Flat, hinged or cambered?

  • 15 Aug 2018 13:10
    Reply # 6574663 on 6574652
    Jami wrote:
    Arne wrote:
    If you just cut/copy and paste your first posting here over in your preferred Gallion thread, I will follow on by moving my answer  over to that thread. And then we just remove these last postings here.

    Arne


    Oops, I thought there was some kind of a more clever system for webmasters to move whole posts/parts of a thread to another...


    There is, but our webmaster cannot be on the fora 24/7. The point is that we can move/edit/delete our own postings, whereas he can do the same to all postings.

    Now, if we had some volunteer moderators to join the team and do this part of the webmaster's job, perhaps one in each continent to cover all the time zones - wouldn't that be a wonderful thing for keeping the fora tidy?

  • 15 Aug 2018 12:40
    Reply # 6574638 on 6574615
    Arne wrote:

    Moderation in all things,
    or...

    ..small changes can make a big difference.

    David,
    I can see your point in wanting a sail which is as balanced (weight-wise) as possible. Slieve McGalliard also has a focus on this. His Split Junk sails are both balanced for hoisting and lowering, but also come out with very light sheet forces.

    I haven’t had the same focus on that. When I looked at many Chinese junks (the real ones), it appeared that this didn’t bother them, so I just followed on.

    Arne, I haven't had any focus at all on weight-wise or area-wise balance (Slieve does, I agree). Because my mast is a little further forward than I would have liked, I have to set the sail well back on the mast, so that the tack is only just forward of the mast. Because the yard is short, there is no more balance area at the throat of the sail than with your sail at 13 -15%. My sail is about as unbalanced as it's possible for a JR to get. And yet it requires little thought and effort to set it well. It's all down to the yard angle and the shape of the upper panels.
    Last modified: 15 Aug 2018 13:15 | Anonymous member
  • 15 Aug 2018 12:22
    Reply # 6574615 on 461931
    Anonymous member (Administrator)

    Moderation in all things,
    or...

    ..small changes can make a big difference.

    David,
    I can see your point in wanting a sail which is as balanced (weight-wise) as possible. Slieve McGalliard also has a focus on this. His Split Junk sails are both balanced for hoisting and lowering, but also come out with very light sheet forces.

    I haven’t had the same focus on that. When I looked at many Chinese junks (the real ones), it appeared that this didn’t bother them, so I just followed on.

    However, Johanna’s rig (2002) ended up as an extreme case of broad chord and little balance, with AR=1.87 . To make it worse, the mast was too short for a decent halyard drift. The result was that the forces needed in the YHP and THP ended up quite high (though not needing winches). The AR=2.15 sail I built for my Oslodinghy, Broremann in 2009, gave some useful hints. Here the forces in the parrels were very light, or hardly needed. I thought this had with AR alone to do.

    When I made Ingeborg’s sail (2015), the AR again dropped to 1.90, and I planned to set it as Johanna’s sail, with about 10% balance. However, this time I had built a plenty tall mast, so the halyard could be moved 5% aft of the middle of the yard, and the YHP could be moved even further aft and up the yard.

    After two test trips I found that Ingeborg had too much weather helm, so I moved the whole sail forward to about 13-15% balance. This turned out to be a double success:
    The helm balance was improved, but surprisingly, the forces on the YHP and THP also dropped a lot. I still use them to position the sail and remove the diagonal wrinkles, but the forces involved are so light that I claim it is no longer a drawback of this sail planform.

    Arne

    PS: The only line I have to touch between reefing or un-reefing, is the sheet. I don't need to alter the set of the YHP and THP when falling off to a run or heading up for close-hauled sailing. What more can one ask for?

    PPS: The throat hauling parrel, THP, is just another word for a luff hauling parrel, LHP, after having moved it up a couple of battens. 


    Last modified: 15 Aug 2018 15:05 | Anonymous member (Administrator)
    Merged topic from TECHNICAL FORUM: 15 Aug 2018 20:49
  • 15 Aug 2018 09:40
    Reply # 6574492 on 461931
    Annie wrote:

    I'd love to hear, too, Arne.  Alan (ZBD) and I both feel that camber puts a lot more stress into the sail, but as he sails engineless and, like most Trade Wind sailors, doesn't just sit in an anchorage and do nothing between passages, but goes exploring, he reckons the trade off is worth it.

