Sail Balance - Position Relative to Mast

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  • 13 Dec 2019 23:38
    Reply # 8270509 on 4793670

    The posting I have just put on the 'Split or unsplit, that is the question' thread might have been more useful if posted here.

    Cheers, Slieve.

  • 10 Dec 2019 22:31
    Reply # 8238528 on 4793670

    I didn't say the sail hangs from the yard, I said it hangs from the top batten. With a little bit of judicious tuning, yard slingpoint etc. you can get by with the minimum of hauling forces, for me it was one of the attractions of the Amiina rig. Dave Z describes his top panel as a "headboard" - that's a useful paradigm.

    (By the way, if you want to experiment with top panel shapes, vis-a-vis "drape", rather than spend time with stick-and-string models, I read a suggestion somewhere (it might have been Slieve) that you could build the lower sail and hoist it without the top panel, and instead of the top panel just have a ropes where the proposed luff and leech of the top panel would be. Try different positions on the yard, and different yard angles etc, until satisfied you have the drape about how you like it, then build a top panel to that shape. I thought that was quite an interesting idea but I don't know if anyone has tried it.)

    Last modified: 10 Dec 2019 22:50 | Anonymous member
  • 10 Dec 2019 22:23
    Reply # 8238437 on 8237954
    Anonymous wrote:

    It hasn’t been done before on a SJR (as far as I know) and when you stop to think about it, it vastly complicates the design. Unless you use the vertical drawing and then just tilt the whole thing just a very small amount. Why bother?

    Tilting the whole thing is how it's done as far as I'm aware. I find it hard to believe that the SJR hangs from the yard naturally aligned in its final intended position, junk rigs in general when hung from the yard without any supporting rigging tend to hang forward of the mast so you need various parrels to "pull it" aft to its intended position.

    If you had a sail with 50% balance and hung it with the yard attached in the middle it would hang pretty straight but this is not the case with Poppy's sail at least.

    Why bother? Because one highly appealing aspect about the junk rig for me personally is that with a forward raked mast the sail will "push" itself out in ghosting conditions (esp. with the wind abaft the beam), something which is a huge annoyance with bermudian rigs flopping about.

    It just happens that gravity is a vertical force. Not having "come up through the ranks" of conventional junk sails, getting a junk sail to set nicely is something I don’t know much about, but my gut feeling is you might be diminishing a rather significant advantage, in order to gain a different very small advantage, and simply adding an unnecessary complication. I am not sure, I don’t know enough. Give it a try!



    I will! :) I have in fact just purchased some sticks and strings and will be building a model rig soon. There is surely a point where adding more rake will start causing issues but I don't think something like 1-3% would cause any. I might be wrong though. And I would love to be enlightened if someone here has any good input on the matter. And however that may be I might have some answers myself soon.



    PS. This WYSIWYG editor is driving me crazy.

  • 10 Dec 2019 21:18
    Reply # 8237954 on 4793670

    What would be the problem(s) with raking the mast a degree or two forward?

    It hasn’t been done before on a SJR (as far as I know) and when you stop to think about it, it vastly complicates the design. Unless you use the vertical drawing and then just tilt the whole thing just a very small amount. Why bother?

    When I first tried to set up my rig I did it with the boat sitting on a trailer, and forgot that the trailer wasn’t level (the bow was pitched up a bit). Silly me. I had all sorts of trouble.

    The thing is, the current SJR designs are all intended to hang nicely from the top batten with minimum hauling to get the sail into shape. (It was one of the goals that Slieve was seeking. I call it the “drape”). It just happens that gravity is a vertical force. Not having "come up through the ranks" of conventional junk sails, getting a junk sail to set nicely is something I don’t know much about, but my gut feeling is you might be diminishing a rather significant advantage, in order to gain a different very small advantage, and simply adding an unnecessary complication. I am not sure, I don’t know enough. Give it a try!


    Last modified: 10 Dec 2019 21:26 | Anonymous member
  • 10 Dec 2019 17:51
    Reply # 8236293 on 8198199


    Thanks for the clarifications Graeme!

