SJR - A wider discussion on future possibilities

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  • 15 Dec 2021 23:04
    Reply # 12195484 on 12194095

    Copied from other thread, where it appeared that it might be useful to give some background information. I can see where some are coming from, but would like to add a note of caution to some of the ideas which have appeared here.

    The original Poppy rig, and the quite swift drift towards the Amiina Mk2 rig were no accident. They are out in the public domain and if anyone wants to modify them that is their own free choice, but the resultant rig will ideally have its own name/ label to identify it from the rest. The reason I suggest this is that experience has shown that those who have faithfully copied the original ideas have achieved results similar to the originals, and a number of those who have deviated any distance have later approached my off line to try and find out why the results have been poor.

    A lot of thought went into the problem of improving the windward performance of the humble junk rig, even though the basic principle of obtaining a good Lift/ Drag (L/D) was fully understood. Lift was easy, but total drag is made up of a number of different elements, induced drag, form drag, skin friction and others, and the reduction of these may well be more important than the increasing of the lift. Poppy's rig was a 'proof of concept' effort, with no guiding light, and a big leap of faith. As it was being built many little problems had to be solved, and a lot was learned.

    One aim was to use conventional sail-making techniques so that the design could be built by commercial sailmakers, hence the use of round and broadseam for the main panels, but it was clear that to get the envisaged camber shape into the jibs would require a seam running into the top and bottom front corners with well tailored taper included. The flat shelf foot was considered, and eventually developed into the new idea of the angled shelf foot to try to control the shape of the leech area at the same time. Even with this original idea I feel there is still work to be done to find the best camber shape. The 45º shelf made sense as the square root of 2 is instantly recalled.

    As the rig was being built the problem of shaping the panels became clear. The shape of the clothes for a jib with different chords at head and foot, and with battens that are not parallel were calculated on a spreadsheet, but still required 'adjustment' as they were sew up. They are not an ideal challenge for a first time sail-maker. Working on my own I found it an interesting exercise, and the Poppy rig has may experiments sewn it, as part of my education.

    I was confident that the rig would perform well, but even so, was surprised at some of its strengths. It took some time before I could understand where all the performance came from. When the first sailor with junk rig experience sailed it he went away with a silly grin on his face muttering, 'I must have it', and a week later phoned me to say that he had just bought a sewing machine, and could he have the design for his boat next week, at the latest! There was no way I could have talked him through the building of the Poppy rig over the phone, so I had to over draw the profile to make it a practical proposition. We worked well together over the phone, and he built a successful sloop rig to replace his previous 2 mast set up. Since then all the rigs I have drawn have followed the 'more angular' shape for the same reason.

    The Amiina Mk1 rig was my first attempt to provide the design for a commercial sail-maker to build. Unfortunately we did not get the sail area right as the racing brigade would not admit how the Splinter 21 rig had shrunk. It was not helped by the efficiency of the SJR so a smaller rig was required. Even so, when I asked Edward to check some measurements on the Mk1 rig I found that the sail-maker had not accurately followed my numbers and had variations between identical panels. The Mk2 rig was therefore going to be home built to avoid this problem. I also wanted to simplify the design as by that time I was getting quite a few questions off-line from those trying to build the Poppy style rig and getting stuck. On the other hand, Edward reasoned that if the split added performance then why not split all panels. He got his split, but I still do not recommend it as apart from the camber shaping problems it introduces a potential problem with luff and leech lengths in the top tapering panel, where if the jib is moved fore or aft it can result in slack luff or leeches. The Mk2 rig was an attempt to make a practical rig for the average experienced sailor to build, and still retain all the key features that I believe effect the performance. Those who have copied it seem fairly happy with it. KISS refers to building as well as sailing and low stress.

    Prettiness, which is in the eye of the beholder, comes at a price. The selected yard angle, aspect ratio and balance all have a reason. They have already been proven in practice. The angular shape simplifies construction. The reduced number of panels is no accident. Experience with the rig suggests that there is good flexibility in wind range for each step in sail area. On Poppy I always reefed in 2 panel steps, so why not simplify the build?

    I hope this is of some help.

    Cheers, Slieve.

  • 15 Dec 2021 21:10
    Reply # 12195282 on 12194095
    Anonymous member (Administrator)

    Thanks Jan, I never figured on being "chairman"  - just want to provoke some discussion in order to get ideas collected and documented - especially those of the "boffins" as you have aptly decribed them. Don't worry about the boffins - they are intellectually honest to a fault, and honest expression can be excused for stretching the bounds of civility slightly at times - we don't want all this to be too bland, do we?

    A proper catcher, as designed by Slieve, doubles very conveniently as a sail cover. You just uncouple the halyard (or not, if you want to allow for it) and fold the top over itself and then with a zip or  velcro, close it off. (See Slieve's notes, in the documents section of the website for his design).