    I feel that camber in itself obviously must increase the stresses in the sail, simply because it's developing more power, but that it's easy enough to build a sail strongly enough to bear them; but I also feel that that's not the important point, which is that planform is the factor that mostly determines the loads in the sailcloth, as well as in the running lines.

    Articulated battens, if simple and stout and in the right place, in combination with flat sails are probably almost as robust and stress-free as a flat sail.  I'm not sure that I have the skills to make the 'hinges' however and I really can't afford to farm things out.

    Unfortunately, two hinges per batten require minimal balance area to articulate reliably, and that leads to greater sheet loading. You can't get something for nothing! SibLim's sail as currently drawn probably has too much balance area for two hinges to be an option, but a single hinge at 40% of chord, combined with some sewn-in camber ( more sewn-in camber than I have, so made with tucks, broad seams or shelves) is a possibility, and I would say, a good and effective one. Hinges with a flat sail are not particularly effective, as it's hard to get enough camber and that camber is not in a good shape. Sewn-in camber alone brings sail setting problems along with it. It's the combination of some of each that I've found to be more than the sum of its parts.

    Farming out the hinges is not a cost effective option. I've found that they need to be turned from Nylon 66, with 30% glass reinforcement, and that's easy enough to buy, but the taper turning takes a lot of time and simple lathes don't have the ability to do it automatically, so I have to stand there winding the compound slide by hand. If you get charged by the hour for somebody's time, it's not worth it. But for SibLim, I'd do it, if you want to go this way. On my mini lathe, I just have enough capacity to turn hinges for 38mm tube.


    Last modified: 15 Aug 2018 10:18 | Anonymous member
    Merged topic from TECHNICAL FORUM: 15 Aug 2018 20:49
  • 15 Aug 2018 09:00
    Reply # 6574458 on 6573795
    Arne wrote:

    Flat or cambered for deep sea voyaging?

    Time for a revival of this old topic.

    Nowadays, it doesn’t seem to be controversial to put camber in junksails meant for coastal cruising. However, from time to time the question about flat versus cambered sails still appears when the matter of ocean travelling is up. The boat of the month is currently Chris Gamble’s 34’ schooner. He chose to go for flat sails and seems to be happy with that.

    Now, today, Asmat Downey reports that he has returned from a big Atlantic tour in his Wylo 32, Branwen, schooner-rigged with cambered panel sails.

    For the sake of science, would you Asmat be so kind and answer these two questions (apart from writing a good story for the Magazine)?

    1.      Did you during the voyages have any problems which were specifically connected to having camber in the sails?

    2.      If you were to repeat your voyage with the same boat, and knowing what you know now, would you make the new sails flat or with camber in them?

    Anyway, welcome back!

    Arne

    Let's be clear about this, Arne. Deep sea voyaging per se is not the thing that determines whether camber is a good thing or not. It's where on those deep seas that you are voyaging, and whether you have an engine.

    Chris Gamble was on a simple mission, to get from Europe to NZ. This is a voyage where downwind sailing is going to predominate, with trades except for the first bit down to Spain, Panama to Galapagos and Tonga to NZ. He had a good seagoing boat with an engine. His decision to use flat sails was the right one. But now, consider an engineless junk doing the same trip. Considerable windward ability is needed to get through the passes on the leeward side of the atolls against the outflow, for example. Considerable windward ability plus a lot of patience is needed to sail from Panama to Galapagos without an engine. And then there's the ITCZ. By its very nature, it's easy to sail into the middle, but hard to sail out of the other side. An engineless junk will need full camber; a junk with an engine will do better to motor-sail through the fickle, light or non-existent headwinds, whether the sails are cambered or not. A small efficient diesel plus a large tank of fuel is a key component of a stress-free cruising boat.

    Now consider my final two ocean voyages: singlehanded from NZ to Alaska, and from Canada to NZ. The first with a fantail-pattern sail - fanned planform, very high peaked yard, straight battens, some sewn-in camber particularly in the lower panels; the second with the sail salvaged from my failed attempt at a wingsail - low peaked yard, battens with a single hinge, flat cut sail.