    Problem is then how you would properly establish the CE/CP in order to get the correct lead (another fuzzy concept) for the rig. There is nothing difficult or “fuzzy” about this, other than the need to realise that there is no such thing as an actual centre of effort or centre of pressure.

    In regards to "fuzzy" this was exactly what I meant, that we calculate lead based on CLR and CA (center of area, not center of effort/pressure) and that this is a huge simplification since the actual CLR and CE start changing as soon as the boat starts moving. Experienced designers end up making an educated guess with lead based on hull shape, type of keel/rudder, type of rig/sails etc, all of these coupled with experience. The recommendations in PJR assumes flat sails so the best for those who have cambered sails is to read up on other junkrigger's experiences and then make educated guesses ourselves. I think that falls into the definition of "fuzzy". :)

    Anyways, it's not highly relevant to the discussion here.

    I'm considering converting my current boat to split junk due to the split (or aero) allowing the most balance and thus the best mast position without having to make considerable modifications to the interior. From some quick sketches I would need something around 33-35% (including the slot).

    Now, that makes sense and I think you are on the right track. Assuming you are converting from bermudan rig to any of the well-proven junk variants, I am sure you will be delighted with the result, best wishes.

    Thanks! This will in fact be my second JR conversion. The previous one was in 2015 where I was first going to build a wingsail but in the end - due to lack of time - opted for a flat sail with hinged battens. This worked quite well and I was happy with it but ended up selling the boat shortly after due to moving abroad because of work.

    I've been aware of the SJR ever since I got introduced to JR back in 2010 or so but back then I believe Poppy was the only one sailing but now over the years the SJR seems to have caught on and established itself as a quite well working rig.

    As my life situation has changed again and I now have the opportunity to mess around with boats and rigs again I ended up buying a 28 footer (similar size to my first conversion) last summer. With a traditional JR the mast would end up right in the middle of the V-berth, which is what I did with my last conversion, but I don't want to do it this time around - I would like to keep the mast as close to the original (keel stepped) mast position as possible, thus keeping the accommodation more or less as-is. And to achieve this I don't see many other (or better) options than a "highly balanced" rig, of which the SJR seems to make the most sense. I've sketched various multi-masted rigs but haven't really been happy with any of them, so at this point SJR is the most likely candidate.

    A small disadvantage of the SJR rig is that, so far at least, they have all been designed around an assumed vertical mast, for obvious reasons of simplicity - so with the split rig we don't get that extra, little benefit.

    Why is this though? At least it's not obvious to me. What would be the problem(s) with raking the mast a degree or two forward?

  • 08 Dec 2019 23:19
    Reply # 8218213 on 4793670
    Anonymous member (Administrator)

    Robert,
    you are quite right that Johanna-version the H-M sail with 70° yard will retain the high-peaking yard, even with only three panels set. I cannot tell if this is better than a flat-topped sail ( since I haven't sailed with a flat-topped sail), but I surely can tell you that the 3-panel top section is surprisingly powerful and close-winded. That lead to my slightly cocky write-up, last summer...

    Arne


  • 08 Dec 2019 21:20
    Reply # 8217399 on 4793670

    Comparing split and unsplit is probably getting a bit off-topic and it wasn’t my intention to open that up. But you make some very good points Arne and although I am not qualified to make comparisons, it’s a discussion I sure would love to have with you because I thought long and hard about building one of your rigs and sincerely wish I had the time and the years left, to do so. So much still to learn… so little time! Obviously, Robert is interested in this question too. I’ll be bold and open up a new thread.


  • 08 Dec 2019 17:34
    Reply # 8215877 on 8214413
    Anonymous wrote:

    Graeme

    I guess I have three reasons for sticking with the un-split Johanna-style rig.

    Arne

    There may be another reason, although as yet untested. That is when reefed down. High angle yard vs low angle yard. First you have to accept that high(er) aspect ratio confers greater lift/drag ratio and greater lift/drag ratio confers greater windward speed. Think fin keel vs long keel, bermuda rig upwind vs junkrig upwind. A 70 deg yard rig like Arne's, when reefed to 1,2,or 3 panels will have a higher aspect ratio (max Ht^2/area) than one with a flatter yard angle, everything else being equal. For example the SJR sail plan below with a 40 deg yard:

    AR full sail 2.4, 3-panel 1.4, 2-panel 1.1

    Compared to my estimates from CAD for the Ingeborg sail plan:

    AR full sail 2.4, 3-panel 1.6, 2-panel 1.7

    Question: is the difference trivial?

