The Shape In A Junk Sail

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  • 04 Jun 2025 03:40
    Reply # 13506471 on 13500036

    Jan, I would still call it a Bermudan sail, a cross-cut, full batten, square top main. I just made it with the exact same sail cloth and battens as my junk sails.

    Most Bermudan rigged boats used for racing fly a square top main sail these days because they say it helps induce twisting in the sail, reduces the tip vortex and maximizes effective sail area.

    I have not tried sheeting such a sail from the leech nor have I tried reefing although I am sure it would have worked by tying the battens together. 

    I know sailors who have spent a small fortune modifying their Bermudan rigged sloops to be rigged with a split backstay in order to make room for a square topped main. I did not make my sail the full height of my mast, so I did not have to modify anything. The sail still fit within the rigging.

    Personally, I think it's funny that these modern boats are starting to have issues with rigging getting in the way of their sails. How much longer before they decide unstayed masts are the way to go?

    - Colin Clayton

    Last modified: 04 Jun 2025 03:47 | Anonymous member
  • 01 Jun 2025 21:53
    Reply # 13505517 on 13500036

    Well said Arne.

    Your experiments with the Hasler/ Mcleod rig on a boat you already knew well were very well though out, and very well reported. While there were other interesting experiments being carried out at about that time I believe your efforts were a major step forward in the western use of the junk rig.

    It may be that the hinged battens could have been developed further, but they did not have the structural integrity not overall simplicity of the barrel cut panels. Having enjoyed sailing with you I will admit it was tempting to simply copy your well documented examples, but I came to the junk rig with a very different background and wanted to experiment with ideas based on my model and full size aeroplane experience which I wrote about in the ‘Some Thoughts’ article. This lead me to try the SJR and I’m please to say we are both very happy with our final results. I just wish I could be as enthusiastic as you when it comes to producing a write up.

    Colin, with two identical boats with identical sails but with one sail well worn and stretched are not two identical boats. Obviously to blown out sail will give inferior performance even with the telltales flying, however it will give even worse performance if stalled, so the ‘tales do have their use. As I say, they are not a design tool, but are an aid to help get the best performance out of the rig in use.

    Mauro, the Deskbreeze looks like great fun, but I doubt if it would help develop a better rig unless some type of balance was added.

    Paul, you reference to David T’s wingsail is introducing a much more sophisticated aerodynamic set-up, but it is getting away from the simple structures of the single surface rig. For ultimate performance it has great merit, but I don’t believe that is what the average junk sailor is looking for. Yes, I am suggesting pushing the vortex up and aft, and not letting it curl down the leech. The profile of the SJR is so much better than the normal cruising Bermudan mainsail with roach in this respect that I feel it must be helping the L/D ratio. I feel Poppy would have been better with a longer yard.

    Cheers, Slieve.


    Last modified: 01 Jun 2025 21:59 | Anonymous member
  • 01 Jun 2025 21:43
    Reply # 13505510 on 13500036

    Colin, your experiments are very interesting. I just wonder what I could call the mainsail on your catamaran? Is it still a junk sail? Or a simplified version of the Bermuda sail made using a method borrowed from junk rigging (joining horizontal panels)?

    I guess the choice of material is also important here, allowing for the proper trim of the sail? Either way, the idea is very interesting!

    I am also intrigued by how the reefing maneuver of this sail is performed? Have you also tried using the sheet system usually used in junk rigging?

    Keep junking(as Rael tells)

    Last modified: 02 Jun 2025 11:06 | Anonymous member
  • 01 Jun 2025 20:44
    Reply # 13505499 on 13505383
    Anonymous member (Administrator)
    Paul wrote:


    Considering a better aspect ratio (higher mast) is not a realistic way to go (though it would be the most effective), what else can be improved? There is one major issue in which the sewn-in, cambered junk rig (and the split rig, too) defers from the bm rig: the batten pockets and separate panels, which reduce the amount of "good" profile shape to about 60-70% of total sail area. Hmmm! Hinged battens with flat sail don't suffer from this, as well as David T.'s wingsail. Taking the wingsail aside, due to its other aerodynamic benefits: would a hinged batten sail work significantly better upwind than a sewn-in camber sail?



