Junk rig conversion of foldable rowing boat

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  • 04 May 2024 10:39
    Reply # 13352174 on 13291754

    Hi everybody !

    A few days ago I tested a new sail (origami SJR) for my foldable dinghy.

    The wind strength was 5 to 15 knots. By the end of the day the wind had increased to 15 knots and there were small waves on the lake. I prefer not to sail in stronger winds because the structure of my foldable dinghy is still too weak.

    The sail worked very nicely. Tacking, gybing, reefing – no problems. The swinging boards also worked very well. Following Graeme's advice - I raised them a bit and as a result the CLR moved a bit towards the stern (thank you Graeme).

    I made the sail as simple as possible. I did not sew the panels, I only used 45 mm wide double-sided adhesive tape.

    I placed string (or polypropylene tape) inside some of the edges of the panels. I don't expect to use this sail for a long time, I just wanted to see if the SJR sail would work well on my foldable dinghy.

    As you can see in the attached photos - all panels are the same, which makes them easier to make and use. To avoid using additional ropes and cutting battens, I used rigid batten parrels but different from d-formers. I called them "pistol parrels". They prevent the batten from moving forward. Each part in contact with the mast (including the relevant part of the batten) has a rolling element (parrel bead), which protects the delicate epoxy mast.

    I used a sail catcher similar to what Graeme used (a variant of the Slieve catcher). A simple catcher clasp can be made by cutting the catcher rod near where the mast slot in the catcher is. The two parts are joined by a sleeve glued to one of them, which allows the second catcher rod to slide out of the sleeve. This rod can then be lifted up to open the catcher. Details in the double photo.

    I noticed that the maximum camber in an origami sail is not at the point 1/3 of chord, but at 1/2 of chord, in the main part of the panel. I have the impression that this may reduce the sail's efficiency when sailing close to the wind.

    However, operating a junk sail is sensationally simple and easy. The only problem is the sheet - as it is long, it gets tangled in the cockpit, which can cause the sheet to jam. It also happens that sheetlets get caught on battens. I will probably have to use a longer boomkin at the stern and make a sheet box.

    Thank you to everyone, especially Arne, Slieve, Paul for their amazing ideas, and mainly Graeme for good advice and interesting ideas. I would also like to thank Kris for presenting his boat (Anna Lucia 2) on YouTube, thanks to which I learned about the existence of JRA and can benefit from your discoveries.

    (I prepared this text with the little help of our friend – Graeme. Graeme - beer is waiting for you ;) )

    4 files
    Last modified: 04 May 2024 15:06 | Anonymous member
  • 01 Jan 2024 22:18
    Reply # 13295775 on 13291754

    Thank you, for you too!

    Last modified: 01 Jan 2024 22:22 | Anonymous member
  • 01 Jan 2024 09:13
    Reply # 13295655 on 13291754
    Anonymous member (Administrator)

    That looks better. I can't imagine too much weather helm with that set-up. I think you would need close to 4m mast with that sail - still seems quite a lot for that little boat. Anyway, best of luck with it, I hope you can have some fun on the lake with your folding dinghy. Best wishes for the new year.

  • 30 Dec 2023 21:11
    Reply # 13295410 on 13291754

    Here is a drawing of my dinghy (simplified). The shape of the sail is not final.

    1 file
    Last modified: 30 Dec 2023 21:30 | Anonymous member
  • 28 Dec 2023 21:31
    Reply # 13294911 on 13291754

    Thanks Graeme for your reply.

    I read Slieve's article. Indeed, you are right, these are details that I can easily take care of later, when I have a new sail.

    The goal should not be to have a SJR - the goal should be to have a sail which has the right balance to suit your dinghy, with your fixed mast position (and current position of swinging boards).

    And you're right!

    The model I drew in the logo is actually a bit exaggerated. It represents my excessive expectations. Thanks for drawing my attention to this! Changing the proportions of the jibs in relation to the mains will not be a problem. Just trim the the jibs a bit and move them closer to the mast.

    I also realized that there is no point in exaggerating the number of panels. It may look nicer, but I must KISS !

    I can send the drawing of my boat (after completing it) even in .dxf format (I use LibreCAD). The point is that I have a number of other problems related to the weak construction of the boat, and the drawing will not show them.