    I didn't bother taking it quite that far on my little trailer boat because it doesn't get left on a mooring anyway. 

    What I have done instead is use it as a convenient wrap for the sail and battens - it allows me to lift the entire bundle up (using the halyard, which I unclip and shift to a lifting point on the catcher itself) and using the purchase of the halyard I can effortlessly lift the bundle, unclip the lifts and then swing it into the boat (for road transport) or out of the boat (if I want to take it out). It keeeps the bundle togther, including the demountable double sheeting system, and reduces setting up and putting away times to minutes, so quite convenient that way too - it keeps it all together and in some sort of order. That's important for a junk rigged trailer boat, unless you like to spend hours messing about at the launching ramp.

    My sail catcher is set up in a slightly simpler (and I think better) way than Slieve and Edward have done, and I use no lazy jacks. It just clips onto two pairs of judiciously placed lifts. I have a feeling its better if the lift attachment points are on the catcher itself, rather directly on the catcher battens. With a heavier bundle, some thought should be given to spreading the load out a bit. If you attach directly to the catcher battens, this spreads the load nicely - but I think requires heavier catcher battens. By attaching to the catcher itself I seem to have got away so far with fairly light catcher battens, which then only mainly have to support their own weight and perform the task of keeping the edges straight and open. In practice, I guess the battens do share some of the load, but don't have to carry it all.

    I never thought about windage, though I have sailed at a couple of knots in a strong wind (on a broad reach) under fully lowered sail, and I suppose the sail catcher contributed to that. I don't think I would have broad reached under bare poles. So there's a thought - its not windage, its the ultimate storm sail !

    I can't see any reason why you couldn't use mesh instead of fabric - but you would still need four stout attachment points, which transfer the load to the lifts, and a way of attaching two parallel "catcher battens" - and the entire affair, however you make it, has to be strong enough to reliably carry the weight of the bundle, as the sail catcher also acts for the essential mast lifts and aft lifts, without which a junk rig  won't work - so you don't want the sail catcher to structurally fail. Also, ofcourse, with mesh, you get no ultra violet protection, or protection from anything else which might damage or dirty the sail while it is furled - and I doubt if it would reduce the windage much, compared with fabric, especially considering the windage presented by a naked furled bundle anyway. (When sailing, it just sort of becomes part of the lower sail and only a real purist would worry about windage in that situation). Also, my sail catcher is a somewhat bulky and over large affair - it was my first attempt and I am  not an expert with the sewing machine. I think it could have been tailored much better, made smaller, tidier and neater and in that case I don't think windage would be an issue at all.

    I spotted this on Trademe last night.

    The bermudan (or gaff) sail (being a symmetrical setup) lends itself even more to a sail catcher/sail cover. This owner doesn't seem to realise the mass of lazy jacks could be greatly reduced, and if anything in this category was attached to the catcher itself (rather than the boom) it could be closed off completely and probably perform its most useful task as a jiffy sail cover. Putting a conventional sail cover on is a pain in the neck, especially if you have to work around lazyjacks - this way its almost instant. I had a dream of doing something like that for Havoc (a gaff scow schooner with lazy jacks) many years ago, but never got around to it.

    David has plenty of experience with sail catchers and has a different opinion about them. He might add to this, with ideas of his own. Marcus R doesn't like them at all, wouldn't have one for quids, he told me. I think, as Arne pointed out, with SJR you really have no choice, because of those pesky jibs. I'll bet David or Arne will now come up with a "better" sail catcher! (But I'll stick with mine, its an asset).

    Hey, I just had a "thought". Why not design the sail catcher to incorporate a proper triangular storm sail, rolled up inside, out of sight but ready for use. Switching the halyard from the junk sail to the storm sail with a jiffy clip of some kind. Then you can have a decent, stout, flat cut storm sail - and let the top triangle of your junk sail be light and well cambered, as it really should be. Its always seemed a shame to me that the junk rig suffers from having to have just the sort of topsail which performs worst in light airs.

    As a matter of fact, my bulky sail catcher is big enough to accomodate a pair of oars, a yuloh if I had one, and a long boat hook. 

    Last modified: 16 Dec 2021 08:31 | Anonymous member (Administrator)
  • 15 Dec 2021 19:29
    Reply # 12195008 on 12194095

    Well done Graeme chairing this thread, it's very interesting and I'm sure I'm correct in saying that many members are following this closely even if not chipping in and would be delighted if the boffins could keep it civil and keep it technical! 

    Just to throw the discussion off on a brief tangent; It seems a sail catcher is essential on a SJR. Has anyone tried using one made out of heavy duty netting (like a piece of old trawl netting) rather than solid fabric to reduce windage? Or does the sail catcher double as a sail cover? 

