SJR - A wider discussion on future possibilities

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  • 28 Dec 2021 08:19
    Reply # 12219220 on 12194095

    Graeme: "And do not go much below 33% or there is no point in SJR , but that's just my opinion".

    Indeed - my Galion 22 SJR (as discussed on my conversion thread) might be a living example of this. Basically I am very satisfied, but the lack of jib power is evident, at least this is what i feel. Might be some other thing, of course.

    (Anyone interested in trying themselves and buying the sail? I would prefer - but can't afford the cloth - making a new sail rather than start playing with extending the battens for longer jib chord. I bet the mains would also make a nice, very high-AR sail without the jibs...)

    Last modified: 28 Dec 2021 18:37 | Anonymous member
  • 28 Dec 2021 01:12
    Reply # 12218662 on 12194095
    Anonymous member (Administrator)

    Balance, yard-angle, halyard angle and mast height (all related), and size or number of panels, seem to have run their course as subjects for discussion.

    Top panel shape, as introduced by Arne in the "lateral thinking" thread - and the discussion about Amiina Mk1's top panel, or removal of it, could possibly be carried on here.

    Vortex drag

    While we are in a talkative Christmas mood, I wonder if anyone has a comment on the topic of top panel shape in regard to aerodynamics. Slieve has written: "I've settled at no more than 30 deg slope to the horizontal [yard angle], and if totally honest I would make the yard longer than the battens! Aesthetics stop me doing this. The key to minimising induced or vortex drag is to push the vortex as high and as far back as possible...  ...Forgetting aesthetics and going for efficiency I would draw the luff and the leech parallel and vertical all the way from bottom batten to the yard, extending the yard length over the batten length to match. With this I believe the best yard angle would be between 25 and 30 deg."

    (Take a look at both the boats in this picture)

    Clearly there is more to consider than the aerodynamics of vortex drag, since Arne's Johanna-style high peaked yard has its own advantages (effectively a longer luff, among other things including extra area or shorter mast) and for all we know, performs at least as well. Probably not much point in debating that (I do still prefer low yard angle, for other reasons, but would love to see Arne's SJR/Hasler-McLead hybrid given a trial).

    Here's a question on the subject of reducing vortex drag (I'm way out of my field here). Aircraft these days sometimes have winglets, for a similar purpose, I believe. Winglets (wing tip appendages) look to me like endplates on rudders (but that could be a crude misunderstanding on my part). Is there a connection? Could an end-plate at the yard reduce vortex drag?

    I was wondering if would it help if the yard were made from a wide tee-section, at least on the aft part, acting as an "end plate" (or winglet, if indeed they are the same thing) ? I am talking here about a fairly low yard angle sail.  And on this thread, of course, particularly in regard to SJR, but not exclusively.

    Last modified: 28 Dec 2021 02:21 | Anonymous member (Administrator)
  • 20 Dec 2021 20:32
    Reply # 12207010 on 12194095
    Anonymous member (Administrator)

    Thanks Maxime

    I have a feeling you are probably correct in the first point you make, in regard to halyard and other control line forces - if only because when  it all boils down,  this is the angle of the halyard force vector (when all the other forces are in play it may vary slightly from what is shown on the plan). However, the CoE offset demonstrated by Arne does help one to form an understanding of what is going on, and is particularly illuminating in regard to sheeting forces - and the heavy helm which tends to develop with most cat rigs going down wind (of which, Amiina 2 or any highly mast-balanced rig will likely be among the best behaved).

    Your second point concerns me a bit, and here is why: what you wrote is perfectly correct (in the static situation). Below: same outline, different moment of force about the mast.

    But you are attempting to explain the (static) balance forces, whereas explanation is not the purpose of the definition. The purpose is of the definition is purely to be unambiguous in the design of a SJR sail, so that lofting mistakes are avoided. The slot won't vary much - it is specified, perhaps a little arbitrarily, as being equal to the diameter of the mast, and I would regard it as a constant, not a variable.

