Flat, hinged or cambered?

  • 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)
  • 06 Jul 2021 22:32
    Reply # 10732864 on 461931

    Arne wrote, “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, with 60-70 degrees full-length yard (..basically the standard Hasler-McLeod sails with added camber...)? Should Zebedeeand Mingming II have their rigs remade?”

    David replied, “Arne, This is simple geometry and trigonometry, and I'm not going to insult your undoubted intelligence by giving lessons in it. However, you might well read chapter 2, page 6 of Slieve's writings, where he describes how he developed the SJR planform by getting his model to hang as naturally as possible:”

    David, you may not want to insult Arne's undoubted intelligence, but please explain the simple geometry and trigonometry to me and the other readers. I would like to see how you have confirmed that you have lowered the stress in the your rigs because I don't understand how you come to that conclusion.

    When I first posted the draft notes on the SJR you criticized every aspect of it without any knowledge or experience of it, to the extent that I had to ask you to remove you posting, yet now you are quoting my notes but still not following them to achieve the low stressed rig that can result. I need help with the simple maths to be able to follow and appreciate you postings.

    Cheers, Slieve.



  • 06 Jul 2021 11:21
    Reply # 10731283 on 461931
    Anonymous member (Administrator)

    David,
    the yard angles are just a function of the needed mast balance in the sail. With 70° yard and the slingpoint at 55%, the balance can be varied between 12 and 17%. With a 60° yard, the balance can be up to 24-25%. A sail I recently drew up with 20-21% balance was given a yard angle of 65°.

    Now I found a two-year-old study I made to see what yard angle was needed to have 25% mast balance. As can be seen on the diagram below, both sails set with a comfortable 10° halyard angle and with the slingpoint 5% aft of the middle.

    For my own use, on my last three boats, the required mast balance has been between 10 and 17%, so 70% yard has worked fine. A sail with 60° yard on Johanna would either have forced the sail too far forward, calling for a mizzen, or I would have needed an over-tall mast to keep the halyard angle within reason.

    Hong Kong parrels.
    I can understand that you had negative experience with these on your low-AR fanned sails on Tystie and Fantail (unless you had very stout battens). Such wide, low-AR sails with little balance are a challenge to make set well. The Johanna-style sails with parallelogram lower panels and vertical luff and leech are much easier to deal with, once the THP and 2/3-up YHP were introduced. After that, the Hong-Hong parrels have lived an easy, but still useful life. They keep these lower panels setting well even when the pull angles from the sheets varies.
    Now I looked up Tystie’s first sail, found in JRA-newsletter #38. The yard angle is a whopping 83° and the mast balance is just about zero. No surprise that you had to struggle with that (huge) sail. My Johanna-style sails are moderate, middle-of-the-road designs compared to that.

    Conclusion.
    There is no reason for blaming the Hong Kong parrels. On my sails, I just install them and then forget about them. I haven’t touched Ingeborg’s HKPs since 2019.

    Arne

    (PS: If I get the motivation, I may one day make two additional ranges of master sails; one with 65° and one with 60° yard angle to cover a wide range of mast balance needs  -  but that will have to wait...)


    Last modified: 06 Jul 2021 15:38 | Anonymous member (Administrator)
  • 06 Jul 2021 07:52
    Reply # 10730925 on 10728865
    Arne wrote:

    Then Ketil Greve took contact last autumn, in need for a sailplan for his new Kelt 8.50. The mast position dictated a sail with a high balance, around 21-23%. To achieve that, I had to remodel the top three panels of the AR=1.90 master sail so the yard ended at a 60° angle.
    As a result, Ketil, who made the sail himself, now sets it without needing a THP at all. I guess the upper batten parrel limits the forward movement. The halyard is next to vertical and the YHP is attached well aft of the middle. I sailed with Ketil after that little photo session. The sail went up and came down easily, and the lightly loaded Hong Kong parrels ensured each panel set well. A true Instamatic rig.

