Junk rig on modern hulls

Discussion in 'Sailboats' started by BATAAN, Sep 2, 2011.

  1. BATAAN
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    BATAAN Senior Member

    More research material from China as applied to a western vessel. Here's a couple of Swatow "Big Eye Chickens" contrasted with a leeboard river junk with tall narrow sails to catch wind over levees and riverside trees. Also a smaller, non-BEC, ocean trading junk to show what level of finish and technology is actually required by the ocean, given competent seamen. Davy Jones doesn't care a fig about sandpaper or varnish, but he's big on watertight compartments and stout spars.
    Notice the size of the hoisted rudder on the anchored junk, and also how the geometry of the sail puts the yard far behind the mast when lowered. Look at the hoisted sails on the other BEC and how they have a long vertical luff and the main yard sticks far above the masthead like a sliding gunter, and from there the leech is as heavily roached as possible to gain sail area. BEC seems to have the largest possible sail area on the shortest possible mast.
    As you can see by the size of men next to it, the mast on the anchored BEC is at least 20" in diameter to handle the brute force of the huge sail, even with shrouds. It also is thicker athwartships by added "fishes" seen in the stern view of the same ship.
    All those battens and the yard and wet sailcloth adds up to tons of mass in a hard rain, combined with a lumpy sea and a stiff flat midsection translates into slamming inertia loads aloft that break things, so the huge "built" mast with lots of iron bands, probably original to this 100 year old ship in the pic.
    When translating this crude but mature industrial technology into some sort of sophisticated yacht use on an experimental vessel with no cargo capacity other than a six-pack and a credit card, great care should be taken to avoid pitfalls due to inadequate stability, and strength must come from expensive engineering and fabrication instead of stout, thick, and heavy timber. Colvin's designs are as close as anyone's come I think to a workable concept. His steel and aluminum junk adaptations work well. GAZELLE is something different and seems to depend on the owner. A couple who own one on Lopez Island have had it 20 years and cruised Mexico a lot and are planning a South Pacific trip soon. They love the boat.
    BERTIE's hull is an old industry standard for a couple hundred years and her gaff sloop original design rig was adapted by replacing the gaff sail with a BEC Chinese type, which required a bit taller mast and different design aloft, but the weight is about the same as a big gaff main, long topmast with its rigging and large topsail would be, but much much easier for a small crew to deal with.
    Other than the mainsail, BERTIE's rig is conventional to the point of boredom. Stays go through bowsprit so headsails come all the way down, lashings instead of turnbuckles, English south coast beach boat standing lug mizzen on running bumkin.
    Here she is under sail, bending on the main, with 4 reefs in, and with the watersail set.
     

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  2. TDSoren
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    TDSoren Junior Member

    Not just stretchy

    Here is a link with pictures of "shaped" chinese sails. Don't care for it myself as I think it makes little difference.
    The blue sail in photo here just looks stretchy, not shaped.


    This is quoted from a previous post. Not sure how to put it in the Box thingy and do it right.....

    Actually, the sail isn't stretched, it has an intentional 8% to 10% camber built into each panel. That Boat belongs to Arnie the Norwegian, considered by the folks over on the Yahoo junk rig forum to be the guru of the modern junk rig. Arnie used to do flat sails, but found that going cambered made the boat go MUCH better to windward. the only drawback is now "Hong Kong parrels" are required for diagonal stability in each panel. these are fixed and never adjusted, so they cause no addtional work in operating the rig.

    Go to the Yahoo forum and to the Junk rig association page, and you'll find that cambering the panels has been the single biggest advancement since hasler, colvin and van loan.

    It turns out that when we westerners "tidied up" those sloppy, baggy chinese sails with our modern materials, we removed a vital component of the design. The airfoil.

    I just built a 78ft2 junk to replace the 65fts marconi on my 10' marples trimaran, and it works GREAT! I'm sure I can point a little higher with the marconi, but the reaching, running and easy reefability more than compensates for a few degrees lost pinching it up.

