SJR - A wider discussion on future possibilities

  • 17 Dec 2021 01:43
    Reply # 12197929 on 12194095
    Anonymous member (Administrator)

    Hi Arne - yes, your terminology "slingpoint" is correct and mine was wrong, I have gone back and changed it.

    Also you are right, the yard slingpoint will probably be about the middle of the yard on Amiina Mk2, with, of course, allowance for fine tuning of the slingpoint position which will be expected, in practice.

    Mast/Halyard angle: My concern was, and I did use the wrong words - the point at the mast where the halyard begins. That's the point which needed to be shifted up a bit, to get the smallest possible angle between the halyard and the mast. I don't know what that angle should be, and I think you know better than me about that, but I did find by trial and error that the masthead point where the halyard starts has to be at least as high as the peak of the yard, and higher is better. It wouldn't surprise me to find that this rule of thumb applies to all low yard-angle rigs, but I only know about the Amiina Mk2. The higher the halyard crane, the lower the mast/halyard angle, and as you know, its that angle which is ultimately what gives that undesirable forward-seeking component of the halyard force on the rig, when it is fully hoisted. To me, your drawing looks better now. I am just documenting it, I realise that Arne knows all this.

    Forward rake of mast: For people with forward sloping masts, that critical angle we are talking about is the angle between the halyard and the vertical, actually (not the angle between the halyard and a forward leaning mast). A forward leaning mast exacerbates the halyard angle problem, and although it is a desirable and endearing feature, I don't think it suits SJR unless one is willing to dispense with Slieve's parrel system and revert to a suite of conventional parrels  - of which I have virtually no knowledge so can't comment other than to say it is then no longer a McGalliard SJR, it is something else, (hopefully, even better).

    You can count that as a disadvantage of the McGalliard SJR if you like, if you tend to sail in rolly-polly conditions when the bundle won't lie quietly in a calm or near calm. Annie explained to me one day, that if the mast slopes forward, the rig will swing out to leeward and tend to stay there quietly rather than slamming back to central all the time which will happen with an aft-leaning mast - this happens even with a bermudan rig and a vertical mast, but with all the weight of a Chinese rig with all its battens its more of a consideration. I guess those old Chinese shipwrights knew a thing or two about the junk rig.

    For Marcus: No rig gives you every advantage and you go crazy trying to tick all the boxes. With SJR you don't have the luxury of a forward raking mast, and thats just something you have to forgo unless you want to dispense with one of the advantages of SJR which is the potential for minimal horizontal forces on the rig and the ability to use only the McGalliard system for holding the sail to the mast. Its a trade-off. I wouldn't want to over-sell the "less parrel stuff" advantage - most people seem perfectly happy with conventional rigs and for me its not a big deal, just my own personal preference. I wish I could have my cake and eat it too - I have come to just adore the look of a forward rake.

    Anolther disadvantage of the SJR, which is closely related - or, should I say, another potential feature which the SJR does not have, is the ability to adjust the drape of the sail fore or aft while you are sailing, to get the balance just right and take a bit of load off the helm. With SJR once the mast is in place you are stuck with what you've got. You can't rake the mast forward, or back to vertical, to make a permanent improvement to helm balance, and you can't sling the sail forward or backwards on the mast to make a temporary adjustment to helm balance. People with contiguous rigs do have that liittle advantage if they want to mess around a bit with hauling parrels, which you won't have with SJR. Some people have favourite positions for the sail, depending on whether on the wind or off the wind. SJR can't do that. I just point that out to explain why there is no "BEST" rig, they all have their good points and a lot of it is just personal preference - especially if high performance is not your priority, as David explained to you.

    For Arne I wonder how the hybrid HM/SJR will drape. I note the advantage of your higher yard angle (more sail area or shorter mast, depending on how you look at it) but there is more to getting the sail to set nicely where you want it than just the mast/halyard angle. Would you expect to use Slieve's system of spanned running batten parel downhauls - or would you expect to use the conventional parrels as per your Johanna rig, to hold the sail in the position you want? I'm sure one system is as good as the other, but I would hate to have to use a hybrid combination of both. Whatever, I think the SJR panels are each going to need a light downhaul, just to keep the jib and main luffs more or less straight, so I am waiting with interest to see what you have in mind here. 

    For David ditto, same question as posed to Arne, and even more so with your shortish forward raking mast on your proposed Poppy-Siblim hybrid. No-one has answered this question yet.

    Your excellent points about "planform" are only from the point of view of the sail-maker, important though that may be. If we are seeking better performance, are there not aerodynamc matters which also need to be optimised? Also I think you have glossed a little too quickly over the issues facing a first-time sailmaker. One of the most important values of the junk rig is that it is open to DIY and long may it remain so. Starting off with something smaller is always better for the beginner, if there is the opportunity. But is 50 sq m really too big for a first time sailmaker? Aren't there a few counter examples out there? If it is better for the beginner to start with something smaller, it is equally important to start with something simpler, so this would seem to be an argument against the Poppy rig and a response to your question "what's not to like?"