    It is therefore possible that I will stop at testing the SJR on an existing boat, in order to use the experience gained to design (in the future) a slightly larger and more solid boat, but also a foldable one.

    I think that such a foldable boat would be useful not only for me. I would love to talk about it, but definitely not now because for now these are vague plans!

    Now I finally have to go to the garage and make (before spring) a relatively easy-to-use sail.

    Regards - Jan

    Last modified: 30 Dec 2023 22:27 | Anonymous member
  • 27 Dec 2023 22:48
    Reply # 13294669 on 13291754
    Anonymous member (Administrator)

    In reply to Kevin: There is also the Welsford Pathfinder dinghy Cirrus which is featured as Boat of the Month here (scroll down to March 2023) which features a SJR similar to (but not identical to) the Amiina rig.

    Jan might note that it is a 4-panel sail. It also has a proportionally larger upper panel. However, I would suggest to Jan, for a first sail, to follow exactly the proportions of the Amiina sail, leave off the bottom panel, and don't bother with the split in the top panel. That is, if he finally settles on a SJR.

    Jan: I really liked the idea of extending the swinging boards... With a new sail it may not be necessary. The current boards may be fine how they are - or (as in standard dinghy practice) it may be sufficient to adjust the angle of the swinging boards, with the lifting tackle. I would suggest leave that question for now...  don't change too many things at once.

    The sail catcher can be convenient, also when transporting by car, because the entire sail with battens is packed like in a case and it is easier to keep order. But doesn't such a large surface cause too much wind resistance? Certainly I find mine convenient to keep everything packed together for transport. You can use "hook and loop" tape at the top. to enable the sail catcher to become a closed bag, ie a sail cover, if you want. I have no idea if it "causes wind resistance", I would suggest that if so, it is a minor detail. In fact it is tidy and in line with the sail and may well disturb the airflow less than the exposed panels of a conventionally reefed junk sail. (I look at it as a lower extension of the sail).

    Spanned downhaul parrels… So a separate downhaul must be used for each panel? No, they are spanned, so that each one operates on two panels. You can refer to Slieve's notes. The relevant chapter is here.

    On the 5-panel Amiina sail, two of them is all you need. The only proviso with the spans is that you need enough space between the boom and the "deck" for when the span is in the reefed position. Slightly more than half the width of a panel is sufficient. I believe this need not be a problem with your set-up, but take care not to have the boom too low, as you need to allow enough room for the spans to fully extend.

    Also, provided you do not alter the proportions of the Amiina sail, you will find that no other control lines are necessary.

    If you use a 4-panel version of the Amiina sail you might be able to have a standing "downhaul" and short standing batten parrel on the boom (ie fixed, not needing any adjustment) as you would anyway, and just a single spanned parrel downhaul for the two battens above the boom. Perhaps the top batten and the yard could each just have a standing short batten parrel. That would give you the ability to reef one panel, or two panels, and would reduce everything to just one control line. I haven't tried it though. I find two control lines not too difficult to manage. They are left free when you hoist and just need a tweak when hoisted, tweaked again if you reef. A couple of cam cleats is all you need.  (If you change the shape of the sail or the "planform" then you may need additional parrels or hauling lines, you will have to find that out for yourself. That is why I would stress, stick to the exact proportions of the Amiina sail.)

    I would like to limit the number of lines as much as possible, as it can cause lines to become tangled in the trunk of the car and when preparing the boat for sailing. It's always a problem if you have to dismantle everything. I have my halyard, lifts and mainsheet block attached by quick release clips. (The halyard is unclipped from the yard and remains with the mast. The mainsheet block complete with mainsheet is laid neatly in the sail catcher, together with the sheetlets, nothing is un-roven). The parrel downhaul spans are also just clipped on to the actual downhaul ropes, so the parrels stay clipped onto the battens and go into the sail catcher, while the downhaul ropes ("control lines") stay with the boat. So the entire bundle (sitting tidily in the sail catcher complete with its downhaul spans, battens, sheetlets and mainsheet) are all stowed in the sail catcher free of tangles and ready to be re-deployed. The sail catcher is now a sail bag, with its bundle inside, with everything unclipped, and thus separated from the mast. For transport, it can be stowed in the boat or in the back of a car, without the risk of tangles. Clipping everything back on takes a little care, but it is still only a few minutes.

