Flat, hinged or cambered?

  • 09 Jul 2021 01:35
    Reply # 10738945 on 10738259
    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.
    1 file
  • 08 Jul 2021 20:03
    Reply # 10738259 on 10736378
    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

  • 08 Jul 2021 09:32
    Reply # 10736952 on 10736378
    Anonymous member (Administrator)
    Paul wrote:

    Arne, what I would call a low stress rig, is one that, as nearly as possible, takes up it's required position, before putting on additional lines. This means minimal loads on the lines required to pull it into position and to get the sail to set well.



    Thanks Paul,
    I think that is a good definition. It has taken me some time to get there. The point is, when I started with cambered-panel JR back in 1992-93, I was afraid that the drive would suffer with the mast to leeward. In addition, deck layout on Malena, and even more on Johanna favoured low mast balance. Therefore, the balance ended around 10-11%, which results in a higher ‘offset angle’ and thus higher load on the THP-YHP pair.

    However, when hearing about your La Chica, which went well on both tacks, even with 22% balance, I started to relax my low-balance attitude.
    When shifting Ingeborg’s sail forward to do away with some weather helm, I noticed a considerable drop in the THP-YHP forces. I had already moved the halyard’s slingpoint to the (ca) 55% point and the YHP about 2/3 up the yard, and this also helps: The longer the distance from YHP-point to the throat end, the lower forces are needed to get the same peak-up moment.

    It was then sheer luck that Ketil Greve came and asked for a new JR plan for his Kelt 8.50. Thanks to strict demands on mast position, the sail would need 22% balance. This sail now goes up without any need for a THP. And yes, she sails well on both tacks, and helm balance is fine. The running lines Ketil has to play with are the halyard, sheet and YHP (plus running lazyjacks), period.

    This was a good lesson. I may well end up making another string or two of master sails, one with 60° and one with 65° yards. Even when using the 70° yard, I will try to keep a mast balance of at least 15%.

    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.

    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..
    Inputs are welcome.

    Cheers,
    Arne

    Last modified: 08 Jul 2021 09:51 | Anonymous member (Administrator)
  • 08 Jul 2021 02:44
    Reply # 10736378 on 461931

    Arne, what I would call a low stress rig, is one that, as nearly as possible, takes up it's required position, before putting on additional lines. This means minimal loads on the lines required to pull it into position and to get the sail to set well.

    As you have said (and I've also said) one of the keys is the relationship between sail balance and yard angle. More balance, lower the yard needs to be. Less balance, higher the angle it needs to be. 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. I've also found that in practise, the slingpoint likes to be closer to the mast than applying Hassler's rules would give you.

    The other major thing that I've found that helps to keep stress low is to attach the standing part of a three or five part halyard roughly 5% of the yard length aft of the slingpoint. The effect is not as great for a five part halyard so for that I generally allow more drift. I've found that doing this alleviates the need for a THP.

    To date, I've not found that I need Hong Kong parrels. I normally just use two running parrels and sometimes a standing parrel connecting the second and third battens from the bottom. That plus a YHP is all I use. I also now use Dyneema for my batten parrels as it does not stretch. I put batten parrels on all the battens and the yard. The batten parrel on the yard helps to keep it under control when hoisting in a seaway and it also makes sure that the forward end of the batten can never slip around the mast.

    With due respect to David, I entirely fail to see any need for jointed battens today. Sewn in camber is always going to be more reliable than joints nor do I find that jointed battens can be relied upon to flip as intended. As for joints plus camber, to me that is putting every possible complication one can into a sail and I don't see the point. What I've seen with Annie's sail, just strengthens my belief that it's not the way to go.

  • 07 Jul 2021 18:11
    Reply # 10735306 on 461931
    Anonymous member (Administrator)

    Bringing in the Tystie Mk1 sloop rig...

    Now I took the trouble and traced and scaled down the Mk1 sloop rig of Tystie to 35sqm, and put it side by side Ingeborg’s aft-set sail. Now, that is what I call an extreme sail, with an offset angle of no less than 32°. I can understand that David had to struggle with the full-size version of that sail. The Ingeborg-sail looks quite balanced in comparison.

    However, this exercise has taught me to keep an eye on that offset angle, and aim for no more than 17° on sails over 50sqm. This is easier to achieve with hi-AR rigs than with the four rigs shown here.

    Arne


    Last modified: 08 Jul 2021 09:57 | Anonymous member (Administrator)
  • 07 Jul 2021 14:18
    Reply # 10734664 on 461931

    Slieve, I get that you're being deliberately obtuse in order to score a debating point.

    The question is why? 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.

    Arne knows it too, as he has just reported on how these desirable characteristics are evident in Ketil's new sail; and knowing Ketil's need for speed, I don't imagine that any tradeoff in terms of poorer performance would have been acceptable. 

    It really isn't more difficult to grasp than that. There is a possible range of yard angles, just as there is for batten angles and all other aspects of the geometry of the JR. I postulate that the range of yard angles that is easiest to live with is 45˚ - 60˚. Angles of 70˚ - 80˚ result in higher stresses, and having tried such angles, I am no longer prepared to accept those stresses. Lower angles carry with them the possibility of overbalance (except in the special case of SJR), which is unpleasant and potentially dangerous. There isn't any calculation to be made. There is simply the choice of where on the range of angles you want to settle, and determining whether you have a very good reason for settling very far from the middle of the range.