    The first voyage is one in which windward work predominates. Indeed, many American sailors view it with such trepidation that they will not attempt it in their bermudan-rigged boats. I had no difficulties with windward ability, but it was hard physical work. Why? Because of the high peaked yard and the associated high loadings in the YHP and LHP. Not as hard as sailing a bermudan-rigged boat on the same passage would have been, but harder work than sailing a junk rigged boat needs to be. I build my sails strongly, and this sail was made from Haywards cloth, so breakdown of the cloth around the throat area did not happen, as it did in Fantail's first sail. This was due largely to the cyclical diagonal loadings that occur in the throat area of a high peaked sail - not an issue in a lightly used coastal cruising boat, but needs to be taken seriously and guarded against in an ocean cruiser, with plenty of reinforcing patches.

    The second voyage also contains plenty of windward work, but is more of a mixed bag. Some camber is certainly desirable, though. The physical work was very much less demanding, with the low peaked yard. This matters a lot, with an ageing singlehanded crew. I made the voyage quite fast, because I was able to keep up with sail changes without exhausting myself. I had been challenged to get to NZ in time for Annie's 60th birthday party, and only missed by a week, due to strong winds and washing machine seas off Tonga that made me need a rest, not through lack of windward ability.

    Do you see, Arne? That last ounce of windward ability, so important in racing and for having fun while sailing around Stavanger Fjord, is only occasionally of very great value in ocean cruising, and can be substituted with a turn of the engine start key. 24/7 ease of sailing matters more. A small crew has limited stamina, and an exhausted crew makes bad decisions. A docile rig with little camber is better for motor-sailing, too, and that matters more when cruising in tidal conditions than it does in Stavanger Fjord.

    It was the experiences of those two voyages that were - not a road to Damascus conversion, exactly, but more a crystallisation of my thoughts, when it came to deciding what kind of rig to put on Weaverbird. The similarities with Tystie's present rig show that there is a clear line of development, yet they are not all that similar when you look closely.

    To list the main points of Weaverbird's sail design:

    1. 45˚ yard angle - less than H&M and Arne's planforms, more than Van Loan's (from memory) and a yard that is shorter than the battens.
    2. parallelogram lower panels, just like all JR planforms except the totally fanned ones.
    3. Longer luff lengths on the upper panels, so that the fanning effect is much less distinct a feature than on H&M and Arne's planforms, but is still there.
    4. Two hinges in all the  battens, but with the angle of articulation reducing from 20˚ to 10˚ in the top batten (for reliability of articulation).
    5. A minimal amount of barrel-cut camber in the lower panels - 45mm of round, in a chord of 3360mm. It's hard to get a deep camber with hinges alone, and this addition of a little camber in the panels increases camber from 6% to 9%.
    Would I put Weaverbird's rig on an ocean cruising boat? Yes, absolutely. In two seasons, of four full-time months each and a total of 3300 miles, it's proved sound and reliable in all kinds of conditions. Just as much, and perhaps even more to the point for cruising is that it's as effortless and thought free a manner of sailing as is possible. Arne's postings on his rigs are often about how you need to do "thus" and "thus" to the YHP and THP and LHP and HKP to get them to set well. My YHP is redundant under full sail, and only lightly taken in when deeply reefed. My LHP (no THP necessary) can be easily taken in with one hand whilst steering with the other. The sail sets well, with little tweaking and conscious thought on my part. Why? Mostly because of the yard angle and its shorter length, and the particular shape of the upper panels, and not because of depth of camber, or the way in which camber is added. This is what truly matters when ocean cruising. On a dark moonless squally night, being able to reefing and unreef, and knowing that your sail is well set even though you can't actually see it, is worth more than that last ounce of windward ability.
    Last modified: 15 Aug 2018 10:07 | Anonymous member
  • 15 Aug 2018 08:11
    Reply # 6574408 on 6573826
    Arne wrote:

    The top panels (at least on my sail) are quite efficient and they are cut almost flat. My guess is that they get their surprising efficiency from the little camber in each panel, combined with a bit twist in the sail. 

