The Top 50 Advantages of Junk Rig

Discussion in 'Boat Design' started by David Tyler, Jan 16, 2014.

  1. bpw
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    bpw Senior Member

    So if I did my math right your spar should be about 172 lbs for the bare tube, not bad. I will need to check if something similar would be strong enough for our new boat. Our righting moments my be quite a bit higher than your boat.

    Two masts (or a headsail)would be needed for us, I would not feel comfortable sailing into a tight spot without the ability to back a jib or foresail to help control the bow. And I would be looking for 700 plus square feet of sail.

    It is good talking to someone with a good bit of first hand experience with the junk since I am quite interested in it. Thanks for putting up with getting poked and prodded.

    I think my ideal would be something similar to what Eric Sponberg did for Capernicus, a freestanding single masted fractional rig. Most of the advantages of a freestanding rig, while retaining a headsail for manuverbility. Maybe carry running backs to allow some control of mast bend and headstay tension. Requires a tall mast though, so the weight might be tough to keep under control without carbon. Maybe with a full batten main it would be OK since I could shorten the mast and still retain sail area.

    Can capernicus set a spinnaker?
     
  2. Stumble
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    Stumble Senior Member

    Edit: deleted: Eric Sponberg did a much better job than I did covering the same information.

    In addition I would love to see the effect of pulling a unstayed mast off and going to a junk on the same hull. If anyone has this information I would be very interested.
     
  3. bpw
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    bpw Senior Member

    Thank you so much, was having a really hard time finding actual numbers for spar weights on smaller free-standing rigs.
     
  4. David Tyler
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    David Tyler J. R. A. Committee Member

    bpw, I suggest you take this into account:
    If you put a "normal" bermudan mainsail, with a headsail, onto an unstayed mast, the mast must be much higher, and much stiffer (to maintain leech tension and forestay tension) than a mast for junk rig. This means that the mast is much heavier and much more expensive. I was once moored alongside a Wylie of similar size, and his mast was HUGE, compared to mine.

    In contrast, two masts each carrying a 350 sq ft junk sail would be relatively light, low, small in diameter and inexpensive. I'm in favour of making two equal sails, for the very pragmatic reasons that making two of everything is easier, carrying spare battens is easier, sailing goose-winged is easier.

    If you're really wanting to aim at the high performance end of the unstayed rig scene, may I throw this over to you? Tystie has had a single-masted junk rig for half of her sailing, 40,000 miles. For the other half, she had a ketch rig with soft wing-sails, very much based on junk rig, with chinese sheeting to stiff battens, but with articulating battens designed in the way that Tom Speer has described for designing a wing mast/ sail combination. I'll attach a cross sectional drawing. I used Wortmann fx77w153 section as the basis. This takes more work to make and assemble, but the performance is better than a pure junk rig. While it won't ever match the performance of a hard wing mast, because the soft sail is rougher and not held to a precise shape, when I've tested it by holding up a ribbon on the end of a long stick, the airflow was behaving very well around the luff and lee side. I'd rather like to go back to this rig, as it was actually even easier to handle than pure junk rig, on top of the performance advantage. Maybe next time, I'd like to try using UI1720 section as the basis of the design ( the section designed at the University of Illinois for use on double skinned hang gliders, so appropriate for building with a fabric cover). The articulating mechanism needs to be different, but I'm working on a solution to that.
     

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    Last edited: Jan 19, 2014
  5. David Tyler
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    David Tyler J. R. A. Committee Member

    Stumble,
    I don't quite understand what you're saying. There have been plenty of conversions from bermudan to junk, on production hulls, and there are also a good number of conversions of the early Freedom cat ketch boats to junk. As a result, there are a lot of much happier boat owners.
     
  6. David Tyler
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    David Tyler J. R. A. Committee Member

    That's the way it goes. There are always plenty of folks ready to say "I've never tried it; therefore, I'm sure I won't like it".
     
  7. Stumble
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    Stumble Senior Member

    Have there ever been any one design racing against a slop and a Junk rig? I don't see a proponent of Junk rigs (ie someone willing to make the switch) as a good neutral party.

    If not, I would be interested in seeing if we couldn't get two boats one of each type on a race course together and see what happens.
     
  8. David Tyler
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    David Tyler J. R. A. Committee Member

    Oh, if only this could be brought about, many people would be delighted! Unfortunately, folks are only too happy to talk about it, but when it comes to the point, not so happy to actually do anything about it. When I owned a class boat (a Sadler 25), I tried to get a fellow member of the sailing club I was in, with an identical boat, to come out and play. He would only mumble something about not really being interested in performance. Other than that, I can only report some good performances in big-fleet races, like the Round The Island Race. All I can say for sure is that a good number of experienced sailors have converted their boats from bermudan to (modern, cambered panel) junk, and have then reported anecdotally that they were sailing just as well as they ever did, but more pleasantly.
     
  9. bpw
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    bpw Senior Member

    Lets ignore headsails for a bit, that was an uneeded tangent on my part. Once we are talking no headsail rigs it seems the spar will have to be about the same no matter what sail you put on it. Maybe a touch taller with a Marconi size sail but with full battens probably not a whole lot. Given how bendy the tops of most modern frac rigs are I doubt leach tension will be an issue. If a Wylie has a much bigger mast than yours I would guess it is a result of higher righting moment, not the sail shape.

