “Could you elaborate a bit on where you have lowered the stress in the rigs with the profile (planform) you prefer, compared to the sails I design, - - ? Should Zebedee and Mingming II have their rigs remade?” it would have been useful to have seen your explanation rather than the dismissive remark about insulting his intelligence. It would appear that Arne is also struggling to understand some of the points you are making.

    I am not asking why Weaverbird'srig does not not have much balance, and do understand that letting the battens press on the mast may put less stress on the sailor than would come from luff hauling parrels, but do not believe that it puts less stress on the rig or less compression on the battens which is particularly undesirable with hinges.

    In the last paragraph you state,Weaverbird' - - might well have been wearing a SJR, - - Made according to my own ways of doing things, of course, and having cast a seaman's eye (?) over - - Amiina, and noted some areas where I believe that there is room for improvement.” If you are trying to improve the breed then help by explaining the “areas where you believe that there is room for improvement.” I am happy to change my notes when I learn of possible improvements (as I did a few hours ago when out of the blue I received a call from someone who has been sailing a SJR for about 10 years, to tell me about experiments with combined batten/ downhauls on the yard and top batten).

    In my efforts to reduce the stresses when initially drawing the Poppy rig I tried to calculate the slope of the luffs to balance the slope of the leeches and did not find a satisfactory answer, so reverted to model making. As Arne quite rightly points out, the tensions from the main sheet complicate the issue and I do not believe I have found the best answer, but so far it has worked adequately. You claim that the calculations are easy so please explain how to do them so that others can use the technique.

    You seem to infer that yard angle, sail balance and rig stress are tied together. I do not look at it that way as 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.

    David, you must expect to be challenged if you make sweeping statements which contradict accepted experience or appear to be incomplete and omit critical points. I am not claiming to know all the answers which is why I am simply asking for clarification to some of your postings.

    Cheers, Slieve.


  • 09 Jul 2021 01:52
    Reply # 10738958 on 10738945
    Anonymous wrote:
    Anonymous wrote:
    Anonymous wrote:

    snip

    The correct angle is easily found by making a circle whose center is where the slingpoint should be and whose diameter is the width of the head of your sail. A chord that passes through the centre of the circle at any point will give you the required balance for that particular angle.

    snip

    Paul,

    Could you perhaps provide a simple graphic example of this procedure? My rusty old brain is failing to visualize it from the text.

    Thanks,

    Curtis

    Find below, hope it helps you.

    Thanks!
  • 09 Jul 2021 01:46
    Reply # 10738953 on 10736952
    Anonymous wrote:

    HK-parrels.
    I struggle with understanding the resistance against using these. They now surely live an easy life, after the THP came into use, but to me they still add that little, but useful support to keep each panel setting well. The support they give lets me tack into a head sea without need for a lower LHP or short batten parrels to support the luff. The HKP is anyway super easy to install, and can be made of just about any ol’ piece of string.

    Okay, I'll take another look at them this summer....

    These days I am more focused on keeping the sail as trouble-free as possible in use, and to see to that the sheets and thus twist is correct (=low). I ensure that the leech is vertical or even lists a bit aft, and I try to tie the battens flush with the leech, both to avoid sheet-batten tangle. The remaining challenge is to make the foresail sheets of a schooner work properly, i.e. without snagging the mainsail, and still keeping the twist right..

    Fully agree with the above, I've been playing a lot with sheeting on LCB and I expect to have something to discuss by the summer. I've been finding double sheets to be a right royal pain, except for the Mizzen where they work very well. I've managed to make the main single sheeted and am now working on the foresail which is a much tougher nut to crack. However I think it is just doable.

    Inputs are welcome.

    Cheers,
    Arne


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