    Within the bounds of what is reasonable and likely, I think the definition we have been using, is appropriate and can be made to unify (sort of) with the standard definition of mast balance for contiguous sails, and allow (sort of) apples-with-apples comparisons.

    A definition can be quite quite arbitrary, and it does not matter what it is, provided everyone understands and uses the same definition when bandying numbers around.

    The definition I gave (and Arne used) for mast balance - the proportion of a lower batten which is ahead of the mast centre line - is in accordance with what Slieve intended when he described his SJR sail as having, say, 33% "balance". This high mast balance is thought to be close to the limit of what will work safely, and anyone fooling around with different definitions of their own will create ambiguity and might risk failure in the making of a SJR. You can call it what you like, and leave out the word "balance" altogether if you prefer, but this is the rule to use when lofting a McGalliard SJR sail: Keep the slot width about equal to mast diameter, and do not go much above 33% of the sail outline ahead of the mast centre line - unless you want to be a pioneer. There is reason to believe 35% may be possible.

    Measuring along the length of a lower batten is near enough and good enough, and less likely to lead to error.

    (And do not go much below 33% or there is no point in SJR , but that's just my opinion).

    [If you start analysing width of slot, area of jibs etc etc someone is going to get it wrong, and over-balance, and then others come along and blame the rig for the failure (or blame the very principle of higher than normal balance, as happened before). Call it a rule of thumb, if you prefer. At this early stage in the development of the rig, perhaps one can be forgiven for being a bit "touchy" about it. Remember, this "definition" is for amateurs (like me) not for aerodynamicists.]

    Arne wrote: Hasler and McLeod mention the option of having downhaul spans. These are meant to help reefing when sailing downwind (without needing to round up first).

    To avoid confusion here, the spanned parrel-downhauls used on a SJR (here and here) may not be of much assistance in lowering the sail when reefing down wind. I've never had to try (I mean, never needed  their assistance for that), so I don't know. I suppose they would help?

    Above: two forms of a spanned parrel-downhaul pair. (McGalliard). Serendipity has a third variation, which I prefer.

    I must point out, anyway, that reefing downwind is easy with spanned parrel downhauls because as soon as the halyard is released they go slack, allowing battens to fall down easily. If down-wind pressure on the panels were to make it impossible to lower the sail, then you might have to round up, because pulling on the parrel-downhauls and tightening them doesn't actually give you a direct downward pull.  I just don't know, can anyone help?. If a conventional set of control lines is used together with a set of downhauls which are solely downhauls - that is maybe what Arne is talking about - then you perhaps get the best of all worlds, but what I have been trying to suggest all along is: this would mean an awful lot of control lines which, with SJR anyway, would all need to be adjusted at every reefing event.

    Arne - it seems to me you have opened up a new development pathway for SJR which is worth trialling. I am very tempted to pull the top triangle off Serendipity's sail and give it a new (longer) yard and new upper section, like your HM style, just to see what happens - with a view to examining the control lines necessary, rather than performance. Next winter maybe. Thanks for your creative input Arne.

    Here are four more non-McGalliard SJR variants: 

    The catamaran sail is a crude Amiina look-alike, with six lower panels. Its not my cup of tea, but David likes the look of it. The ketch scow (Wayward) has a split mainsail - interestingly in this photo the mains panels comprise centre panels only, the shelfs have not yet been made and the camber is achieved by differing-length temporary "Thai lashings". (Its a "shelf-foot" sail with the shelfs missing). It has five lower panels. The single upper panel is a polynesian crabclaw (negative roach). I believe Dave Z is very happy with it. The schooner (Fly) has a heavily forward raked foremast carrying a 32 sq m split sail to the owner's design, with two upper panels, five lowers, and a rather shortish yard. The sloop (Hihi) appears to be an unraked (vertical mast) version of Fly's fore sail, with one less lower panel. It would be interesting to know the sheeting and control lines used on these rigs, and what their owners have to say about their performance.