    Do you carry any light air sails on your current junk rig?

    You have my attention with the wing sail...I have never paid much attention to them before, thinking they would be too delicate/finicky for cruising use. I would like to hear more.

    Why did you switch back to a standard Junk rig?

    What should I be googling to get more info on that set up and ways of designing and building? I will be looking up Tom Speer, is info available on the JRA site?

    Perhaps starting another thread would be a good idea?
     
  10. pdwiley
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    pdwiley Senior Member

    There's a writeup in one of Tom Colvin's books about doing this on one of his sharpie hulls. 'Offshore and Coastwise Cruising Wrinkles' I think.

    Can't remember the details ATM but IIRC he compared a junk rig to a marconi rig and a gaff rig. Marconi was better upwind but the gaff & junk rig walked away going downwind. No giant headsails on the marconi rig though.

    I've said this before and I'll say it again. If you have a budget of say $10,000 for your 850 sq ft sail area rig (spars, standing & running rigging, sails, winches et al), a 12m 7.5 tonne displacement hull and want to go sailing, I'll bet that you can get a lot further, a lot faster in a junk rig than a marconi rig.

    Mainly because I very strongly doubt that you can *build* a marconi rig for that price, so you won't be going anywhere....

    You have to buy all new materials but you can make anything within your ability to make. I say this because someone will come up with a once in a lifetime bargain on an unobtanium spar or brand new sails which is useless as a datum point, because nobody else can do the same. With all new materials, anyone can duplicate a documented set of expenditure.

    Friends of mine are in the final stages of building a marconi cutter rig on a 12m hull. So far their documented expenditure on rig & sails is 5 times the amount I've specified..... and the boat isn't in the water yet.

    PDW
     
  11. Petros
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    Petros Senior Member

    it seems to me it would be an interesting experiment to take a Lazar, which already has a free standing cat rig, and fit one with a junk of the same surface area, than race it together with conventional Lazar riged boats, and see how they perform. a sail that small would not cost too much, it can even be made from Tyvek so something similar and inexpensive.

    I am a big fan of the junk rig, I think it can be greatly improved with some further modifications, in addition to the cambered panels and the two surface forward sections. I have built some small ones for dinghys, with a more elliptical plan form, and found it outperformed similar sized boats with conventional or lug rigs. but my experiments were not optimized, just tinkering with plastic tarps and duct tape.

    I want to incorporate some of my ideas into a modified junk rig for a 16 ft pocket cruiser I hope to build one day.
     
  12. David Tyler
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    David Tyler J. R. A. Committee Member

    Not quite true. The yard of a junk rig extends the sail above the mast, so the mast is shorter than for a bermudan sail (or a wing-sail) of the same area.

    No light weather sails, just an iron topsail. A Beta Marine 20HP diesel goes to windward pretty well in 5 knots of wind, and a junk rig goes downwind pretty well in 5 knots of wind.

    Why did I switch back to junk rig? I'd designed a fanned planform junk rig at 317.5 sq ft for my friend Annie Hill in NZ, who lives on a Raven 26. It turned out very well. I'm a designer, and I can't stop tinkering about to see whether I can make something better than it was before. I wanted to see what was the practical limit of size for this shape of sail - I'm pretty much at the maximum.

    I did get some interest from some proa enthusiasts concerning my wing-sail rig, so I started up a new forum for that, on the JRA website. I described all the features of my rig there, but I have to say that it's not necessarily how I would do things now, having gained some experience in using CFRP to make my current spars. It's a members only forum, so you'd have to join, but it's only 7GBP a year.

    I agree, if we have enough interest in soft wing sails going here, a new thread should be started. I have one JRA member very interested, for the 40ft boat he's just bought that will need two sails of 500 sq ft each, and another JRA member in NZ who is thinking about a 20ft fast fun-boat with this rig, so maybe it's time to get down to some serious design work. I'll just attach a .dxf file of where I am at the moment.
     

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  13. bpw
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    bpw Senior Member

    Ok, so I may have done the math wrong, but assuming a righting moment of 25,000 ft/lbs and a 40 foot mast including bury. (I am guessing RM based on a slightly similar boat.)

    it looks like Would need a 12 inch diameter at deck tapering to 4 inch mast with a .25 wall to have a 3 to 1 factor of safety (what Eric Sponberg recommends in his writing).

    That leads to bare tube weight of 286 lbs.

    Heavy, especially if I need two, but maybe I am doing theses calcs wrong. Though given the Weights of the carbon fiber sparhawk masts it seems like it could be in the ballpark.

    A 16 inch diameter tapering to 4 inches would allow .125 in wall and a weight of 182 lbs, a lot better but that is a seriously fat mast.

    If any of the actual engineers want to tell me I am completely confused I would appreciate it....
     
  14. bpw
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    bpw Senior Member

    David Tyler, your mast dimensions seem a lot smaller than what I am getting, do you know the RM for your boat of the safety factors you designed to when making your spar.

    Or was it done to the Blondie Hasler rules of thumb based on sail area?
     

  15. David Tyler
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    David Tyler J. R. A. Committee Member

    Yes, it would. The JRA was actually given a Laser as a starting point for this, but do you think we could get anyone to get off their rear ends and make this happen? No, we could not.

    But anyway, a planing dinghy is not necessarily the best platform, for realistic results that could be applied to larger boats. A 16 - 20ft displacement dayboat would be better.
     
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