    Paul,

    I had my Albin Viggen  Malena’s sail, with both flat JR (tan), the same sail with hinges (NL #24), and finally a new (blue) sail of the same size and with cambered panels (NL #30). I don’t dare to draw too firm (or objective) conclusions  -  there were so many factors flying about  -  but here are my subjective impressions, as I remember them 30-35 years later.

    Btw. when I rigged Malena with her first JR in 1990, I had already sailed her a lot for the last nine years, so I knew her well.

    • ·         1990: Her first flat sail was a huge disappointment when it came to sailing in light winds and upwind. There were a few missed tacks  -  unheard of with the original rig.
      Malena was simply a lame duck in light winds. Had I not found a way to improve the rig, I would have scrapped the sail and refitted the Bermuda rig.
    • ·         1991: When I modified the battens with hinges to produce a symmetric 10% camber in the same sail, the boat was like transformed. Suddenly she became powerful and close-winded. In light winds I even overtook another sister boat by being more close-winded.
      Now, suddenly Malena felt over-rigged  -  the 80kg mast on a 1400kg boat, simply became too much. The remedy was to chop a metre off the mast and plane off 1-2cm of its diameter.
    • ·         1994: The first sail with 8% cambered panels, planned from the start, was built. The mast was still the shortened one, so one of the panels of the new sail was rolled up tightly on the boom, pending the arrival of a new mast.

    So how did these two sails compare?
    For brute force, the hinged batten sail may have been the strongest. However, the hinged sail had 10% camber versus 8% in the barrel-cut sail. On the other hand, the cambered panel sail had had the max-camber point positioned further forward (35% versus 50%), so the added weather helm experienced with the hinged sail, was gone. Overall, I felt that the cambered-panel sail was as fast or a little faster to windward than the hinged sail.

    Many words have been produced about the possible reduced efficiency in this sail, near the battens. However, if we look at the first and last meter of these panels (near luff and leech), one will see that the groove is almost none-existing; the air entering the sail and leaving it will meet an almost homogenous sail (consistent angle of attack and departure).

    I know, I know, these are armchair speculations from my side, so I leave it to you to look more closely into it. Until you find any hard evidence, I conclude that the cambered-panel sail is about as efficient as the hinged sail, and with much more freedom to vary the sail’s mast balance. This last point is important when planning a real JR for a real boat to sail on real water.

    Conclusion: hinged sail  -  been there, done that; thanks but no thanks...

    Cheers,
    Arne



    Last modified: 01 Jun 2025 23:02 | Anonymous member (Administrator)
  • 01 Jun 2025 20:09
    Reply # 13505488 on 13500036

    Arnie, your sail is beautiful. It looks like the upper panels have less camber than the rest. I still contend that if the bottom two or three panels were made with a similar amount of camber as the top panels, or entirely flat, then performance to windward would improve even further. In the first post of this thread there two pictures of fan style sails I made and both of them use bendy fiberglass rods. One has camber in all the lower panels but despite using the same bendy battens, it did not bend much. It almost seemed as though the shape in every panel was fighting each other and kept the sail flatter overall. The sail with camber in only one panel bent much more resulting in a continual shape inside of the sails outline. That is something I never saw in the sail with camber in every panel despite using the same bendy battens. This effect may not be as apparent or effective when using rigid aluminum rods, but I am not sure. I realize experimenting with sails on the scale you are dealing with would be time consuming and possibly expensive, however this change was the single biggest improvement I made to my sails. I made a mainsail for my 37' catamaran using the exact same materials and techniques as I did for my junk sails. I used the same bendy fiberglass rods with Home Depot canvas and every panel was totally flat except for one. The leech of the sail ended up having a funny shape and I attribute that to me trusting in the straightness of the edges of Home Depots drop cloth and lofting the entire sail on the docks beside my boat. The edges were not straight. Nonetheless the sail worked well and the shape near the luff was what I intended to create. At one point I used it in 15-20 knots on my way back from Catalina Island to San Pedro. That trip took about 2 hours. I was absolutely flying, it was fun. The sail held together well and no damage was sustained but over time the canvas got moldy. Here are some videos of the mainsail. Unfortunately, I did not record sailing in high winds.