    My conclusion is that the finer the halyard angle is, and the closer the CG of the sail sits to the mast, the lower get the forces in the parrel pair; the THP and YHP.

    And yes, the top panels set just fine, both with 7-up and when 3-up...

    Arne

    So, Arne, you're heading in the right direction with Ketil's new rig. We're not really so very far apart, with your 60˚ and my 45 - 50˚. Could I urge you, please, to make this the standard geometry in all of your master sails, so that your audience of first time sailmakers are spared the trauma of having to wrestle with getting a rig with a 70˚ yard to set well?

    Just find a way to dispense with that invention of the devil, the HKP, and all will be well. Give me a moment to think, now, how could that possibly be managed? ... I know! Hinges combined with only lightly cambered panels! That would do the trick!

  • 06 Jul 2021 01:01
    Reply # 10730301 on 461931

    David quotes Slieve as saying, "One clear feature was that the pressures on the battens were lower with the low angled yard and high sail balance rig compared with a high peaked Hasler-McLeod rig."

    I completely agree with his point about balance, which is why I overrode David's opinion on this for FanShi's sail.  One thing that I do love about this sail is that gybing is painless, even with full sail.

  • 05 Jul 2021 15:20
    Reply # 10729217 on 10728919
    Anonymous member (Administrator)
    David wrote:

    It's a good state to find oneself in, to be content with one's rig!

    So now, put on a windvane and some downhauls, and go for a long offshore passage - and then come back and tell us whether you're still content, or whether actual experience has modified your conjecture!  :-)  


    Nope, I prefer pottering around on my home waters. It's as with music  -  taste differs.
    My sailing in Ingeborg is more about smiles than about miles...

    Arne

    Last modified: 05 Jul 2021 16:45 | Anonymous member (Administrator)
  • 05 Jul 2021 12:18
    Reply # 10728919 on 461931

    It's a good state to find oneself in, to be content with one's rig!

    So now, put on a windvane and some downhauls, and go for a long offshore passage - and then come back and tell us whether you're still content, or whether actual experience has modified your conjecture!  :-)  

  • 05 Jul 2021 12:01
    Reply # 10728885 on 10728832
    Anonymous member (Administrator)
    David Tyler wrote:

    Arne,

    ....

    As well as the stresses in the rig, there are the mental and physical demands on the stamina of the crew to consider. By your own admission, your sailing mileage on each outing is trivial, and so the work involved in keeping your rig set well makes trivial demands on your stamina. I ask you to accept that sailing continuously, day after day, through squally and variable conditions, one seeks to reduce those demands.

    No, of course the rigs of Zebedee and Mingming II don't need to be reworked, so long as their skippers are content with them. Martin is not.

    Mental and physical demands? What demands?

    David, you keep telling me about problems I don’t have:
    The procedure to go sailng goes like this:

    • ·         I hoist the sail, preferably with the sail spilling the wind.
    • ·         I use the YHP to position the yard so that the halyard’s slingpoint end up just aft of the mast.
    • ·         I give the THP a moderate tug, and off we go.

    There is no tweaking to be done with the parrels after that. The lightly loaded Hong Kong parrels sort out the setting of the lower panels. However, when I alter sail area, the YHP-THP should be dealt with. This is not critical, as it is more about cosmetics; getting the lowest batten sitting parallel  -  and a little above the reefed bundle. I doubt if this is much different from other rigs.

    I don’t claim that my rigs are perfectly in balance (only square-sails are that), but the remaining imbalance  -  a result of having a fore-and-aft rig  -  is easy to deal with.

    The only items I would add to make Ingeborg offshore-worthy, would be to fit a windvane and a couple of downhauls to let me reef while running before.

    As for loads on the yard, battens and sailcloth -  I have sorted out this a long time ago.

    Arne


    Last modified: 05 Jul 2021 15:24 | Anonymous member (Administrator)
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