  • 15 Dec 2021 11:37
    Message # 12194095
    Anonymous member (Administrator)

    It is of great interest to me that both Arne and David have suggested a move back to the Poppy design (which remains a classic in my mind, and probably the initial inspiration for most of those who have gone down the SJR road.) Even more interesting to me, is that Arne’s current proposal is evolved to the point where it has lost the soft beauty of the Poppy sail – and now almost (not quite) resembles the Amiina Mk1 sail !  

    In other words, Arne and David may be marching the evolution of the SJR backwards towards its starting point, with more panels, lower aerodynamic balance and greater rise-angle of batten. I imagine this will not please Slieve, who has been leading the way in the other direction. But that’s OK – we are always going to need "horses for courses" - and I don’t mean “backwards” in any derogatory sense, only in the sense of time. I make the point that both of these earlier SJR rigs worked well, and I have no doubt the recent suggestions of Arne and David would work well too, and if one proves better than the others, it is likely to be by such a small amount that we may never know. Personally, for my purposes I can find no fault with the Amiina Mk2 rig and I think I’ll be sticking with it. In fact all the cambered junk rigs work so well, that no-one yet really knows which is best. (I’d put my money on David’s recent junk wing sail, but the question of which is the highest performing junk plan form is a whole ‘nother question, probably as potentially fruitless as the dinghy design competition and for the same reasons. Horses for courses, remember?) Discussions generally don’t revolve much around actual performance, they all perform well these days, but more around questions of handling, rigging detail, sail making, mast placement, structural issues etc.

    I have taken the liberty of adding two more sail plans onto Arne’s “Three split junk rigs” and if Slieve gives his permission I will put a larger version and hopefully open up a new discussion. It rather strikes me as an illustration of an evolutionary process.  (You are going in the right direction Arne - just two more iterations to go, and you have almost caught up!)

    (On this illustration the Amiina Mk1 sail (second from the right) is not to the same scale as the Mk2 -  its zoom-fitted here for mast height and to illustrate shape. In reality it is a little larger than the Mk2 sail (on the far right) and I don’t know the numbers, only the shape. Cambers and “sheeting angle” are different too – these also are evolving and need considering in another discussion. Also I shifted Arne’s ruler down to an approximate deck position, instead of at the tack.)

    Marcus’s question: what is it which actually defines the Amiina Mk2 rig is a very good and profound one, and I would like to have a crack at answering it some time, unless Slieve himself wants to do so, which of course would be much better.


    I would like to challenge your five bullet points regarding the Amiina Mk2 sail:

    • ·        The increased size panels will see more loads in the cloth. Does that matter? Are the loads all that high anyway? Can’t the sail still be made strong enough? What about the load on a Bermudan genoa? Also, would you not agree that there is less loading on a low yard-angle sail?
    • ·         Fewer battens will have to share the same total load. Does that matter? Can’t the battens just be designed sufficiently strong? The difference can’t be much, can it?
    • ·         More vertical tension is needed to keep the luff taut. I think you are actually wrong there. The luff should not be taut (in sense of a Bermudan luff being taut). The luffs are cut straight, not curved for camber, so no need to have them taut. Just enough tension is required to keep the luffs more or less straight, and it isn’t very much. And not only that, with the running parrel downhauls (part of the McGalliard SJR package) that’s about the only tensioning of any kind required to make the sail drape correctly, provided the hoist point is sufficiently high – a major advantage of McGalliard-SJR design in my view.
    • ·        Reefing is done in much bigger steps. Correct. You only have a 4-speed gearbox, instead of 6. It’s a valid criticism, though for me it is only a minor issue. 4 is enough for the sailing I do anyway. I am not a racer.
    • ·        Better lazyjacks or sail catchers are needed to collect the wide panels. No. Lazy jacks won’t do it. For SJR you have got to have a better way of muzzling the jibs. Actually, the sail catcher works so well I don’t know why it isn’t used on all rigs.[Belay that. I don't think a McGalliard sail catcher will work with standing batten parrels. It works fine with Slieve's running batten parel downhauls.] I see it as an asset. In addition, if it is rigged properly, to a large extent it keeps lifts away from the belly of the sail as well as eliminating the need for lazy jacks. Anyway, for the Amiina Mk2 SJR the sail catcher should be considered part of the package.

