SJR for "Cirrus" State of the Art and Next Step?

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  • 20 Jun 2019 22:15
    Reply # 7591071 on 7584488

    Thank you for the feedback. I think I will go with a four panel design (updated pdf below) to reduce the weight and complexity. Three levels of reefing is plenty and I will use lazy jacks and a sail bag arrangement to keep the reefed panels out of the way and tidy.

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  • 20 Jun 2019 15:48
    Reply # 7589630 on 7588575
    Deleted user
    Graeme Kenyon wrote:

    I pointed out the long thin panels merely as a point of difference, and have no idea if aspect ratio of jib panels is significant. I had correspondence with Slieve some time ago in regard to scaling up an Amiina rig for a larger boat and I got the impression that he felt the aspect ratio was about right, and I was not encouraged to change it. I did wonder if there would be any significant loss from your having two low aspect jibs instead of a single larger one with the same area. I have a feeling that the right answer to this question is: no-one really knows until someone tries it.

    My intuition tells me that many small panels would be less efficient than a few larger ones.  More weight of battens, more sewing, and more of the airflow past the luff is in transition from shelf foot to middle section of the panel, more turbulence. 


  • 20 Jun 2019 00:42
    Reply # 7588575 on 7584488

    Robert you seem to have thought your way through this better than me and I would like to revise my initial comments about your sail area, which of course is a matter for you to judge for yourself. I suppose I was berating myself rather, because I think I made my mast and battens are a bit too heavy for my boat, and I think I could have made my sail a little less in area – and I was comparing my rig to the very light weight Bermudan rig it replaces. Still, not a bad idea to keep these things in mind. I wish I could afford carbon fibre – and I do intend to try to find lighter battens. (Mine are made from solid timber, same as River Rat. I am wondering now about bamboo.)

    From David W I can see now the special advantage of a hinge-tube mast arrangement when it is applied to a trailer boat – the ability to leave the rig in place, below the hinge, when dropping the mast. I can’t yet think of a way of matching that luxury. My mast is walked up from the heel in the same manner as you (Robert) are proposing, and it is so simple, easy and economical it is the one detail I am pleased with and don’t want to change. Anyway, if you can manage the mast and sail together like David D describes, then I guess you guys will get the best of both worlds. Marcus (with Freebie) tells me that he lifts out the complete rig and stows it all in one bundle (but still tends to have a bit of untangling to do at the launching ramp.)

    One thing I did not understand: your concern about “stagger” when reefing. I am not sure if we are talking about the same thing, but  – perhaps it is to do with having a vertical mast and very small batten rise, I do not know - but when I drop my sail, fully or partially, it behaves delightfully well, way, way better than any gaff or Bermudan rig I have had before - and the battens stack up with barely any stagger at all. I can’t see why yours would be very different.

    I pointed out the long thin panels merely as a point of difference, and have no idea if aspect ratio of jib panels is significant. I had correspondence with Slieve some time ago in regard to scaling up an Amiina rig for a larger boat and I got the impression that he felt the aspect ratio was about right, and I was not encouraged to change it. I did wonder if there would be any significant loss from your having two low aspect jibs instead of a single larger one with the same area. I have a feeling that the right answer to this question is: no-one really knows until someone tries it.

    Last modified: 20 Jun 2019 23:19 | Anonymous member
  • 19 Jun 2019 17:37
    Reply # 7587937 on 7584488

    Hi 

    Thank you for responding to my post. I had considered a hinged mast and if the final sail design means that the mast position has to move forward again I think I will use this option. In the current position the mast can be raised by positioning the heal and walking it up to the vertical. This seemed to present the simplest solution but fixes the position which is intimately tied in with the sail size and configuration.

    My intention is to keep the sail bundle and associated rigging attached during the mast raising and lowering by designing a bag that can keep the sail and battens under control. Now that I am thinking about batten sizes and materials I am realising that a Junk sail does have a significant weight which I hadn't totally appreciated. Thank you for highlighting this.