    The compromise is that with the high AR rig: more parrels, more lines underfoot in the cockpit, more tweaking. There is always a compromise.

    robert self


    Last modified: 08 Dec 2019 17:42 | Anonymous member
  • 08 Dec 2019 13:53
    Reply # 8214413 on 4793670
    Anonymous member (Administrator)

    Graeme

    I guess I have three reasons for sticking with the un-split Johanna-style rig.

    ·         It is faster and more forgiving to produce. Each panel of the SJR has two luffs. To keep both luffs straight, both has to be exactly the same lengths (..however, as I write this, it strikes me that one could possibly adjust slack luffs with a quick lashing...).

    ·         I am unsure if the SJR is any faster to windward than the Johanna JR ( or any one-piece, cambered JRs). My experience is that the Johanna JRs are just about as close-winded as Bermuda rigs. The split JR may well be more powerful over-all, but being a fjord sailor, my first priority nowadays is on VMG to windward. Any JR do well when reaching and running.
    Note: I said I was unsure. One day it may be proven that the SJR outperforms a well-made, ordinary cambered JR to windward  -  or not.

    ·         The 70°, full-length yard ensures a long luff and maximum sail area on a not so tall mast. With all the bridges in my area, it makes sense to avoid tall masts. In addition, in the summer season, we often have quite light winds early in the day, so a decent sail area is very welcome.

    Finally, what you describe about downwind sailing in your PS; echoes what Slieve McGalliard once told about his Poppy.

    Arne


    Last modified: 08 Dec 2019 15:55 | Anonymous member (Administrator)
  • 08 Dec 2019 12:39
    Reply # 8213930 on 4793670

    My (armchair) idea was just that if the jiblets grow until the sail approches the point of instability, the sheeting angle and camber of the jiblets may play in.

    Hi Arne you may well be quite right about that.

    When you gradually head up into the wind with Serendipity, which part of the sail appears to be luffing first  -  the jiblets or the mainlets

    The mainlets seem to luff first, while the jibs are still drawing well. The mains have turned out very full up near the luffs (to me they look good) . I find if I ignore it and just sail by the jib telltales, the boat goes well, though I can’t say it points up into the wind particularly well, just OK. I suspect I am not getting the best out of it. But I am content. If I keep coming up into the wind the jibs begin to collapse and by then the mains are definitely luffing. All this takes place in quite a narrow window though, just a few degrees. The "sweet spot" for the jibs is quite narrow. At this point the sail will still weathercock though, if I let the sheets go.

    (I have been sailing since I was a kid, but never competitive and don’t claim to be a good helmsman. When other people have sailed my boat (such as Alan Zebedee one day) I thought the boat went much better. Its not an ideal situation, my sail is home made and it was a first attempt. Sometimes the mains are not downhauled properly, the luffs a bit slack while the jib luffs are nice and straight, this is perhaps because of inaccuracy when making the sail. With SJR the jib luffs and main luffs need to match pretty well and I think I will do better next time. And I am not particularly skilled at sailing – I think the boat is potentially quite fast and close-winded, its a pretty good hull shape so I am surely not getting the best out of it. Its pretty good though and I am content with that. Thanks for taking an interest.)

    Thanks for answering my question, too. You have clarified that for me.

    PS here is something you might find interesting. Sailing flat down wind with the sail squared out, if I let the sail out more than 90 degrees there is a good chance the boat will roll quite hard in the direction away from the sail - ie a windward roll - and if not caught quickly the little boat can broach and roll the windward gunnel under. I am guessing that when the sail is paid out beyond 90 degrees it starts to become unstalled and begins to produce lift to "windward" even though running down wind. Its pretty impressive. Within a very narrow window, that sail can certainly pull hard.



    Last modified: 08 Dec 2019 13:20 | Anonymous member
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