Split or unsplit, that is the question

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  • 24 Mar 2024 23:09
    Reply # 13334066 on 8217505
    Anonymous member (Administrator)

    I am just as biased as you are, Slieve, and probably worse than most in this respect.
    However, like you, I don’t think of my rigs as racing rigs. In that case, I would have had to reduce sail area; because big sail area gets a harder handicap penalty than that area pays back in speed. For this reason, the Contessa 26 will win over Folkboats on handicap even if they are slower.
    I am aiming for cruising machines  -  maximum sailed miles (or sailing fun) with minimum cost and effort  -  read home-made, simple, cambered-panel junk sails with ample area.

    Frankly I haven’t done any serious cutting and trying work since Johanna in 2003. Nowadays I only do fjord pottering and fiddle with details like sheetlets, fan-up preventers and the like.

    Right now I am struggling with finishing two more strings of Johanna-style master sailplans.
    These will only differ from the first string by having the yard angle at 65 and 60°. Together with the present string of Johanna-style master sailplans (renamed Johanna 70 sails), these junk sails will now allow one to rig with mast balance between 12 and 26%.
    Seriously boring work for sure, so hope to finish before spring breaks loose and the sailing starts.

    On this very Good Friday I will be rounding 70, Odin (or whoever) willing, so getting in some sailing is a must. One never knows.


    PS: This summer it will be 30 years since I first set sail in my Malena with her home-made cambered panel junkrig. I notice that many still prefer to drift around under their flat sails...

    Malena, 19940717

    Last modified: 25 Mar 2024 15:02 | Anonymous member (Administrator)
  • 21 Mar 2024 13:42
    Reply # 13332691 on 8217505

    I do wonder whether the split rigs are really acting like a single sail that happens to have a gap where the mast is.  Rather than a jib / leading edge flap. 
    Which it is will affect the design.   If it is just a gap, then a line from the front part should run smoothly into the rear. 

  • 19 Mar 2024 22:57
    Reply # 13331946 on 8217505

    Oh Dear, I don’t want to get involved, but - - -

    There is a lot of misunderstanding about slats and flaps and other high lift devices which are used on aircraft, but have no real equivalent in the sailing world. The wing of an aeroplane and the rig of a boat are both airfoils and to work best both require a high lift/drag ratio (and here we are talking about windward sailing).

    Slats were originally developed by Handley Page just after the first world war as a method of delaying the stall and allowing the wing to operate at higher than normal alpha. This also increased the drag, but did allow a lower landing speed and therefore a shorter landing run. A similar effect can be gained from using vortex generators to re-energize  the air and encourage it to remain attached to the upper surface of the wing at higher alpha, but again with increased drag. Despite the many years of sail development I cannot think of any reports on slats being found useful on sailing boats. There is no connection between slats and the SJR.

    One of my greatest regrets is that I didn’t arrange for Arne to have a sail on Poppy with me. I was fortunate enough to sail Johanna on two occasions, which proved to be the best junk rig I had experienced to that time with a performance on par with the Bermudian rig. Despite this I still wanted to experiment with some ideas which I has reported in the article ‘Some Thoughts (on the junk rig)’. The result was the Poppy rig which at the first attempt seemed to have some advantages over the results I expected.

    As to which rig is better, well that depends on what you are looking for. Regarding performance, Arne is right in saying that until properly organised match racing is undertaken then we will never know. But pure speed is not necessarily the only answer. I keep hearing that the SJR is considered to be a racing rig which is completely wrong. I simply used the Round the Island Race as a testing ground to compare the rig against mainly cruising boats known to be trying to go in the same direction, and here I found the SJR to be equal to or better than the Bermudian equivalent boats. Certainly it is easier to sail, and therefore probably safer. (Winning the Island race requires more local racing knowledge than I had). As with the PBO articles on Amiina and Whisper, it is unreasonable to compare a home made cruising rig with a highly developed and expensively equipped serious racing boat and expect sensible results.

    As to my opinion as to which rig is best, Arne’s rig or mine, is obvious. I am totally biased, and would expect Arne to also be biased. I feel that the SJR has an advantage due to lower drag, possibly due to lower induced drag with the tip vortex pushed higher by the lower yard angle and tip of yard being further aft, but there is no way I can prove that. I did want the higher balance for better downwind balance and lighter sheet loads and that does seem to have worked. The rig drives with little heeling which suggests a good L/D ratio, but until matched raced these statements are only a ‘feeling’. Because the SJR is close to being a square rig then the loads are about the lightest possible which is rather nice.