    You seem to be asking why Weaverbird's rig does not exhibit much balance area. The answer is simple. The internal layout of the boat meant that the mast had to be right at the forward end of a workable range. I still achieve low stress in the cloth; and I achieve zero stress in the hauling parrels due to not having any, just as with the SJR. The latter is simply because the battens butt against the after face of the mast, not because of the geometry of the sail. Having no hauling parrels has resulted in less stress on an ageing, weakening sailor.

    With more freedom over mast placement, she might well have been wearing a SJR, believe it or not. Made according to my own ways of doing things, of course, and having cast a seaman's eye over existing examples, particularly Amiina, and noted some areas where I believe that there is room for improvement. And that raises the question: why the need to be so prickly and unpleasant when someone tries to improve the breed? No single one of us has a monopoly on all the right answers.

    Last modified: 07 Jul 2021 21:54 | Anonymous member
  • 07 Jul 2021 13:39
    Reply # 10734568 on 461931
    Anonymous member (Administrator)

    Check that angle... (offset angle)

    Obviosly, it would be too much to ask for to produce mathematical equations covering the forces in a junk sail.
    Here I have cut some corners, and just drawn in three different junksails on the same boat. As for vertical forces, we have gravity and sheet forces as the worst ‘mast benders’.

    Take a look at the diagram below. I have drawn in a line between the mast top and the CE of each sail. As can be seen, the angles between that line and the plumb mast vary a lot ("offset angle"). My hunch is that the wider that angle is, the higher the compensating forces in the THP need to be to prevent the sail from falling forward.

    Obviously, the Ingeborg sail  -  here set extra far aft (normal balance  is 15-16% in her rig)   -  comes out not so well. Sitting this far aft, the THP and YHP will be quite taut. Luckily, by shifting the halyard’s slingpoint and the YHP well aft of the middle, the THP is still fully manageable, but on a big sail it would take a winch to deal with it.

    The as-built sail with 60° yard and 22% mast balance lives a much easier life. Here the THP has actually been omitted. The sail just rests on the upper batten parrel.  A true instamatic rig!

    Finally, there is the Amiina style SJR. This must be very easy to deal with, even with a very big sail.

    And then there are the sheet forces...
    It doesn’t take an Einstein to realise that the further aft the CE sits compared to the mast, the higher the sheet forces will be.
    The SJR comes out as a clear winner here as well.

    So why do I cling to the Johanna-style rig with 70° yard? I don’t. It is just that my boats’ preferred mast positions have dictated fairly low-balance sails. These sails may call for higher static forces on some parrels than a high-balance sail, but they are not extreme in any way, so are in no way show-stoppers.
    What would have been a show-stopper to me is if I had to constancy adjust the setting of the parrels when under way. As it is, I can mostly sail along with the tiller in one hand and a beer in the other.
    Good enough for me.

    Cheers,
    Arne

    PS: Stress in sailcloth.
    I cannot find any connection between aspect ratio, sail balance and stress in the sailcloth in my sails. The strong boltrope (rope or webbing), Hong Kong parrels and the other running parrels ensure that the sailcloth is only there to collect the wind and transfer the forces to the surrounding battens and boltropes. No need for tablings or strengthening patches, but a bit care should be taken to avoid damage from chafe and abrasion against hard or sharp bits, and a sail cover may be useful.



    Last modified: 08 Jul 2021 09:59 | Anonymous member (Administrator)
  • 07 Jul 2021 09:39
    Reply # 10733943 on 461931

    Wherever I post the question David, we need an explanation of how to use simple geometry and trigonometry to calculate the lower stresses you are achieving in your rigs, so that we can improve our rigs. Simply quoting the notes I printed of my experience is not enough, particularly as you do not use the key points they recommend.

    We need help to understand the basis of your statements as alone they do not add up.

    Cheers, Slieve.

  • 07 Jul 2021 08:45
    Reply # 10733848 on 461931

    Slieve, perhaps your latest posting might have been better made in this topic.

    I don't think a reply would serve any purpose here.

  • 06 Jul 2021 23:39
    Reply # 10733001 on 461931
    Anonymous member (Administrator)

    I know that some of you folks have made junksail models from string and battens only (no canvas) and hung them up. It appears that this exercise favours sail planforms with slightly convex luff to balance out the curve in the leech.

    However, there is a big noise factor in that equation  -  the sheet.
    I soon learned that the sheets wanted to have a saying, both in Malena’s blue sail, and in Johanna’s and later sails. If I set up the HKP for calm conditions while hoisting the sail, first time, it could happen that those diagonal creases re-appeared in one or two panels, once close-hauled in a breeze. Opposite, when running before, it could happen that a crease appeared in the opposite direction.

    Nowadays, when the THP-YHP-combination removes most of the loads on the HKPs, these will be easy to set up so that the sail stands without creases, both when close-hauled and when running before. The HK parrels should still be of a stiff halyard type, but 6mm will do fine  on sails below 50sqm.

    With Slieve’s über-clever combination of batten parrels and downhauls in his SJR sails, one can of course forget about the HKP, but that is another story...

    Arne


    Last modified: 06 Jul 2021 23:57 | Anonymous member (Administrator)
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