    I have worked out the sail size and balance by aiming to keep the centre of effort in the same position as the current rig. i.e. if the mast moves forward the sail area reduces and vies versa. I was also looking for a bit more sail area on the basis that it could be reefed easily. So a good challenge on the size of the sail, I wanted more but this mast position does result in plenty of sail area. I am not sure that it is fair to go back to John Welsford though. I am sure that he will have designed the current rig as his best compromise that can be used by a wide public. The obvious answer to the question of "is this rig too big" is "yes". I am designing this rig for me and taking the personal risk with the design. When the boat is sold on it can go with the existing gaff yawl rig as John intended. From my perspective I would like a little more drive than the current jib and mizzen provide on their own which is why the top panel is bigger than usual and incorporates the area of what would have been the second panel(I thought I was also saving a batten). I had been rationalising the overall size of the sail on the basis that it would be good in light winds and easily reefed. Is this how it works in practice? I find the current gaff main difficult to reef on the water and easy reefing is a prime objective.

    I had been pondering the amount of mast I needed above the yard are there any rules of thumb for this? There is currently about 0.6M available in this design.

    The boom height above deck level has been set at half the panel height and the 5degree rise should mean that it will miss heads of the crew. There is space and access to mount blocks etc at the base of the mast below deck level.

    The panel height had been worked out on the basis of minimising stagger of the reefed sail as I estimate there is only just enough space between the end of the battens and the stern of the boat where the sheets can be secured. This is why I have long thin panels. I am wondering how significant the 1.1 aspect ratio of the jiblets is? I had not thought about this, should this be the overriding consideration for the minimum panel height for a SJR?

    Thank you for the link to the sail balance, mast position, slot width thread. I had missed this exchanged and it helps me.

    Last modified: 19 Jun 2019 17:40 | Anonymous member
  • 19 Jun 2019 07:27
    Reply # 7587118 on 7584488

    Hi Robert, 

    On my Wayfarer, the steel structure into which the mast fits was designed to fit into the original tabernacle for the bermudan mast. On both the bermudan rig and the junk mast/steel structure ,a pivot pin below deck allows the mast to be  lowered and being fairly light can easily lowered by hand.

    But, all the various lines associated with the split rig certainly don't make for a quick-rigging possibility if you have to disassemble it for trailering and reassemble again to sail. Takes far too long.

    So it's definitely best if we can keep the rig assembled on

    the mast when transporting.

    With my setup, Im going to put a running line on the front topping lift, so I can release it when I want to lower the mast and bundle. 

    This will allow the lowered and tied-up sail bundle to pivot as I lower the mast in the tabernacle onto a small mast crutch at the stern. I will then be able to remove the mast pivot pin and stow mast and sail bundle (all tied together and without disturbing any of the rigging lines) inside the boat for road transportion.  

    It should then just be a matter of fitting mast and sail bundle back in tabernacle, installing pivot pin, untie sail bundle from mast,  (in my case, then attach side shroud wires to steel support and boat) raise mast (attach front shroud to steel support and tension),  adjust front running topping lift   and raise sail to ensure nothing is tangled prior to launch and go sailing.

    Hopefully it will be quicker to do than it took to write it on the phone.

    Dave D.


    Last modified: 19 Jun 2019 07:30 | Anonymous member
  • 19 Jun 2019 04:33
    Reply # 7587010 on 7584488

    Robert,

    on my boat Gypsy Rose (25 feet long trailer sailer) I have a standard cambered junk sail but have a mast with a hinge about 750 mm above the deck and a sliding sleeve that drops down to give the mast stability when it is in the raised position. This had allowed me to drop the sail bundle below the hinge, raise the sleeve and drop the mast in about 15 minutes. Raising and rigging the mast and sail should not take much longer than this but I have yet to try it. The only lines that I need to derig are the topping lifts, which I use to raise and lower the mast sleeve. On your much smaller boat a similar hinged mast could be installed and would allow for quick and easy dropping of the mast while allowing the sail bundle to just drop down with no or very little derigging. I intend to put a similar system on my other boat Little Gypsy Girl, which is rigged with and aero junk sail. I anticipate that I should then be able to rig/derig her in about ten minutes.

    I constructed the hinge from aluminium tube and flat plate and it is strong and stable when raising and lowering the mast. I assume that your mast is wooden? If so then a short length of tube fitted to the two sections of the mast (after it is cut at the hinge location), a fabricated hinge made from sections of aluminium plate and a slightly larger section of pipe as a sleeve and you should have a workable solution to your challenge.

    All the best with the project. David.

  • 19 Jun 2019 02:22
    Reply # 7586874 on 7584488

    Robert

    Your request for feedback deserves a response and as none of the split rig aficionados have yet done so, here are a few comments in the hope of provoking some further discussion. I have recently made an experimental SJR for a trailer boat about the same size as yours, motivated by the same objectives as you have listed and am just a little further down the track than you.