    Oh, and Arne, I forgot to mention - your hybrid Poppy/Amiina/HR is just another example of your wonderful ability to generate new ideas. I am waiting Slieve's reaction with interest. It could be "just what the doctor ordered" for Marcus. I was interested to see that the Amiina Mk2 sail at this scale (estimated 35.4 sq m) is actually greater in area than your higher yard angle hybrid - but you have got away with a lower sling point, so to be fair, if you scaled your sail up so the sling points were equal, you'd have the sail with the largest area in that suite of five SJR sails with identical sling points. The unknown (for me) is how it will drape, will it need a suite of parrels to hold it in place, as well as downhauls - or will it need only the spanned running parrel downhauls which is one of the special features of the Amiina sail. That would be a crucial requirement for me. Otherwise, I'd rather have a Johanna sail, which I think Marcus should also consider.


    (1) I would be interested if you would expand a little the notion of modifying the Amiina mk 2 sail by adding an extra lower panel. I would be keen to hear Slieve’s comments on that, also, of course. This will not suit me (and I don’t think it will suit Marcus) but it may well be valuable food for thought, for anyone converting a hull which calls for a very tall, high aspect ratio rig.

    (Its an idea which I had considered a couple of months ago for an unsplit mizzen sail (an Amiina-shape Van Loan type of sail) to go onto a proposed ketch rig for my scow project – I was mainly looking for ways to increase the area of the mizzen, without adding to the chord. (I’ve got a problem: I now fear that my CLR is too far aft – I’’ll be asking for advice about that at a later time.))

    I doubt if I will go ahead with that rig, I am leaning more towards a single mast rig, but David’s comments have sparked my general interest).

    (2) Regarding your proposed Poppy sail on SibLim 10m. I think the mast is a bit short. The 21 degree halyard angle may not be enough to get the full benefit of the Poppy sail - and this is exacerbated by the forward rake you have given the mast. I would dearly love to have forward rake. Its an aquired taste - I had previously fallen in love with the aft raking masts of L Francis Herreshoff and other American designers, but after Annie explained the advantage to me of forward rake, on one occasion, I began to change and now my heart leaps when I recognise a junk in the distance by the Chinese rake of its mast. But I wouldn't put rake on a McGalliard SJR, without a VERY good reason. Now you probably know all this, and I should probably leave it to Slieve - but I am going to risk "teaching grandmother to suck eeggs".

    One of the exquisite features of Slieve's designs - and the factor which most attracted me, was the absence of any need for horizontal-pulling running or standing parrels, a property which is built into the geometric outline of the sail - you will recall Slieve's description of how he first designed the sail outline with dowel rod and string. Looking at the stark simplicity of Amiina 2, nobody would guess how much might be lost by tinkering with the proportions. There is always talk on the forums about adding this parrel or that parrel and I got so confused about all these parrels that I nearly gave up on junks altogether. There doesn't seem to be a word in the junk vocabulary for it, so I invented one which I have used occasionally - that is, "drape". It means in this context, the ability of a soft fabric to hang the way you want it to, with very little outside interference other than gravity and, in the case of a sail, the aft-seeking horizontal component of the sheeting forces). If the proportions of a high-balance low yard angle sail are just right, and the sling point is high enough  (or more precisely, if the mast/halyard angle is low enough) the sail will automatically drape almost without any of the usual suite of parrels which most people seem to need, and the forces needed to make the sail drape correctly are quite small, almost (but not quite) entirely vertical. It then becomes practical to dispense with the usual parrels and use Slieve's spanned running parrel downhauls which to me seem so much more elegant and simple - I realise it still means at least two or three lines to adjust when reefing - nothing really saved there - but all they need is a tweak - and you have to have the downhauls anyway, or otherwise how do you keep the jib luffs straight? So, I think your proposed rig  might possibly need the suite of what I call old fashion parrels, including standing batten parrels - because you are going to be fighting gravity with the foward raking mast, plus the pull of the horizontal component of your 21 degree mast/halyard angle, in addition to needing the downhauls to keep the jib luffs straight - perhaps the worst of both worlds, so to speak. It wouldn't surprise me if you have already thought all this through, and have an answer I hadn't thought of. In that case I'll learn something. But to anyone else, I would say: if you want a McGalliard SJR such as a Poppy or Amiina rig, don't make arbitrary small changes - you might end up with something that doesn't work as well as it should. If it was anyone else, I would advise them to raise the masthead a little and straighten that mast - or, if you prefer to use the conventional system of parrels, consider redesigning the sail outline somewhat, so that you have an entirely new sail design, with perhaps just the Poppy "look". I don't know what Slieve is going to say, and I hope I am not "getting above myself" even more than usual  - but there's some food for thought anyway.

    Edit: another thing, I had forgotten. Edward should be asked to hop in here too - he knows more about the performance of the Mk2 rig than anyone - and can also advise in practical terms, the differences between the Mk1 and the Mk2 - a matter which should be of great interest to all of us. I do hope Edward sees this, and feels like adding his thoughts.

    Last modified: 16 Dec 2021 22:47 | Anonymous member (Administrator)
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