    As for Poppy's sail being easy on the eye - well, I 100% agree, in fact I think that is an understatement. This is one of the more iconic and beautiful photographs in the entire JRA gallery. It's not one of those perfectly cut sails you see in the yachting magazines from time to time, but in my opinion it is absolutely stunning. Evey panel bulging and the sail pulling like a team of horses. The word which comes to mind is "windjammer".

    For right reasons or wrong, I bet this photo has created more interest in SJR than all the technical discuissions put together.

    It would be an absolute delight to see that sail on SibLim.

    Last modified: 17 Dec 2021 09:30 | Anonymous member (Administrator)
  • 16 Dec 2021 22:48
    Reply # 12197695 on 12194095
    Anonymous member (Administrator)

    Now I checked the sailplan from Slieve. There was no slingpoint indicated there, so I assumed it was at the middle of the yard. With the short mast I drew up, that resulted in a 20 deg. mast-halyard angle. By adding 75cm to the mast, that angle shrank to 15 degrees.

    This was actually why I drew up that modified SJR with a "HM-style" top section, recently. The higher-peaking yard brings the slingpoint closer to the mast.
    See diagram on posting below.


    PS: I think I use the term sling point or slingpoint the way PJR describes it, that is, the point where the halyard is attached to the yard.

    Last modified: 16 Dec 2021 23:14 | Anonymous member (Administrator)
  • 16 Dec 2021 22:19
    Reply # 12197609 on 12194095

    Thanks for coming in quickly here, Graeme, as you are so right.

    My Amiina Mk2 rig was drawn on the same sheet as the original rig, hence the dirty marks in the background. The mast is as on the original, and was not cut down. Also, I did not draw in a sling point on the yard as I guess the weight of the rig might effect the 'hang' of the rig, so the sling point is set by trial and error.

    If I remember correctly, on Poppy the junk rig mast was the same height as the original Bermudan mast, and would have been better a few inches taller as the halyard was just a little tight at full sail. I have made a note of this in the new write up, but it is a very long way from being ready, and life is full of other activities.

    Well done Graeme, 

    Cheers, Slieve.

  • 16 Dec 2021 21:24
    Reply # 12197534 on 12194095
    Anonymous member (Administrator)

    Hi Arne and Slieve

    I'm going to jump the gun here, because the power of the internet for circulating information, especially from highly respected sources such as Arne, prompts me to hope this diagram can be checked as quickly as possible.

    It looks like an exact scale copy of the Amiina Mk2 and at any rate, the corner angles of the top panel are correct as Slieve drew them. The worry I have is that the masthead halyard position is not where Edward has it on Amiina, and I don't think Slieve actually drew a halyard on the original drawing, though he did show a very tall mast and indicated a halyard position, much, much higher than shown in Arne's drawing, which I believe might have been Amiina's original mast and possibly a little higher than necessary - which I believe would work extremely well. If I am right about that, it means that means neither Slieve nor Edward will have encountered the problem I did.

    The masthead halyard point (I mean, where the halyard intersects the masthead) on that drawing of Arne's is about where I had it on my first SJR for Serendipity. And it didn't work very well. The spanned parrel/downhaul system was inadequate to cope with the geometry of that arrangement, when the sail was fully hoisted (it was fine with one reef in). That point as shown in Arne's drawing is a bit too low, in my opinion, for that sail.

    It is about where one would intuitively expect it to go, and I am guessing, Arne, that the halyard was drawn in arbitrarily by you at the time you made the Master drawing for Slieve. But I want to bring it to the attention of you and Slieve before too many people have seen it and made copies, because I think there is a chance you are going to find the mast/halyard angle is too great for that sail to drape as it should, with spanned parrel-downhauls alone. At the best, as I know, it will be very, very marginal. Most people are not going to be in the fortunate position as I was, being able to just bump my mast up a bit.

    I believe David T has made the same mistake on his proposed Poppy rig for SibLim and I reckon the same mistake was made on Fanshi and Annie is not going to appreciate my sticking my nose in, but the reported problem with that sail is exactly what I encountered with Serendipity and mast height is likely to be a contributing factor, though I have no doubt in Fanshi's case there will be other ways of correcting the problem, so it is not such a problem for her, but it would be for anyone with a SJR who wants to minimise rigging forces and use Slieve's parrel system.

    Jami will have the correct information now, but many others watching this thread will have only Arne's drawing, and will make copies of it, so I am appealing to Arne and Slieve to check it quickly in case there is a detail which has been overlooked.

    Apologies if I am wrong - but I don't think I am.

    That's Slieve's original - It probably doesn't need to be quite as high as that - that is "de lux".

    The higher the better, anyway, what Arne and David have drawn is too low.

    Edit: I might have been a bit wrong in my terminology when I refered to "sling point" - I was not referring to the sling point on the yard, which indeed has to be found by trial and error. I was referring to the point from which the whole bundle is slung - the mast height, if you like - the point where the halyard reaches the mast head. I have tried to edit the above, accordingly.)

    Last modified: 17 Dec 2021 23:24 | Anonymous member (Administrator)
  • 16 Dec 2021 20:47
    Reply # 12197478 on 12194095

    Jami, check your latest e-mail.