    Your second objective (to be able to rig the boat and be up and running in 20 minutes) is where I am stuck at the present time. My goal is 10 minutes. I have not yet achieved even 20 minutes, but still working on it. Evidently the junk rig sits more happily on a moored boat, where time can be spent setting it up initially, whereafter it can be left in its stowed position, ready at all times for a quick hoist. Whereas, a trailer boat of 5 or 6 metres is just at the awkward size where the complete bundle of mast, sail and battens is getting a bit big and unwieldy to strike and keep together as one package. The need for partial or complete disassembly and reassembly between launches, requires a bit of extra thought. Sure, the free standing mast goes up in a jiffy, but from there on things slow down a little. In the words of Phil Bolger, there are a lot of sticks and bits of string and while the JR has some undoubted advantages, for a trailer boat: getting away smartly at the launching ramp appears not to be one of them. I hope to find a way, and will be interested to know how you get on.

    Slieve, the originator of the rig on Poppy, together with Edward on the Amiina, have made a short sequence of developments resulting at present in the very parameters you have adopted for camber, sheeting angle and batten rise so I presume you are familiar with Slieve’s writings, and up-to-date with his later developments. Slieve is the obvious go-to person for discussions about further development, although there are others emerging. Also James on River Rat and Dave D. who has converted a Wayfarer have both helped me with comments which relate especially to SJR on their small trailer boats.

    Merely copying what others have done successfully is the safer way, which is what I am doing, but with your proposed sail plan you are, as you say, experimenting a little. I have been very interested in the changes made to Amiina’s rig between the MkI and MkII versions, as they are evidently based on experience and reported to have resulted in an improvement. I note that apart from increasing camber and sheeting angle of the jibs, they decreased the over-all sail area, changed from 5 lower panels to 4, but maintained the sail’s proportions, in particular the ratio between height and width of the jib panels (a ratio of 1050/940 = about 1.1)  - whereas on Cirrus you are proposing 5 relatively narrow panels, with somewhat unusually proportioned jibs (height to width looks like about .75) and a very large top panel. I would be interested in your reasons for trying this.

    I am not at all sure about your suggested batten-to-batten jib leech stiffener, perhaps you should wait and see if there is any need. You may have noticed from photographs that Amiina now carries a tiny sail batten on each of the jibs, which each have a light, standing sheet back to the mast. I am not sure if this slight extra complication has been added to improve performance, or whether it is to overcome a problem from the increased camber and sheeting angle, as it is a slight departure from the KISS principle advocated by Slieve. I copied the Amiina MkII sail design and so far the jibs seem to set quite well without them, but there is plenty more I have yet to learn.

    Slieve has always advocated moderation in sail area for the SJR. Some of us have fallen for the temptation to increase sail area. I confess to it, and I suspect James might have done the same (we will see, I am hoping James will post a report when he gets back from his coastal voyage to the recent AGM.) I think Slieve is going to be proved right, in the end, on that point. I think you have gone for too much sail area. After making a free standing mast, SJR sail and a set of battens, I am astounded at how very much heavier the whole bundle is, compared with the rig it replaces. I am now sceptical of the oft quoted adage that you can pile on sail area and the weight aloft and the relatively high centre of area of a junk sail “does not matter because it comes down when you reef.” That might be OK up to a point with a shorter mast and high peaked yard, but not backed up by any calculations, this seems to me to be a rather imprecise statement and might be worth re-considering, or toning down, in a small boat which is easily capable of capsizing. You are an experienced dinghy sailer and I suppose you are looking for good light weather performance. Still, I wonder if it might be an idea to contact John Welsford, the designer of your boat (which you can easily do) and see what he thinks about your proposed small increase in height and possibly not so small increase in weight of the mast and spars, together with your substantially increased sail area and its substantially higher disposition.

    I made the mistake initially of placing the yard too high and had insufficient halyard drift. It looks as though your proposed rig is a bit the same. On the subject of drift, I also initially over-looked the requirement for sufficient drift below the boom. In order to reef with the spanned running parrel/downhauls, you need a drift down there of at least half a panel width plus a little more. It looks as though you will be able to place the turning blocks below deck level, so perhaps not an issue in your case.