    For now, I still prefer the Amina mk2 sail. And I do think the raked Poppy sail would look lovely on a SibLim 10m, if it could be made to work without too many control lines (which, I have my doubts. David - what about just setting the mast plumb?).

    Here is a familiar photo of Amiina, slicing through a short chop and smoking along under her old Mk 1 sail

    Thanks those who chimed in. I was hoping a lot of people would add to this thread, with descriptions of their own hands-on experiences of SJR . Please do.

    Currently the discussion seems to have settled on panel size (and number), control lines- and upper sections, as introduced by Arne.

    There is a lot more to be discussed in the New Year.

    I hope everyone following this thread will have a safe and happy Christmas.

    Last modified: 21 Dec 2021 06:17 | Anonymous member (Administrator)
  • 20 Dec 2021 15:57
    Reply # 12206312 on 12194095


    This has been an interesting thread to follow. I have no insights of the practical kind, but here are some technical thoughts that sprang up as I read your messages:

    1) Halyard to vertical angle. There were suggestions that this angle was a proxy measurement only, and that what matters is the angle between vertical and a line drawn between the sail's center of gravity and the halyard crane. I disagree. In my view, the halyard to vertical angle is the correct measurement for understanding the force diagram, and the fore-aft force we have to compensate with other lines. The CG-to-halyardcrane-to-vertical  angle (let's call it CG-to-vertical) in fact already accounts for the compensating forces, as it would not be where it is if the other compensating lines were not in place, along with the halyard. CG-to-vertical would be zero if other compensating forces (besides the halyard) were not already applied. Thus, the halyard to vertical is the correct angle to use for understanding the force-aft force being generated by the halyard, in isolation.

    2) Definition of balance. Maybe I missed some finer points, but I didn't find the proposed definitions satisfactory. Batten length balance, and sail area balance neither really do the trick, as one could have (for a silly example) 10% of the sail area several meters away across a huge split with long battens. I think the best approximation of true balance we could get, absent aerodynamic forces, is by comparing the moment of the sail area forward of the mast, with the moment of sail area aft of the mast. Moment being respective centers of area, forward and aft of the mast, multiplied by distance (from the mast).

    Best regards and merry Christmas to all.

  • 20 Dec 2021 09:42
    Reply # 12205384 on 12194095
    Anonymous member (Administrator)

    To drape or not to drape...

    I don’t want to draw any firm conclusion about the need for control lines on the HM-style SJRs. After all, these sails are only armchair ideas, so far.

    However, if I were to rig such a sail, I would start with making the top section set well.

    • ·         I would give batten one from top  an ordinary batten parrel, short enough to prevent the sail from moving forward of the working position on the sail plan.
    • ·         I would fit an ordinary YHP to counter the forces from the sheet.
    • ·         There is probably no need for a THP or any other running or standing parrels near the throat end of the yard. The very short luffs of the top panels have proved to prevent the battens from moving forward or aft (at least in my HM style sails).
    • ·         Further down I am sure Slieve’s combined batten parrels and downhaul spans will do the job.

    Hasler and McLeod mention the option of having downhaul spans. These are meant to help reefing when sailing downwind (without needing to round up first). Since I only sail inshore, I have had no need for these. If the sail is a bit reluctant to come down, a light tug on the THP is enough to bring it down. However, for offshore use, downhauls could be useful. I think Slieve’s version could work fine on ordinary one-piece HM sails. When spring comes, I must remember to fit one such span to Ingeborg’s sail, just to see how it works.

    I rest my case  -  time for preparing just a little for Christmas...

    Cheers, Arne

    Graeme, seven battens need not weigh 40% more than five battens. Remember, each of them will only take roughly 5/7 of the load, so may be built lighter.

    Last modified: 20 Dec 2021 10:35 | Anonymous member (Administrator)
  • 20 Dec 2021 00:19
    Reply # 12204434 on 12194095
    Anonymous member (Administrator)

    A parrel system for Arne’s hybrid.

    If we can get the non-parallel top panel(s) to act as a headboard for the lower sail, then the rest of the drape is achieved by gravity alone. This is an over-simplification of what happens in reality, but it’s a good paradigm to begin with.