    Cheers, Slieve.

    Last modified: 16 Dec 2021 20:48 | Anonymous member
  • 16 Dec 2021 20:19
    Reply # 12197425 on 12194095
    Anonymous member (Administrator)

    Hi Jami.
    A couple of years ago Slieve gave me a sketch and numbers which I used in my QCAD program to produce the sail below. I am not sure if that is the final version. Hopefully Slieve will comment on it.


    Last modified: 16 Dec 2021 22:51 | Anonymous member (Administrator)
  • 16 Dec 2021 19:35
    Reply # 12197353 on 12194095

    Sorry for a slightly off-topic question, but where can one find detailed measurements (especially the top panel angles) of the Amiina mk II sail?

    (And thanks for the very interesting thread.)

  • 16 Dec 2021 09:46
    Reply # 12196264 on 12194095

    It might be useful to think in terms of there being three general areas of things to think about, in SJR design and building:

    1. Planform
    2. Size
    3. 3D design of the panels - shaping, cutting, sewing

    I shan't be saying anything much about 3., as I have no hands-on experience of actually doing it. Armchair sailmaking is not the same as real sailmaking. This, I think, is where some SJR sails have disappointed their builders. The jib-and-main combination is a much harder thing to get right than a contiguous JR sail, and anyone attempting a SJR build for the first time would be well advised to follow Slieve's instructions very closely. Experience gained on a first build might well suggest improvements to be tried on subsequent efforts, but only after taking that first build to sea.

    2. Size matters. Loads in a 50sqm sail are not trivial, whatever the design, whereas with a 20sqm sail on a 20ft boat one can afford to take liberties. 

    1. Planform is where experience gained with contiguous JR sails remains valid, I think, when applied to SJR.

    We can say with some certainty that there should be a number of parallelogram panels at the bottom. How many, and their proportions is going to vary, depending on the size and type of boat. Whereas a dinghy can use three or four sheeted battens, and a boat of the size of Amiina or Weaverbird can use five, it's my belief that six should be the norm on larger vessels, for acceptable reefing steps. SJR doesn't change that. I used seven sheeted battens on Weaverbird's wing sail, to reduce the height of each panel and make it easier to get the luff to stand bold and round, but that doesn't apply with SJR. Six sheeted battens, with upper and lower sheets on two groups of three, will give good control over twist for good performance, and control when deeply reefed, and I see no reason to need more, even with a big rig. I don't think it wise to use fewer, though, on a serious offshore cruiser.

    Above those parallelograms, that's where I would have misgivings about simply making Amiina II larger. That's where I would prefer to see less of a change of leech angle at the upper battens, for less batten loading. I like to see a right angle at the peak of the sail, so that the threadlines in the cloth can follow both the leech of the top panel and the yard. And these factors are there, in Poppy's planform. I think that's important, in a big sail, even if the balance and "drape" of the SJR reduce the loadings, relative to a high-peaked H/M sail. And the shape is easy on the eye as well as being easy on the battens and sailcloth. What's not to like? OK, Amiina II is easier to understand and will be quicker to draw out on the sail loft floor, for a first time sailmaker, but should a first time sailmaker be attempting a 50 sqm sail? I think not. 

    Last modified: 16 Dec 2021 11:37 | Anonymous member
  • 16 Dec 2021 07:32
    Reply # 12196145 on 12194095
    Anonymous wrote:

    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.

    That was also what attracted me to the design. The simplicity. The simplicity and the balance. By balance I do not mean the higher than usual 33% balance but rather the way the sail tends to keep its shape without being forced into it. Aside from being much simpler, my feeling would be that it is also less stressful to the rig. Any tinkering should start from the same beginnings... and will likely end at a very similar outcome. Adding or subtracting a panel is likely ok. Playing with the sail head very much would take more thought as that affects how the sail balances or hangs and what is required to force it into position.
  • 15 Dec 2021 23:38
    Reply # 12195547 on 12194095
    Anonymous member (Administrator)

    I would like to reinforce a request that Slieve has made. If a sail is designed which is a modified version of an existing design, it should named as a xxx-type sail, or better still given its own name. This is only fair to the designer and I think it has now been explained pretty well why a similar (but not identical) copy might well perform differently - hopefully better - but in any case, it is a new design. The catamaran sail, Fly's fore sail and Wayward's mainsail are cases in point, and there are others. They have not been given names other than the boat name as I have just done,  so not a problem.

    Lets leave "SJR" (Split Junk Rig) as the accepted universaL concept term (I don't like it much, but Slieve coined it, and it has stuck). Variant designs should not be attributed to the creator of an original design in the naming (though acknowledgement may well be declared in a write-up or explanatory notes and probably ought to be). That's a fairly well accepted protocol in other areas.

    That provides a quick answer to Marcus's question too. An "Amiina Mk2" sail is a direct scale copy of the sail of that name which Slieve designed. "Weaverbird wing sail", and "Johanna sail" etc etc should be equally unamibiguous.

    Last modified: 16 Dec 2021 00:02 | Anonymous member (Administrator)
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