The mast balance of the JR

  • 09 Jul 2024 00:14
    Reply # 13379579 on 13379220
    Anonymous member (Administrator)

    There are some great photos of junks sailing down wind, but this was the one which first excited me about the junk rig. Mind you, any lug sail is superior to these other things,  in this particular situation. Not much of a photo but worth a second look - it's rather striking in its own way, is it not?

    I rather prefer the higher balance sails, in the single-sail category, at least for an inshore cruiser - but it's for particular reasons, and not a primary requirement.

    A couple of comments. Asmat (if I understood your comment correctly) considering that "split junk rig" seems to have become standard terminology for a particular type of junk rig, it might be better to refer to ketches, schooners, yawls etc as "divided" rigs (as they used to be called) rather than "split" - just to reduce the potential for mis-understanding. If that was what you meant. The other point which is worth repeating - Arne: as you know, 35% balance is theoretically possible and Slieve has "proved" it within the domain of model racing yachts. But considering the chances of spars bending or other unforeseen factors, including just plain miscalculation or measurement error, for anyone considering SJR, until someone brave enough has actually tried it, 35%  mast balance should be regarded as being on the brink of disaster in my opinion. While I would not go less than 33% for a SJR (otherwise what's the point?), I would also not go higher than a fairly carefully (and correctly) calculated 33% either. A runaway junk would be quite  a spectacle (from the shore!) and it has happened. Not trying to teach Arne anything, but for readers out there who might be thinking of this or reading about it for the first time....

    I agree the jury is still out on whether the somewhat specialised SJR has any measurable performance advantages over the other modern cambered rigs, but I do know it is very good if properly designed, and if some proper match racing could ever be organised, I would enjoy to place a modest bet on the SJR (but not too much!). If for some reason the high mast balance is required (either for personal preference, or to match some other requirements such as weight distribution or internal layout etc), the SJR does provide a valid choice. It may well be that Arne and Paul are on the right track too, as they continue to push that mast-balance/yard-angle boundary. That incremental type of development being discussed here is praiseworthy and very interesting I think.

    Last modified: 09 Jul 2024 00:38 | Anonymous member (Administrator)
  • 08 Jul 2024 18:24
    Reply # 13379401 on 13379220
    Anonymous member (Administrator)


    I am a little reluctant to go ahead with the SJR, now that my un-split sails work quite well. Only if I really needed to rig a sail with 33-35% mast balance, would I go SJR. Being strictly an amateur, I do what I like. It may well be that the SJR is better than my sails, but so far I have heard no proof that it is superior to windward, compared to the straight, cambered-panel JR.

    On the other hand, the broad, un-split JR, with little mast balance, soon becomes a handful to control downwind. This is why I these days aim to increase the mast balance, and thus make downwind steering easier  -  more like the SJR.


    PS: Here you can see a comparison between my Ingeborg and the Maxi 77, Ilvy . These are operational rigs in use, and not so extreme as the previous example.

    (Go to the new album Arne's sketches, Section 8 to see it in full size...)

  • 08 Jul 2024 14:02
    Reply # 13379276 on 13379220
    Anonymous wrote:

    Conclusion, so far:
    If these high-balance sails (up to 30%, so far) do not show any snags in handling or performance, I think I will advocate the use of them, in particular on sails above 30sqm. 

    So - the UNsplit junk rig?
  • 08 Jul 2024 10:35
    Message # 13379220
    Anonymous member (Administrator)

    How about increasing the mast balance?

    When I hoisted my first junk sail with barrel-cut camber in each panel on my Malena, no less than thirty years ago, I was quite worried that the mast would ruin the camber and performance on the port tack, so I kept the mast balance to a minimum, around 10-12%. Since it worked well for my use, I kept it like that. On my Johanna, a decade later, I was forced to haul the sail far aft to avoid lee helm, so her mast balance was set to the minimum possible (diagram below).

    Only when Paul Thomson rigged his La Chica with over 20% balance, did I start thinking. In the spring 2021 Ketil Greve constructed a 35 sqm JR for his Boudicca, this time with 60° yard angle, and rigged it with 21-22% mast balance.

    This very sail was copied this spring by Paul Schnabel, and he and his Toni now sail around with it set with about 25 % balance.
    That rig has turned their Maxi 77, Ilvy into a pocket rocket, even with an extra half a ton of cruising gear on board. Paul reports about great performance to windward. Moreover, he tells that they can also reef the sail when running downwind, without any need for downhauls. That surely would not work with my low-balance sails on Johanna or even Ingeborg.

    This new knowledge opens new possibilities. Below I let you see Johanna with the rig she used, and also Graham Cox’s boat, with a tentative large rig set with as much as 29% mast balance.
    Now, if such a high-balance JR turns out to work well on both tacks to windward, it would be a much better rig for offshore work, so there would be less need for splitting the rig into a ketch or schooner configuration.
    Look at the diagram of Johanna and Mehitabel running before towards you.

    • ·         With the CE of Mehitabel much closer to the mast (than on Johanna’s rig), the steering bias would be much reduced when running before.
    • ·         The sheeting forces would be reduced.
    • ·         Possibly the battens would see lighter load  -  until S-bending sets in at the mast...
    • ·         The centre of gravity (CG) of the sail would also be closer to the mast and this will result in less friction when hoisting or reefing the sail (..just as Paul S. reports...)
    • ·         With the rig sitting closer to the centreline, there will be much better ‘heeling clearance’ (37°) as well. I dipped the clew of Johanna’s sail quite frequently, and although this did not appear to cause any stress, it was still a bit annoying.

    Conclusion, so far:
    If these high-balance sails (up to 30%, so far) do not show any snags in handling or performance, I think I will advocate the use of them, in particular on sails above 30sqm. On smaller sails for lighter boats, I guess I will still suggest using the 70-degree yard and max 17% balance, as these sails lets one have a bit bigger sail area on a shorter mast. Weight counts more on smaller boats.

    Something to consider?

    (..go to my album, Anes's sketches Section 7-46/47 for full size diagram...)

    Last modified: 08 Jul 2024 10:57 | Anonymous member (Administrator)
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