    Graeme is right in that the SJR is not really anyway more tolerant to sloppy helming. All rigs will slow down if the rig is stalled, and with the SJR it is particularly noticeable. This suggests to me that when it is ‘in the groove’ it is particularly powerful. I feel it would work well with wind vane steering, but I never experienced that.

    After a life time of sailing all types and sizes of fore and aft rigged boats the SJR was my favorite and the only one I wanted to sail under at the end, but as I say, I’m totally biased.

    Cheers, Slieve.

    Last modified: 20 Mar 2024 18:04 | Anonymous member
  • 19 Mar 2024 11:00
    Reply # 13331472 on 8217505
    Anonymous member (Administrator)

    For what my opinion is worth, probably not much, I think Len is not quite correct in saying "So it turns out the split part of the sail is used in the same way as on a plane, for slow wind speeds."  Quite frankly, I don't think the split itself does anything much at all.

    My understanding of the SJR is that it allows the sail maker to build the best possible foil shape into the forward 30-35% of the chord which is the most important part of the sail in regard to lift, and to maintain that foil shape unimpeded on either tack. "Best possible foil shape" also includes an entry which is quite blunt, so it is possibly worth the extra little bit of work in building the jibs using angle shelf foot in order to get that perfect shape right up near the luff, because the jib panels will be unimpeded by the mast. The purpose is to improve the ability to sail to windward (which is not necessarily the the same thing as merely being able to point higher). Whether this objective is actually achieved (better windward ability compared to a cambered contiguous sail) is still open to rigorous testing. All I can say is that my SJR goes well to windward - that is the result also of a good hull shape, and good harmony between the design of the sail and the design of the hull. It is possible the boat would go just as well to windward with a well proportioned cambered contiguous sail - I don't really know for sure, but consider it quite likely.

    With all due respect to Paul McK (and I really mean that) - I don't think discussion about slats and slots has much relevance to junk sails. A fixed leading-edge device on an aircraft wing which utilises a gap between the device and the main part of the wing is usually referred to as a "slot". If the device is retractable, it is usually referred to as a "slat". The purpose of either is the same - to allow a very high angle of attack which would otherwise put the wing into a stalled condition. Landing, taking off, flying at a relatively low airspeed or "on the back of the power curve", steep turns -  all may involve high angles of attack and one or both wings being closer than normal to a stalled condition. Slats or slots may be useful then, if you want the aircraft to keep flying. I am not sure if sailing to windward is in any way analagous to an aircraft wing flying at an unusually high angle of attack, as in a slow-speed short-runway landing or take-off.

    I also don't think there is much relevance to the SJR in the long-held notion about "the slot effect" which is supposed to arise from a genoa sheeted in correctly on a bermudan sloop. I think this is what initially attracts people to the SJR - the bermudan paradigm - it did for me at first anyway. But I doubt it now, and the sheeting angle of a SJR jib panel, relative to its corresponding main panel, is built into the sail and not adjustable anyway.

    It is possible that there is a bit of a "slot effect" at times on a SJR - I do not know, but I doubt if the effect is much, if any. And it may be that if the SJR sail is offered to the wind at a very high angle of attack, that the slot might come into effect and the stall may be delayed - but why would you want to do that anyway?

    [Answer - you might be doing that on a broad reach and close to running before the wind - I have always felt that my SJR is superb down wind  - I never thought of that before. When running and letting the sail go out beyond 90 degrees, the sudden effect of the SJR sail becoming unstalled is remarkable - a sudden lurching heel to windward which once nearly had me overboard ... maybe there is something in that]

    The question "split or unsplit?" is actually a bad question, as it focuses the mind on what is the least relevant thing about a SJR - the split itself. I can say that bluntly without (for once!) offending anybody, because I think it was me who framed the question at the beginning of this thread. With hindsight, I think now that it is not a useful question, although it has led to some very interesting comments.