    ...soft rubber tubes in the place where the battens will rub against the mast...Metal battens on metal mast might need fendering, others can advise you on that.

    I'm also wondering how you attach the sail to the battens. For a simple little sail I have found wooden battens (split, one half each side of the sail, and screwed together through the sail) to be a quick and easy way, which does not require batten pockets or fendering against the mast. That is what you see in the photo of my boat. If you are only making a polytarp sail I would certainly recommend it. (For a better sail - well, that's a matter of opinion. I am trying batten pockets and aluminium battens this time round - already finding that it creates a great deal more work and for a little dinghy sail I doubt if batten pockets, metal battens and fenders, and hoops and loops are worth the trouble. Others might disagree. For a dinghy I would go back to split spars made from wood and screwed together through the sail - preferably some nice straight-grained spruce, though I have had to make do with pinus radiata which is not as strong and a bit heavy, but it still works. Rigging a dinghy is a slightly different proposition to rigging a larger sailboat. Split timber battens are quick and easy to assemble with a cordless drill-driver, and also easy to dismantle if you ever need to. Not everyone will agree with doing it that way.

    I just want to make a general comment. We are focusing here on many minor details and forgetting the big picture (one of my many faults). I think your first priority is to produce a scale drawing showing your proposed sail plan in relation to the lateral plane of the boat (with the boards in their normal position, and the rudder.) From analysing a photograph I felt that a 4-panel Amiina sail would fit your mast and probably bring the centre of area of the rig far enough forward to solve your problem and perhaps leave a little weather helm you could tune out with the centreboard.

    It looked pretty good to me, but only based on a photograph and not yet confirmed. Now, when I see your "avatar' showing your proposed sail, it looks to be much further forward (and too tall) - but without the swinging boards in the picture it is impossible to be sure if it is too far forward or not. Without a proper scale drawing, who can say?  Who knows: you might be better off with a slightly lower balance sail than 33% - if you over-do it then you will have lee helm, putting you in a worse position than you were before.

    So, before settling on the SJR and cutting cloth - and certainly before worrying about the minor details, make sure you have carefully considered the relationship of the centre of area of the proposed sail, in relation to the centre of area of the under-water profile of the hull (with the boards deployed in normal position) - preferably with a scale drawing. The centre of area of a Amiina sail will be near enough in the same vertical line as a vertical line through the midpoint of the boom.

    The goal should not be to have a SJR - the goal should be to have a sail which has the right balance to suit your dinghy, with your fixed mast position (and current position of swinging boards).

    [Edit: I scaled up your "avatar" drawing as it just doesn't look good to me. I noticed it is similar to, but different from Amiina's sail in a couple of respects.

    That's up to you, although I am sure if you contact Slieve he would be helpful and willing for you to use his design. Of more concern: your proposed sail appears (by eyeball) to have much more balance than 33%. I think you definitely need to re-consider that.]

    Last modified: 28 Dec 2023 00:55 | Anonymous member (Administrator)
  • 27 Dec 2023 21:31
    Reply # 13294662 on 13291754

    Thanks !
    A different laser, but also very interesting. Food for thought!

  • 27 Dec 2023 17:20
    Reply # 13294600 on 13291754
    Anonymous member (Administrator)

    A quick search for laser on the Knowledgebase produces an article in JRA magazine which featured a SJR laser and wayfarer in Magazine 79

  • 27 Dec 2023 13:46
    Reply # 13294533 on 13291754

    Thanks Graeme for your reply.

    Over the Christmas time, I thought about a few things:

    1) I really liked the idea of extending the swinging boards. It's so simple, but it should be effective! I had already thought about lifting the boards on a rope, recently I even prepared holes in the board edges, although I have not had time to mount the board halyards yet.

    If lifting of the existing boards doesn't help, I'll try to lengthen them, as you suggest.

    2) The sail catcher can be convenient, also when transporting by car, because the entire sail with battens is packed like in a case and it is easier to keep order. But doesn't such a large surface cause too much wind resistance?