    Tom
     
  3. BATAAN
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    BATAAN Senior Member

    On BERTIE I have found that the adjustable luff parrals, when slacked, give a baggy and somewhat loose cloth which I use in light air, and when tensioned, pull the battens aft and spread them due to the Swatow geometry, flattening the sail when it breezes up. Thus we have a good bit of control over sail shape and it's not all flat panel. In a gale at sea, I would not care for loose cloth that flaps in a 50 knot wind and cannot be flattened. Been there too many times.
     
  4. TDSoren
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    TDSoren Junior Member

    Baggy Cloth And High Wind

    I would imagine in 50kt winds the sail would be reefed down to the diagonal panels at the top. these are usually cut flat or very nearly flat, the camber only being built into the rectangular/parallelogram panels below.

    The other thing that attacts me to the camber method is the ability to choose battens as stiff as possible without getting too heavy. It's my understanding with flat panel sails you have to fine tune the amount of bend in the parrels to get the right balance between sail shape in various wind strengths. This might be what leads to breakage problems for some people.

    As to putting in the camber, Arnie's sail in the phot has a very simple method called the "barrel cut" ariived at by simple curves in the top and botom edges. very sophisiticated air foil shapes can be achieved by the "shelf cut" method where there are horizontal sections of cloth shaped liked the ribs of an aircraft wing. Apparently these are much harder to sew for amateur sail makers.

    http://www.junkrigassociation.org/R...'s files/20091119 Camber, the Johanna way.pdf

    I used the barrel cut on my sail, and it came out surprisingly good for the first thing I ever sewed other than holes in my jeans. The only real mistake I made was using the very heavy white tarp in such a small sail. I did it in the interest of strength, but a much lighter material would take a better curve sooner in lighter wind when it's most important.

    Tom
     
  5. BATAAN
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    BATAAN Senior Member

    Interesting ideas and development direction. Thanks for explaining. Barrel cut is like cutting any 4-sided sail, you usually build a varying curve into the luff, leech, head and foot, only here it's only the head and foot of each panel. I supposed a concave curve on the luff and leech might help a fluttering problem if it develops.
     
  6. TDSoren
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    TDSoren Junior Member

    Gary Dierking played with almost the exact same sail i built on his Wa'apa outrigger canoe. he wanted the reefability as well for varying wind strength. he progressed from flat cut to 5% camber with guerney flap to more camber without guerney flap.

    He also found that the camber made the sail much more close winded.

    Google will find his blog where he talks about it.

    I went this direction because on my Tri you sit in a formula 1 race car style cockpit with foot operated rudder pedals. Going "on deck" is a major pain in the a**. The 65ft2 marconi has a luff sleave, and was a major pain to take in the single reef it did have. There's a spinnaker as well, but this got REALLY complicated. I can now vary sail area in seconds from the cockpit. I went from a 19' mast to a 13' mast with more area and no sail twist when running.

    In this small tri the beam/WL ratio isn't fine enough to bring the apparent wind forward like most multihulls, so windward performance wasn't as critical as ease of reefing and doing away with the spinnaker.

    It is SO MUCH FUN sailing by Portland yacht club in a multihull with a junk sail and watch all of the traditionalists scratch there head on how I beat so well up the narrow channel.

    Tom
     
  7. BATAAN
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    BATAAN Senior Member

    That sounds like a very fun boat. Keep sailing!
     
  8. BATAAN
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    BATAAN Senior Member

    Here's an interesting photo. Couldn't find anything else but obviously somewhere there are at least 2 junks with battened jibs.
    Comments?
     

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  9. TDSoren
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    TDSoren Junior Member

    Very cool. looks like they've still got parrels on battens going around a shroud versus a mast.

    I've had ideas of using a bipod mast on a cat and running the parrels around either a very thin rod in tension or maybe a heavy cable or rope. Not so much to reduce the effect of the mast on one tack as for structural simplicity. Might be a side benefit of better airflow over the sail compensating for the higher total mast drag on the boat.