    Another thing, and it has been discussed on this thread, the SJR is supposed, in theory, because of the entry shape of the SJR jibs, to give the sail a high "alpha tolerance", that is to say, the angle of attack can vary quite a lot without affecting the windward performance - or to put it another way, the sail should be fairly tolerant of sloppy helmsmanship and still perform well to windward. I doubt if that is actually the case, although it might be just something about my sail, but I have found that careful helming is quite critical with this sail, and if I get a little sloppy on the helm (which often happens, as I am not much of a helmsman) the performance goes from "very good", quite quickly to just "very ordinary" so I am inclined to think that while the windward performance is very good, the alpha tolerance on a split sail is not necessarily all that great. This is consistent with the results of testing that was done some time ago, when it was found that the soft wingsail had very high alpha tolerance but the SJR, while being very good, did not have as high an alpha tolerance as the wing sail. I don't know if that constitutes a proof, but anyway, it leaves that element of performance also at least open to question and further testing.

    There are some very interesting points raised in this thread, by others, in regard to attachment of air flow to the surface of the sail - which I found quite interesting and worth a second read. Particularly the comments made by Len, Slieve and Arne in that regard. But I don't know if "split or unsplit" has much to do with those things. In theory it should, at high angles of attack, but in practice? And if so, is that useful when sailing to windward?

    Personally, I like the SJR very much (at least, the Amiina Mk 2 version which is the only one I know) for a number of other reasons, mainly due to the high mast balance which the SJR allows. I have an aversion to the antics of a single sail (cat rig) boat when on a broad reach or running, with all the sail out one side - the high balance of the split rig mitigates this to some extent. It also reduces the sheeting forces required - in fact all the forces on the sail which are required to hold it in shape, seem to be less required. A bit of vertical tweaking on the parrel-downhauls is all it seems to need to set well- no hong kong parrels, throat parrels luff hauling parrels etc needed. I like to kid myself that the jibs and the mains both have optimal foil shapes on either tack, never crushed by the mast, but that may be more of an aesthetic advantage and it is quite possible there is no real performance advantage from that. I don't know. The rig inflates and accelerates very quickly between tacks, making the boat very handy when tacking up a confined waterway. Is it better than a contiguous sail in that respect? I don't know. There are other little things too, which might be just imagination driven by personal preference.

    So, if you like a high balance sail, then SJR is certainly an advantage. (But probably a waste of time unless the balance really is high, like, around 33%)  If other matters dictate having the mast placed a little further aft in the hull, then, again, the high balance of the SJR allows this and SJR then has an advantage. All things considered, I suppose the further back from the bow the better, for a single mast junk - but often there is not much choice in the matter.

    These are not huge advantages. There are a few small downsides too. The Amiina rig with its high mast balance and correspondingly low yard angle gives what I believe is probably a better plan form from the point of view of drag - (advocates of the high peaked yard and greater apparent luff height might disagree) - Slieve refers to vortex shedding, but I'm a bit out of my depth at that point so i won't labour it. But the down side is that because of the plan form, a slightly taller mast is required by the SJR in order to carry the same sail area at the same aspect ratio, as compared to a high peaked, lower balance sail like the Johanna sail. On the same mast height, but with a slightly reduced sail area, would the Amiina rig match a Johanna sail, to windward? I'd like to think it would, but who knows? I suspect that the SJR "punches a little above its weight" and that the difference probably would not be much anyway, either way. There is probably a bit more work in making a SJR compared with a making a contiguous sail - but if you are an amateur making your own sail, what of it? Making a sail is an enjoyable task. There's no harm in a bit of extra sewing practice, and it could be argued that you are handling smaller panels. And there is probably little extra time required to loft that brutally simple (but deceptively well-proportioned) Amiina sail, with its replication of panels.

    I would like to reach back into an earlier post on this thread, and give the last word on this post to Slieve - especially his last sentence: "Only by building two rigs and fitting to identical hulls and sailing them together would we find the answer. Even then we would still have to evaluate the different physical characteristics.

    Until we do that then we will always be asking the question, to split or not to split. Perhaps we should concentrate more on mast position or ease of handling when selecting a rig".

    Last modified: 28 Mar 2024 23:15 | Anonymous member (Administrator)
  • 19 Mar 2024 07:26
    Reply # 13331448 on 13331187
    Anonymous wrote:

    What I tried to express was that I don’t think that a two- or multi-sail rig  (like the SJR, Aero Junk or Bermudan sloop or cutter), will point any better than a boat with a good, single  contiguous junk sail or a good dipping lug.

    The leading edge slats on aeroplanes are used for taking off, landing or making sharp turns, not to improve speed or range during cruising.


