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SJR

  • 10 Apr 2026 16:56
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    Reply # 13619247 on 13618156
    Anonymous member

    Jan, for 'gig' read 'rig'. It was a typo which I have corrected.

    S
  • 10 Apr 2026 16:10
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    Reply # 13619208 on 13618156
    Anonymous member

    Thanks for your reply, Slieve!

    I'm honored that you've given me a moment's attention. To be honest, I was kind of hoping for it ;-)

    I have to admit that after two seasons of sailing, I have a growing respect for junk sails, and the SJR in particular. I agree that Graeme is right when he says that every detail in this sail is well thought out.

    My previous sail (the origami SJR) didn't have a toppanel. This was partly due to laziness, partly because I didn't really know how to design a toppanel at the time, and partly just for fun – I wanted my folding dinghy (2.5m) to look like a square-rigged ship from a distance.

    Graeme mentioned something about overbalancing back then, but in my on-shore tests, it didn't occur, so I didn't worry about it. The sail's balance (measured from the photo) was 390/1140 = 0.342, but as you can see, the gap is quite large, and there's also a gap between the main luff panel and the mast. There are also gaps between the battens and the horizontal edges of the jib (and main) panels.

    However, the sail I'm sewing now is different. I'm trying to make it as close to your description as possible. I made a test panel from leftover tarp from a previous sail and noticed overbalancing, a description of which I found while digging through the forums last winter.

    The new panel has a balance of 550/1800 = 0.305. So I added a test top panel (made from a newspaper) and the overbalancing disappeared. The top panel caused the center of the sail to shift further aft. That's logical.

    I'm finishing sewing the new sail, so I'll definitely test it on land. I'll shorten the jibs along the battens as needed.

    By the way, what did you mean by "gig"? In dictionaries/online, "gig" means a rowboat...

    Thanks again for your helpful comments. Cheers - Jan

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    Last modified: 10 Apr 2026 16:38 | Anonymous member
  • 10 Apr 2026 13:32
    Quote
    Reply # 13619151 on 13618156
    Anonymous member

    Hi Jan,

    You're nearly there.

    What I said was that the mast centre line should be between 280 and 350 units from the luff of the jib for a 1000 unit jib luff to main leech rig, and 333 units being the suggested normal.

    And the luffs of the main panels are in line with the  mast centreline and the split is from the jib leech to the mast centreline. This dimension may depend on the diameter of the mast.

    By the way, the latest rigs all use 5 degrees as the batten rise as with the greater balance there is little risk of the rig dipping in the water when heeled. The yard is 30 degree as you say.

    I hope this helps.

    Cheers, Slieve.



    Last modified: 10 Apr 2026 15:59 | Anonymous member
  • 10 Apr 2026 01:30
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    Reply # 13619030 on 13618156
    Anonymous member

    I hope that using this simple drawing, it would be possible to clearly determine the parameters (especially the balance) of the standard SJR sail (as we now imagine it).

    Let's assume that dimensions are along the batten (x axis), where zero is the jib's luff and 1000 is the mainsail's leech. So:

    1. The distance from the luff of the jib to the mast center should be no greater than 330?

    2. The gap of the main should be zero?

    Am I understanding this correctly?


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    Last modified: 10 Apr 2026 08:16 | Anonymous member
  • 09 Apr 2026 17:42
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    Reply # 13618857 on 13618156
    Anonymous member

    Thanks for your response Graeme, it’s fairly up to date.

    There are potential problems with a split in the top panel, and advantages with no split so the recommendation is no split.

    I’m not a fan of ‘slot effect’, and feel it has little effect when there is no sail overlay as with a genoa and mainsail.

    My latest recommendation is to place the rig outline on the side view and then place the mast, and luff of the main panels, somewhere between 28 and 35% overall chord, though the higher the better. This gives some flexibility in fitting the mast around the internal furniture or deck hatches. I think Poppy had only 30% balance and it was only after I had built that rig that I met Roger Stollery who had run a set of experiments on balanced rigs on model yachts that I learned the 33% area rule. The second SJR had 35% luff to leech balance and was a great performer and as the main panels are taller than the jibs then it was within the 33% rule.

    Graeme you are right in saying that the plan form, mast height and yard angle are also important.

    As for testing the rig, that is what the Round the Island racing was all about. The SJR was not designed as a racing rig, but as a better cruising rig, but has been criticized for being a racing rig because I used that to compare with other boats. It is a pure cruising rig with performance, safety, ease of use for weak/ light crews, low stress and low cost when compared to its Bermudian cousins. What more can you ask for?