    3) Spanned downhaul parrels… So a separate downhaul must be used for each panel ?

    Do you have any photos showing how these spanned downhaul parrels work?

    Do you also use other types of parrels?

    I would like to limit the number of lines as much as possible, as it can cause lines to become tangled in the trunk of the car and when preparing the boat for sailing.

    4) I'm also wondering how to secure the mast (epoxy-glass surf mast). The only thing that comes to my mind is some soft rubber tubes in the place where the battens will rub against the mast.

    5) I'm also wondering how you attach the sail to the battens. From your photos it appears that you do not use batten-pocket's but simply attach the panels to the tubes with a thin rope. This seems easier to me! However, do the tubes not slide out of such mounting?

    6) In the forum resources I found an interesting photo of the "Lores" laser (link) with a sail that is a variant of the SJR. Where can I find more information about it? (A search for "Lores" yields no results, and "laser" doesn't help much either).

    It's great that I can finally discuss various details about my boat with someone. I missed this :)

    Regards - Jan

    Last modified: 27 Dec 2023 17:07 | Anonymous member
  • 21 Dec 2023 12:24
    Reply # 13293367 on 13291754
    Anonymous member (Administrator)

    Jan: However, before Christmas there is some work to be done at home...

    Your priorities are right!

    I read about Tyvec that it makes noise. What is your opinion on this?

    I used it on the bottom  panel, for a while, as an experiment. I don't recall it being noisy. It is very soft, I would have thought the opposite. 

    As for the mast - I have already bought a second mast, 465 cm high from the bottom of the boat...

    I think the old mast was tall enough, and four panels is enough for that little boat. Just my opinion.

     ...the same drawing is in my logo, but I don't know why it is not displayed in the post header...

    It is displayed - have a look at the "Introduction" thread. It is there, but not very distinct. For some reason I don't understand, the photo that you put in the personal details section of your Profile is displayed in the post header of some forums (Introductory, for example) but not in others (the Technical forum, for example).

    However, if you put a photo in the "Current Boat's photo" section of your personal details, in your Profile -that photo will appear in the post header of the Technical forum.

    I'm also wondering how to plan the arrangement of sheets and sheetlets. 
    Everyone seems to have their own favourite way of doing it. I sheet the top two battens with one sheet, and the bottom three battens with the other sheet, so I have two mainsheets. I didn't know any better. It worked well for me so I never changed it,  but most people don't seem to do it that way. Maybe someone else can give you better advice.

    I noticed, that in “Serendipity” you have only one lazy-jack, or rather topping lift, is that enough?

    Serendipity has a pair of lifts at the mast (one each side) and another pair of lifts  near the aft end of the lower batten (boom) (one each side) [but not so far aft that the yard can get on the wrong side of it]. As far as lifts are concerned, I think that is normal. The forward pair is sometimes called "the mast lift" and the aft pair sometimes called "topping lifts".

    However, I don't have lazyjacks attached to the lifts, because I have a McGalliard-style sail catcher which does the job of muzzling the sail when it is lowered. This is not common, but for SJR it works better than lazyjacks, I find. You will find with SJR that the jibs don't seem to muzzle properly, they seem to escape the lazy jacks and flap around.  I found this annoying so I made a full sail catcher following Slieve's drawing, which cured the problem. The sail catcher has other advantages too, in my opinion, though only SJR rigged boats seem to use them. [It is possible that conventional batten parrels don't work conveniently with this sail catcher - that's the only reason I can think of why some people claim that this type of sail catcher doesn't work. This is speculation on my part. The system works extremely well with running parrel downhauls, I do know that].

    Sail catcher designed by Slieve McGalliard. The front fitting on mine (a U-bend which joins the two skeletal tubes at the front) fell apart, as you can see  - it is not needed anyway.

    I plan to use batten parrels in the form of tapes fastened with buckles

    I think spanned running downhaul parrels are best for McGalliard SJR, very simple and they work very well for that type of sail. Mine unclip, to enable the bundle to be quickly removed from the mast if necessary.

    Merry Christmas.

    Last modified: 23 Dec 2023 10:06 | Anonymous member (Administrator)
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