    Aye, leading edge slats are for taking off and landing. That is to extend the speed range the wing will fly at without stalling. When the wind speed is high, the lift does not matter as much because the lift is more than needed to move the vessel as fast as it can go anyway and so the sail is reefed. By the time we get to air plane cruising speeds the sail is reefed to handkerchief size (the last two panels which tend to be one piece and not split). It is the slower wind speeds where the sail is set to full size.... kind of like landing and taking off in a plane. Sail boats are slow, the wind speeds we are most interested in are likewise slow. So it turns out the split part of the sail is used in the same way as on a plane, for slow wind speeds.

    Does this prove any points? probably not, comparing the slats on something trying to slow down enough from 50 to 100 times (100 times on my boat anyway) the speed of a sail boat to only 10 times the speed of a sail boat (and still double the wind speed of what can be called a hurricane) to avoid a runway excursion, might have some pitfalls. Split sail powered boats have been raced and done reasonably well, considering that the rules really don't know what to do with them. I have heard less of single panel sails in any kind of race.... but then I don't follow the racing scene that close.

    So I guess the idea there needs to be some more rigid comparison done makes sense. I think for a lot of people it has more to do with finding the right place to put the mast.

  • 18 Mar 2024 18:32
    Reply # 13331187 on 8217505
    Anonymous member (Administrator)

    What I tried to express was that I don’t think that a two- or multi-sail rig  (like the SJR, Aero Junk or Bermudan sloop or cutter), will point any better than a boat with a good, single  contiguous junk sail or a good dipping lug.

    The leading edge slats on aeroplanes are used for taking off, landing or making sharp turns, not to improve speed or range during cruising.


  • 18 Mar 2024 17:30
    Reply # 13331146 on 8217505

    Arne, what am I missing here? In this post you are making a case for optimising the L/D ratio and in the thread on Draft in the Junk Sail here you are making a case for not fretting over the L/D ratio as it can't be much improved on (4:1 compared to higher ratios in aircraft). Are you differentiating between lift induced drag and windage drag or something?

  • 18 Mar 2024 13:37
    Reply # 13330986 on 8217505
    Anonymous member (Administrator)

    Leading edge slats

    In JRA Magazine 94 (March 2024), Paul McKay draws a link between the slotted junks (SJR or Aerojunk), and aeroplane wings with leading edge slats.

    As an example of the latter, the WW2 liaison plane Fieseler Storch is mentioned.
    Yes, those leading edge slats worked (and still work) well at increasing lift as it allowed the pilot to fly at a much higher angle of attack at take-off and landing (read; shorter runway needed). I have read about this plane. The company planned to improve their plane by making the slats retractable. This was to reduce drag at cruising speeds. However, the war prevented this.

    Here is my point: Although a well made foresail-mainsail split may give an increased maximum lift, this will happen because of higher angle of attack and thus increased induced drag (drag dues to lift), just as on that Storch.

    I am therefore sceptical to SJR and Aerojunk sails with respect to performance to windward, where optimising the lift/drag ratio is the name of the game. Until proper match-racing proves me wrong, I don’t think that the sails with splits are any faster to windward than a well made one-piece, cambered panel sail. However, it could be that the 2-piece sails are faster in a round-the-cans race. Only match-racing will confirm this or that.

    On the other hand, the high-balance split sails have proved to have lighter sheet loads and easier steering downwind, but that is another story.


    Last modified: 18 Mar 2024 13:38 | Anonymous member (Administrator)
  • 15 Jun 2020 08:50
    Reply # 9037642 on 8217505

    You'll need to go back to NL no. 26 to get the story of Upik's passage from the Canary Isles to Cape Town - and it's a story that really does illustrate what happens to a "fragile" rig on an ocean passage. Undersized mast with holes drilled in it at crucial places, sails with UV-weakened seams, masthead blocks falling apart ...

    It is interesting that Tystie made the same passage in 2006, with the addition of a stop at Fernando da Noronha (NL no. 48 pp20-21). Just like Upik, we got an anchor jammed in the boulders at Isla Trindade while trying to do some repairs (in our case, only sealing off some deck leaks). Like Upik, we had a rough passage south of Isla Trindade, getting knocked down twice, but there were no rig failures, only minor damage to the pramhood. "Robust" enough.

  • 15 Jun 2020 06:49
    Reply # 9037564 on 8217505

    That certainly is a "Junk" sail. More of a windcatcher, really.

    Now I must read the article, to get the story behind the picture.

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