    The Amiina2 sail is weak in this respect, because the sail cloth alone can not stop the next batten down from the yard from slumping forward of the yard. (Just saying – in practice the Amiina2 sail can be made to drape just fine in practice – that’s one of its strengths in fact. As Arne says, though, this does require a sufficiently tall mast).

    The HM/Amiina hybrid that Arne has drawn tempts me to suggest a loose attachment of the yard and top two battens all together, at the throat (the foremost part of the yard). The top “triangle”, with a single standing parrel, could then perhaps be made to actually act as a large headboard. (I think Dave Wayward might have done this, and for me, the concept came from Dave's website). Would that affect the stacking and stowing away when the sail is fully lowered?

    I don’t have any successful experience with standing parrels up there (I did try one) so I can only ask for comment, I can’t say it would work. A standing parrel for the throat seems an ugly option to me, and might be troublesome to haul up and set? A short standing mast parrel on the 1st or 2nd batten below the yard would, of course, need to be slack enough to allow for mast taper, and might also be difficult to lower, I do not know. Perhaps parrel beads would help. I expect Arne or anyone else familiar with all the parrel options will know what I am talking about, and will have a better idea than me about what will or will not work. Arne's clever proportioning of the sail means, I think, that the horizontal forces up there should not be too great, though they will be greater than Amiina 2 (see PS below).

    After that, Slieve’s spanned running parrel downhauls ought to do the job. This gives two or possibly three pieces of running rigging to tweak whenever the sail is reefed or shaken out.

    (Remember too, there must be enough room below the boom to allow for the span of the spanned parrel downhauls. Half a panel width, plus a bit more - another possible advantage of Arne's hybrid, given that his panel widths are less.)

    Another question, to those of you out there who have SJR – especially in some non-McGalliard form. Do the panels of a SJR all need to have a running downhaul? I think they do, but I have never been able to try without, except on the boom, which eventually I felt needed to have a downhaul too, and I gave it a standing one.

    The point of these questions is to try to ascertain whether or not the HM/Amiina hybrid can get by with no more running lines than 2 or at the most 3 (Apart from the sheets and the halyard of course) and whether or not running downhauls would have to be part of the package.

    PS the tendency of the sail to swing forward and need further restraining parrels can be measured roughly, from these diagrams. HM/SAmiina hybrid with is short mast is slightly worse because of the slightly greater offset of its CoG - and up to 40% worse I guess, because it carries the weight of 7 battens below the yard, instead of 5. So,  the question of drape, and the amount of running rigging that will be required to achieve it, is still very much an open question.

    Well, that’s your homework for tonight.

    Last modified: 20 Dec 2021 01:22 | Anonymous member (Administrator)
  • 19 Dec 2021 01:15
    Reply # 12202274 on 12194095
    Anonymous member (Administrator)

    You don't have to remind me, Arne, I am well aware that all of this is in a second language for you, though reading your posts, one would hardly guess. Your mastery of English is outstanding and I am constantly noticing and admiring that. 

    Last modified: 19 Dec 2021 09:30 | Anonymous member (Administrator)
  • 19 Dec 2021 00:51
    Reply # 12202252 on 12194095
    Anonymous member (Administrator)

    Loaded sentences  -  that is me.

    Graeme, I have to remind you that English is not my first language. Writing English sometimes feels like playing a harp with a few strings missing.

    You wrote; (as long as it is not given too short a mast).
    Yes, that’s the point. That rig needs a tallish mast to reduce the halyard angle. My version with a 51° yard ends up with next to vertical halyard. That’s why I have made the halyard span a little shorter than usual  -  only 15% of the yard instead of 18.

    As for the one-piece JRs I sail, I feel they are easy enough to keep in the groove. Those leech  telltales are useful, though.


    (..time for the bunk...)