    Testing The Home Depot Sail

    The Outrageous Lady Sails To Catalina Island


    Slieve, I agree with what you are saying. Perhaps my choice of words could have been clearer. Arnes point about the speed of the wind over the sail not being represented by the tell tails was the point I was trying to make. Tell tails are indeed useful tools and important, but they do not tell the whole story. There could be two sails made identically on identical boats, but if one sail is heavily used and the sail shape inside is deformed then a good sailor could trim the deformed sail to have all the tell tails flying, only to still be passed by the other sail. Even though both sails have tell tails flying and were initially made identical, one has slower moving air due to the inefficient sail shape inside the sail. If experimenting, then just having the tell tails flying is not enough information to know whether changes made were an improvement or not. I may have had an advantage on my Laser because I was able to sheet the sail through a single block, often without the ratcheting system engaged. This gave me direct feedback as to whether or not changes resulted in a more powerful sail. Some alterations to the sails resulted in much more of a workout for my arm! With one of my sails, I used the same bendy fiberglass rods for the yard and for the battens. This allowed the yard to bend if not supported. If I allowed the peak of the sail to droop downward too much, then the windward ability was diminished. It looked somewhat similar to the drawing on the right in your sketch. When the yard was supported to keep the peak of the sail more like your drawing on the left, the windward ability was much better. This sail was a precursor to using a more rigid yard and accepting the weight difference for better performance. I attached a photo the droopy sail.


    Paul, the idea of altering your sail to remove the top angled yards and add that sail area to the bottom of the sail leads me to believe that there would be a very cambered panel at the top of your sail. I do not believe that will improve performance, as I believe the top panels should be kept flat, or near flat. Your point that batten pockets and separated panels reducing the amount of good profile shape I believe can be solved by using more bendable battens and less cambered panels. I would also suggest moving the entire sail towards the stern to have less sail area forward the mast if that is possible. I realize that creates more issues with getting the sail to sit correctly but if that can be overcome it may have additional performance benefits, especially if more bendable battens are used.


    Happy sailing!

    -Colin Clayton

    1 file
    Last modified: 01 Jun 2025 20:11 | Anonymous member
  • 01 Jun 2025 14:47
    Reply # 13505383 on 13500036

    Slieve, I think I get what you mean with that sketch: By moving the tip aft, the induced drag is reduced by moving the tip vortex aft. However, I think this would have to be very fine-tuned to generate benefitial effects, and not increase i.e. profile drag. 

    I'm a bit skeptical about the shark fin example: the dorsal shark fin is not a high L/D wing, but a high lift fin with late stalling characteristics (like a fighter jet). The shark needs it's dorsal fins for manouevering, which means generating high lift at high speeds and also at possibly high AoA's. Nature "developed" the adequate wing design for that purpose. If we would use that design for a sail, we would get a wider groove (oversheeting is less dramatic) but loose significant upwind performance due to the bad L/D, wouldn't we?

    Considering a better aspect ratio (higher mast) is not a realistic way to go (though it would be the most effective), what else can be improved? There is one major issue in which the sewn-in, cambered junk rig (and the split rig, too) defers from the bm rig: the batten pockets and separate panels, which reduce the amount of "good" profile shape to about 60-70% of total sail area. Hmmm! Hinged battens with flat sail don't suffer from this, as well as David T.'s wingsail. Taking the wingsail aside, due to its other aerodynamic benefits: would a hinged batten sail work significantly better upwind than a sewn-in camber sail?


    Mauro, that is a great gadget to demonstrate the aerodynamic effects that happen around a sail. It does, however, not give a clue on the significance of each effect. As Arne wrote: it is only one part of the story to have attached airflow, but the question is, how fast is that airflow.