    Your suggestion of making the slot as 6% of chord length yields, in your case, a slot width of about 20cm or 8” which seems unusually large. You might be advised to check with the others before doing that. I think (from memory) Slieve has spoken of using mast diameter as a guide, which might give something like 10 or 12 cm in your case - and I note the slot on Amiina is 15 cm. I don’t know how important the slot width is, but it has been found in the past to add a little confusion to the definition of "balance" when applied to a split rig - with unhappy consequences in at least one recorded case. You probably already know that it is necessary to include the area of the slot together with the "area of sail in front of the mast" when doing the calculation. This so-called “balance” (a misnomer in my opinion) is a sensitive area which has provoked discussion and was perhaps a little ambiguous in the draft notes which Slieve provided. Slieve has since clarified his method for placing the mast in relation to sail area, in a forum post here, dated 24 May 2017 and I presume you are aware of that, and not experimenting too much with that.

    I don’t think anyone has advocated the classic “slot effect” theory as a reason for the split rig, and I don't know much about it it, though I can point out to you that accelerating the speed of air flow over a surface results in a reduction, not an increase in pressure. Slieve has given a clear explanation of his reasons for developing the rig and he is happy with the results while acknowledging that other junk rig developments in other directions are also proving to be successful. The SJR (and aerojunk) rigs do give another option regarding mast placement, and do appeal to those who like to experiment.

    Best of luck with your conversion. I look forward to your results and I hope some of the of the others who have already built functioning small-boat SJR rigs will chime in.


    Last modified: 19 Jun 2019 06:29 | Anonymous member
  • 17 Jun 2019 22:56
    Message # 7584488

    Hi

    I have a John Welsford Pathfinder cruising dinghy (Cirrus), to which I am adding a SJR.

    The dinghy is currently rigged with a gaff yawl which looks great and sails well. My objectives for adding the option of a SJR are:

    • Position the mast so that is can be raised and lowered quickly and easily 
    • Be able to rig the boat ready to go in less than 20 minutes
    • Be able to reef very quickly and easily
    • Find out how it sails with a SJR vs the gaff yawl arrangement
    • Enjoy a bit of play value working out how SJR works and trying a few experiments
    • Develop a relaxed cruising rig to support messing about in boats

    Over the last winter the mast has been strengthened, partners have been modified to take the new mast position and a new mast step has been put into place. Now that the summer is here the boat is back on the water with the current Gaff Yawl set-up but I am thinking about the next step in the project and making the sail. The attached pdf shows the general design that I have in mind, overlaid against the existing sail plan (I am keeping the mizzen because I like it, although I am still working out what it does when i'm sailing, it is definitely useful when stopped).

    From reading through the SJR posts I have gathered the following impression on the current state of the art for SJR sails:

    Light weight ripstop cloth is fine (2.2-3.8Oz). I will be day sailing inshore

    Jiblets- camber 10% and sheeting angle 12degrees, Max Camber @37%

    Main Panels - Camber 7%, max Camber @37%, final 50% as flat as possible

    The sail design has battens that are 3.4M long with a rise is 5degrees. The yard is @ 35degrees with 33.5% balance . This level of sail balance plus the mast position, I can accommodate, should keep the boat balanced without increasing the weather helm (according to my calculations anyway). In fact its the position of the mast that I want which drives the type of Junk Rig sail that fits the boat.

    As this isn't a big expensive boat and I can always sail around with the existing rig for a bit longer if an experiment doesn't work out, I am willing to try out a few suggestion for how SJR could be improved, on this sail.

    However as I have only seen a SJR in pictures I thought I would ask the question of those of you who actually have a working rig.

    What do you thing the next development steps should be?

    Thoughts in my mind are:

    1. I'm not clear on the optimum slot size. I have seen 6% of the total chord stated?
    2. With a light sail cloth would it help to fit the leech of the jiblets (batten to batten) with a flexible stiffener that would hold a curved shape?
    3. Are horizontal battens on the jiblets worth considering?
    4. I am also struck reading posts on this site how people with traditional Junk rigs don't see any difference in performance between port and starboard tacks. I am not totally convinced by the slot effect explanations of jibs scooping up air and increasing the airflow over the main (more air on the low pressure side of a sail sounds like less pressure differential). If the function of a sail is to create a pressure differential why have a hole in the middle of it to let air through? May be most of the SJR advantage comes from the balanced sail and projecting the luff forward into clear air. Is this a daft idea?
    Any other thoughts on refinements to a SJR that I should try and report back on?



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    Last modified: 18 Jun 2019 16:57 | Anonymous member
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