    Tom
     
  10. MastMonkey
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    MastMonkey Junior Member

    Any clue what the parallel lines are that run vertically down the middle of the main sail? The luff is surprisingly round on the jibs, or is that more of an illusion?
     
  11. BATAAN
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    BATAAN Senior Member

    The photo is of the "off" side of the sail. The battens are on the other side against the mast of course.
    The vertical ridges are I think from strain reduction ropes which take the weight of the battens instead of hanging it on the cloth. For cheap cotton sails this is a good idea, but make the ridges you see. The sails are loose and stretchy enough that this really shows up. It's a common thing on some junk sails. Not necessary with stronger sailcloth and full leech roping. There may be other reasons the Chinese do this, but I am not aware of them. I have never seen a photo where these ropes are adjustable, just fastened to the battens to pick up the weight of the sail. The strain on the cloth of the upper panels when hoisted fully and wet is considerable, and these lines are I think to keep the sail panels from tearing, and so only wind loads are involved, not the considerable weight.
     
  12. rayman
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    rayman Senior Member

    Bataan, have you read Brian Platt's book of his voyages in "High Tea" she had standing rigging on all three masts and what looks like running backstays on the mainmast. Do you think that is feasable?I have recently bought a little 20ft cruiser/racer and like the idea of copying "Ming Ming's" rig but using my existing mast and permanent shrouds, (forestay and one fixed per side.) regards ray
     
  13. BATAAN
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    BATAAN Senior Member

    Haven't read "High Tea", but will look for it. Chinese lug works with shrouds if the yard is very high peaked and little overlap, basically replacing a gaff sail. The yard tends to get around the wrong side of the mast like this so a second yard parral is rigged to keep it behaving. Putting CL on a Marconi mast is a little more complex. Check out BERTIE's photos for standing rig example as well as clearances. We have running backs but only use them in rough conditions to take the whip out of the mast. Shroud upper ends must be as far up the mast as possible to give clearance, and yard should be a good bit below them.
     
  14. rayman
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    rayman Senior Member

    Peter, here some pics of "High Tea" built and sailed across the pacific in early 50's, was still in existence in 2001 in a yard in New Jersey wherever that is. His book is "Parallel 40North to Eureka"


    And a couple of "MingMing" now with permanent bowsprit.
     

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  15. joss
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    joss New Member

    saugeen witch & gazelle

    First post so please bear with me. Owned 26' saugeen witch JULIA 20y. and now have aluminum gazelle 8 y. Tom Colvin tested a marconi, gaff and junk rig on 3 identical steel sharpy types with a fin keel. The marconi was slightly better to windward, but the junk and gaff were second/third if memory serves and not enough shabby to warrent the other compromises attendant to the rig. All other points of sale the junk showed superiority probably because it is able to carry more sale longer and is easier to reef. Gazelle is a semi-modern hull: full keel with cut-a-way forefoot, narrow beam, light displacement. Weight is speed and the only resistance to flow is drag. Overweighting the fine hull of the Gazelle is a routine abomination that is easily cured. Tom has related that windward performance of many he has personally "tweaked" involved shifting wight (heavy deep/out of the ends) and usually adding a fair bit more weight slightly forward to get her to keep her bite. McCloud and Hasler used even more "modern" hulls to good effect. I am open to being wrong, but windward ability is a function of luff according to some noted navel architects. Gazelle has it in abundance even if it is split. As noted, the shoal draft leaves the windward performance to be less than stellar. But, after almost 2 years in the Bahamas it has shown value for the compromise. The theory of sail drive from a junk follows a name that I can never remember, but remember it being in an article in the NY Times/Science Times about the aerodynamics of the Wright brothers craft and is related to thin foil aerodynamics and not the NASA foil "modern" rigs strive to emulate. Because laminar flow is an illusion in our regards, a more 'natural' way may have been to emulate the controlled turbulent flow seen in the way most simple life forms generate force to defy gravity and sail. The jib on gazelle has been set by some users as 'jig and jigger' for going to windward more comfortably when sea conditons allow. The widow maker is not for the weak or timid when it starts to dance.
     
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