    Last modified: 19 Dec 2021 00:55 | Anonymous member (Administrator)
  • 19 Dec 2021 00:31
    Reply # 12202209 on 12194095
    Anonymous member (Administrator)

    I wanted to reduce the halyard angle of the Amiina SJR to make the sail hoist easily and drape nicely.

    That's a loaded sentence Arne. In fact I think you might have made a typing error. The fact of the matter is, the Amiina SJR already hoists easily and drapes nicely.  (as long as it is not given too short a mast).

    Perhaps what you mean is, you wanted to retain its good quality of draping nicely, and still be able to hoist easily, yet do so with a with a shorter mast. I think that is what you really mean - and provided it will work with a system of parrels which is simple, and also incorporates a light downhaul of each panel, then you have surely suceeded, and well done.

    To be honest, I have my doubt if a SJR does perform that much better (speedwise) than a properly made one-piece JR. Me too. I feel that it ought to perform a little better up wind, but have no idea whether it really does, or not - all I know is, it works well. A badly designed SJR could quite possibly be not as good as a contiguous sail, which is why I think your "tongue in cheek" hybrid ought to be tested on a smaller size, though on paper, with my limited knowledge,  I can see no reason why it would not be just fine.

    I feel that the Amiina2 sail is very efficient when sailing to windward, but I will say one thing, it needs careful helming. If you lose concentration it very quickly falls back to ordinary. That's what I found, anyway. I wonder if Edward has found that.? I believe this is called low "alpha tolerance"? (I'm a bit out of my depth here). I believe that in the carefully calibrated trials which have been recently carried out, the most tolerant was David's Weaverbird wingsail. That's an important factor to consider in the "which sail is best" question.

    [ I always wished that one day at a tall ships regatta, I might be able to enter Serendipity and persuade Lynda (Fantail) to take the helm. I think then, that sail might punch above its weight and surprise a few people. Anyway, for an ordinary helmsman, it probably doesn't matter what sort of sail as long as it is well cambered, well proportioned and simple and safe to operate. (And proven robust, as I can hear David say). 

    And another thing, on the day of Annie's first sailing of Fanshi I repeatedly went to the back of the fleet to do filming (here and here) and Serendipity with her little Amiina 2 sail, and 15' of waterline length, caught up with the fleet again each time easily and was overtaking Zebedee as we went into the bay. Nobody noticed I think, or nobody mentioned it anyway. Oh well - sigh - one sometimes has to blow one's own trumpet].

    edit: (..time for swinging the casseroles here, Edit  -  play with the casseroles, i.e cook dinner...)  Oh, is that all you meant - time to cook dinner - I was expecting a more colourful Norwegian colloquialism!

    Last modified: 19 Dec 2021 01:33 | Anonymous member (Administrator)
  • 18 Dec 2021 23:45
    Reply # 12202149 on 12194095
    Anonymous member (Administrator)

    Thanks Graeme,

    now I have incorporated your better phrasing into that text.

    My motive for modifying the Amiina SJR into a 7-panel version was not to make the rig faster. I just wanted those six gears and smaller top panels. Remember, I once had seven panels on Broremann’s JR of only 10sqm ( ). Never for a second did I think; “oh, I wish I had made that sail with fewer panels”. Never. In addition, I wanted to reduce the halyard angle of the Amiina SJR to make the sail hoist easily and drape nicely.

    To be honest, I have my doubt if a SJR does perform that much better (speedwise) than a properly made one-piece JR. Now that Paul Thompson has shown us that a JR can be rigged with up to 27% mast balance (so far), there is more room for adjusting the mast position to the deck layout or interior. That’s why I have started to play with lower yard angles, like on Ketil’s Kelt 8.50 ( These sails will also bring the CE closer to the mast and make sheeting and steering downwind a bit easier. Not quite as good as the Amiina-style SJR, but still.

    My recent inputs on the SJR field surely belong in the tongue-in-cheek league. I leave to anyone to follow or twist the idea, just as I twisted the Poppy and Amiina SJR idea.


    Last modified: 18 Dec 2021 23:51 | Anonymous member (Administrator)
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