  • 01 Jun 2025 13:10
    Reply # 13505363 on 13500036

    Hi,

    could this help to investigate the aerodynamic of our beautiful sails?

    https://deskbreeze.com/

    cheers Mauro

  • 31 May 2025 11:55
    Reply # 13505145 on 13500036

    Hi Paul, you ask, “would I consider a 30º yard as a fanned top?” Basically the answer is no, but it depends on the length of the yard.

    Pleasexcuse the totally unclear sketch, but the curly lines are a bad attempt to show how the air would leave the left hand rig from the very top, but could curl down the sloping leech in the right hand diagram. Both rigs have the yard at about 30º but the shape of the head is quite different.I believe it is important to push the tip votrex as high and as concentrated as possible. When it curls down the leech as in the right hand drawing it is effectively decreasing the height of the rig and the aspect ratio, and increases the drag.

    Tony Marchaj made reference to the crescent shape of a shark fin and suggested that nature had evolved a low drag efficient shape.

    If I were a few years younger and had infinite patience or funds to pay others I would try to build my ‘ultimate rig’. I believe it would have the bottom batten and the yard the same length, with the jiblet luff and the main leech both straight lines. The yard would be at about 30º and the bottom batten level, and the intermediate batten angles increasing up the sail. The top panel would not be split, but the rest would. The overall balance would be 33%, but might be slightly less at the top and more at the bottom.

    With the Poppy and Amiina rigs I drew the yard shorter for aesthetic reasons, but believe that it is not noticed in practice.

    I realise this posting may raise a few eyebrows, but perhaps that is a good thing.

    Cheers, Slieve.


    1 file
    Last modified: 31 May 2025 23:06 | Anonymous member
  • 31 May 2025 09:59
    Reply # 13505138 on 13500036
    Anonymous member (Administrator)

    The speed of the airflow on the leeside of the sail 

    Over the years, Slieve and I have had a quiet little disagreement regarding the shape of the forward part of our sails. While he has focused more on having a clean, rounded leading edge, which eventually resulted in the SJR, I have relaxed and (too?) boldly claimed that as long as the telltales at the leech fly, the airflow on the leeside of the sail must be fine.

    Only recently did it dawn to me that I might be wrong, or at least only half-right on this. Sure enough, the flying telltales indicate (re-)attached airflow, but they say nothing about the speed of it. When looking in the books, it is clear that the airstream on the leeside of foils speeds up, and thus produces well over half of the foil’s total lift.
    It could therefore well be that the SJR or David Tyler’s soft wing JR (with the mast hidden inside), will produce a higher windspeed on the leeside, and therefore more drive for a given sail area.

    However, this is not easy to measure, so it will have to be guesswork from my side.
    I can only state from practical JR sailing, first with a flat sail and then with my plain cambered sails, that the wide performance gap, when close-hauled, between the Bermuda rig and the JR, has almost been closed. It will take a lot of effort to improve the VMG to windward with another 3-5%. Not a project for lazy old me.

    Cheers,
    Arne

     


    Last modified: 01 Jun 2025 11:23 | Anonymous member (Administrator)
  • 30 May 2025 19:15
    Reply # 13504943 on 13504706
    Anonymous wrote:
    Mauro wrote:

    Arne,

    on my sail (20,4 sq m Johanna style with 70 deg yard angle) the top panel have less camber than the lower ones. I am really happy with my/your sail. Nevertheless the two top panels inflate but their tell tales seem to look mostly to the lee.
    Is my sail wrong? Are there any tricks to control the twist at the top of the sail? If not, don’t you think that a fully cambered upper section would have a better angle of attack and thus an improved air flow and more lift? 

    Cheers 

    Mauro



    Mauro,

    yes, it could be that you have too little twist in your sail. In my Ingeborg I have the Johanna sheeting with its strong anti-twist. With this setup the two top panels stall a moment before the panels lower down.
    However, with one or two reefs, they seem to stall at the same time as the lowers. To me, that is a good compromise.

    Maybe the Pilmer sheeting with slightly less anti-twist in it would work better for your sail?

    Arne


    Thank you Arne, as usual you are plenty of good ideas!

    I will search for the Pilmer sheeting in your files and see…

    Cheers 

    Mauro

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