    On my Galion's sail there seems to be a dramatic change (more dramatic than the amount of sail area reduced) between the windward ability - both the angle and the power - when I reef from three panels to two. In stronger winds I can happily tack against the wind on narrow passages with three panels, whereas two panels makes this impossible - this is also when the wind would otherwise make me want to drop to two.

    So far it seems better to stick with three panels and just be super careful at the helm "dinghy style", pointing the bow almost to the wind on a puff. 

    I aimed to 2%, 4% and 6% on the top panels, but I havent't measured if this is the case in real life. The camber is visible all the way to the top, though.

    The shape of the Johanna-type sail changes drastically when one drops to two panels. Do you think this is the most significant reason for the loss of angle annd power?

    Last modified: 15 Aug 2018 08:13 | Anonymous member
  • 15 Aug 2018 07:29
    Reply # 6574370 on 461931
    Annie wrote:

    I'd love to hear, too, Arne.  Alan (ZBD) and I both feel that camber puts a lot more stress into the sail, but as he sails engineless and, like most Trade Wind sailors, doesn't just sit in an anchorage and do nothing between passages, but goes exploring, he reckons the trade off is worth it.

    I want to achieve a cambered sail that has no loadings on the running lines, like a flat sail.  I really disliked the force required on the LHP to pull out the creases on Fantail's sail.  Paul's foresail on La Chica only required the slightest tweak.  David and I are hoping that SibLim's sail will be the same.

    The Aero rig has minimal stresses, but on the other hand it has lots of little bits that can fail, which would be tricky to fix on a small boat at sea.

    Articulated battens, if simple and stout and in the right place, in combination with flat sails are probably almost as robust and stress-free as a flat sail.  I'm not sure that I have the skills to make the 'hinges' however and I really can't afford to farm things out.


    Merged topic from TECHNICAL FORUM: 15 Aug 2018 20:49
  • 14 Aug 2018 22:35
    Reply # 6573826 on 461931
    Anonymous member (Administrator)

    Annie,
    I trust you move your last posting over here.

    I have to say that the load on the YHP and THP of Ingeborg's sail is quite light, unlike the forces I had in Johanna's sail. 

    On Johanna the sail had to be hauled aft to minimum balance to avoid lee helm. In addition, I had cut the mast about 50cm too short. This forced me to move the slingpoint on the yard forward to the middle. All this lead to quite high control forces in the parrels.

    On Ingeborg the mast is plenty tall enough. As luck would have it, she initially turned out to have a bit too much weather helm, so the sail was moved forward to 13-15% balance. This actually is a more natural position for the sail with 70degrees full-length yard. With the slingpoint moved about 5% aft of the middle of the yard, the resulting  forces in both the YHP and THP are, as said, quite llight.

    The procedure now after raising the sail is to gently bring the slingpoint forward to about 20cm aft of the mast with the YHP, and then give the THP a tug, not very hard, and the sail is fine.

    Arne

    PS: I don't think that hinges are the way to go  -  been there, done that: With the hinges installed, the flat sail became a completely different animal  -  a lot more powerful, and I guess that stress rises with the increased aerodynamic forces.

    My prescription is to make the sail with cambered panels and then reef earlier. The top panels (at least on my sail) are quite efficient and they are cut almost flat. My guess is that they get their surprising efficiency from the little camber in each panel, combined with a bit twist in the sail. The powerful lower panels can be stored safely in the lazyjacks from F4+ and upwards. They are still very nice to have in light winds.

     

    Last modified: 15 Aug 2018 08:59 | Anonymous member (Administrator)
    Merged topic from TECHNICAL FORUM: 15 Aug 2018 20:49
  • 14 Aug 2018 22:26
    Reply # 6573814 on 461931

    Dammit, Arne.  I've just posted a response on an almost identical thread.  I think they should be combined together, and I've asked the webmaster to see if he can.  It's probably one of the hottest topics in JR and should be concentrated on one thread so that people can easily find the information.

    Merged topic from TECHNICAL FORUM: 15 Aug 2018 20:49
  • 14 Aug 2018 22:22
    Reply # 6573813 on 461931
    Anonymous member (Administrator)

    Argh, Annie,

    I just moved my posting over to that other thread within the Technical Forum!

    Arne

    Last modified: 14 Aug 2018 23:54 | Anonymous member (Administrator)
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