    Cheers, Slieve.

    PS. Don’t forget that I’m biased.
  • 09 Apr 2026 13:19
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    Reply # 13618724 on 13618302
    Anonymous member (Administrator)
    Anonymous wrote:

    For example, I'm wondering if it wouldn't be worth trying to place wind indicators on the entire sail, like in this video (e.g., at 8:00 or later). Maybe that will clarify some of our questions (and probably raise a few new ones).

    Bonjour

    It is interesting to place wind indicators on the entire sail in the trial period to balance the incidences of the giblets and the main pannels. It is also interresting to check or tune the sheeting system.

    Once the sail tuned, as there is no way to adjust the camber or the incidence of the various parts of the sail,  the important wing indicators are on the forward part of the giblets to monitor the incidence of the sail.

    Eric
  • 08 Apr 2026 15:58
    Quote
    Reply # 13618302 on 13618156
    Anonymous member

    It's definitely a good topic for discussion. The problem is, I need to finish sewing a new sail, and I've been really lazy this winter.

    I really like the SJR and think there's no better sail for me. So for now, following your advice - I won't split the top panel.  I hope someone will test and measure all SJR aspects someday.

    For example, I'm wondering if it wouldn't be worth trying to place wind indicators on the entire sail, like in this video (e.g., at 8:00 or later). Maybe that will clarify some of our questions (and probably raise a few new ones).
  • 08 Apr 2026 10:28
    Quote
    Reply # 13618182 on 13618156
    Anonymous member (Administrator)

    Regarding a split in the top panel, the sail that Slieve designed for Amiina (the Mkll sail) did have a split top panel. Slieve says that it was a lot of extra trouble for no measurable gain in performance, and for that reason these days advises not to bother with the split in the top panel. I don't think there is any need for it myself. My Amiina Mkll sail has no split in the top panel and it works just fine.


    While on the subject, I don't believe the much vaunted bermudan sloop "slot effect" really exists in a SJR.

    I think people focus too much on the split. I don't believe the split contributes anything much in itself - what it does do is allow a high balance (which some people prefer, and which sometimes allows a more convenient mast position). Arguably, it allows a more perfect leading 1/3 of the sail (the important part to windward) and in addition the sail shape is not deformed by the mast on either tack (although the "bad tack" notion has pretty much been dismissed). Furthermore, unless the sail has a full 33% balance (but no more than that) then one has to question whether there is much point in a split sail at all, since higher-balance contiguous sails are starting to become proven these days.

    There is no doubt that the near-perfectly harminised Amiina Mkll sail is proven to be a well-behaved, easily managed and good performing sail - I wouldn't swap mine for quids - but this is due to the complete package, in particular the planform shape. If the yard angle is wrong or the mast is not tall enough, or any other variation, then all bets are off. These are more important considerations than whether or not the top panel is split. That's my tuppence worth. 

    Last modified: 08 Apr 2026 22:30 | Anonymous member (Administrator)
  • 08 Apr 2026 09:47
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    Reply # 13618179 on 13618156
    Anonymous member

    Thanks for the reply, Paul!
    Since my question wasn't directly related to the previous thread, I've removed it from that thread.
    But I'm glad you replied about your experiences with the SJR sail (and sewing it from tarp), as I've been wanting to ask you about it for a while.
    As for sewing SJR sails from tarp, that's what I'm doing.

    As for splitting the top panel, I think I'll have to try it myself.
    I suspect splitting the top panel might not be advisable, as its role is (probably) to improve the sail's balance, among other things. Splitting the top panel probably worsens that balance.

    I'm currently making a top panel (unsplited), hence my interest in splitting it.
    If I'm enthusiastic enough, I might try splitting it someday.

    Regards- Jan

    Last modified: 08 Apr 2026 09:55 | Anonymous member
  • 08 Apr 2026 06:14
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    Message # 13618156
    Anonymous member

    Hi Jan,

    I’ve replied to your post here.

    The polytarp I used for my experiment has held up well considering it’s only held together 

    with gorilla tape and single stitching. I only needed it to last long enough to establish whether 

    SJR would be viable for both sails on a Schooner so didn’t take any care in the construction.

    I had hoped to have made the new suit of sails by now using posher cloth but haven’t had the time, however I’m getting on with it now.