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Anke and I are building our next boat, and writing about it at ABargeInTheMaking.blogspot.com. Access to the net comes and goes, so I'll be writing in fits and spurts.

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Fair winds!

Dave and Anke
triloboats swirl gmail daughter com

Tuesday, December 13, 2011

Why I Love Junk Rig

What, Me Worry?

Look at this guy! Hull looks fairly tender, weather looks woofy. The sail (absent a yard parrel) has fouled a stay. And there he stands, at ease and in control.

What better advertisement for Junk Rig (JR) could you ask?

JR looks complicated due to a lot of lines running every which way. But stress is dissipated wonderfully across the entire rig; JR sails were once made of woven grass mats! Masts are commonly free-standing and made of mere wood! In a day of high modulus ploycarbon sail cloth and rod stayed, aluminum alloy masts, this is barely conceivable. Yet the rig has been keeping the sea for thousands of years!

Quick Run-Through:

JR is a fully battened, standing lug (the sail is set on one side of the mast only) rig. A haulyard raises and lowers the lug*** and attached sail. Sheets haul and ease sail, but attach along the leech at the battens (rather than just the boom). This allows control of the shape of the leech, and avoids clew downhauls. Lazy jacks (a.k.a. topping lifts) control the fall of the sail, bundling battens and bunts as the sail is lowered. Downhauls get the sails down in all conditions.

***The JR lug is often called a yard, but suit yourself. Haullug just doesn't have the same ring, though.

So far, nothing too strange. But then parrels (lines which pass around the mast) keep the sail from blowing away from the mast on the lee side, and control the balance (center of effort) and set of the sail. Parrels are often running lines, giving great control over the sail.

Sails are usually flat cut. In the East, they're most often made of rope-edged cotton, which stretches (cambering the sails) and curls the leech back (so called gurney flaps).

Now, despite anecdotal evidence from the East where working Junks with tired sails have been observed to smoke Western racer cruisers, JR has a bad rep. Here are a few reasons why...

Col. Blondie Hassler did much to popularize JR in the West. His book Practical Junk Rig is masterful, and is still considered by many to be the 'bible' of JR. He proposed a standard sailform based on parallel battens, topped by a triangular fan. This handles reliably, without requiring hands-on intervention; perfect for short-handed cruising. But in China, parallel types are primarily used on riverine Junks, running upriver against current, and supplementing current on the way down. Ocean going Junks tend to sport fanned sailforms; better performance but more work. Most JRs you will see in the West are based on the less efficient riverine sailform.

We, in Western adaptations, are just recently starting to learn to shape the panels between battens and simulate gurney flaps in our low-stretch materials. Not surprisingly, we're picking up speed and windward ability.

Where else might aerodynamic lift come from? Vincent Reddish pointed out that horizontal airflow over canted battens (especially fanned, ocean-going sailforms), allowed to twist in the manner of JRs, describes an airfoil. Westerners, accustomed to shaped sails, try to minimize twist. With full leech control, it can be almost eliminated, all the time - so we do (see Hassler's geometries). Flat-cut sails, sheeted flat are planks. Oooh. JRs can't get to windward! But let 'em twist and you've got variable draft control; deep camber for light winds, flatter for high winds. As we learn to sail them, we're again picking up speed and windward ability.

So what do we do? Anke and I dumb ours down, of course.

Parallel battens for easy handling. Sheet and haulyard are the only running lines, all others are standing. Multiple sails allow us to adjust sail balance without extra control lines. Continuous running sheets (5 and 6 part) are simple haul / ease, and mechanically advantageous to handle (no expensive winches), but lose fine control of leech shape. Substantial battens drop the sails without downhauls (do have to round up, a bit, to drop sail in high gale conditions, with sail between wind and mast). We thus keep line handling to a bare minimum. Parallelogram sails behave very well (sheets clear with no fouling), but are not efficient by Reddish hypothesis. Sails are low-stretch and flat cut (what did I just say about that???), but only 'cuz we were in a hurry to go sailing.

A word on our unusual upper panel shape... it's essentially a Polynesian Crab Claw. When deep reefed, it retains great shape and drive. The deep hollow leech brings the CE inboard for reduced weather helm (I think it could be considerably deeper... I'll talk about that another time). It was an experiment that worked out.

Summary of JR advantages:

  • Inexpensive to build and maintain (simple components, DIY sails).
  • Robust (distributed stresses reduce likelihood of gear failure).
  • Light booms reduce danger of concussion. 
  • Sails entirely handled from the cockpit via sheet and haulyard.
  • Quick reefing (Let go haulyard! BAM, BAM, BAM! Make fast! Trim Sheets! Done in 5 to 10 seconds!)
  • No tack or clew downhauls; no reef nettles (no lurching about, wrestling bunts, tying nettles overhead).
  • Jibes all standing with no problem.
  • Sail flogs very little (tamed by battens in all weather... easier on sail and nerves).
  • Can reef upward (raising booms for deck loads, tarps, etc.).
  • Lightly stayed, if at all (cheap, low windage, little to no 'shrieking rigging').
  • May spread more area (easy to handle, so 10+% more; quad sails spread wide and low).
  • Few to no sail changes (all area in working set).
  • Can climb battens like ratlines.
  • Can set masts free-standing, in tabernacles (for easy dropping / maintenance).

Y'know... I'm not a fanatic. Other rigs have advantages and allure. But as a cruising rig for wild waters and a shoestring boat - the only kind I'll likely ever own - junk rig keeps wooing me back.


Whuddaya know? It DOES get to windward!  -- Photo Courtesy Tom Krantz

1 comment:

  1. The 'Gurney Flaps' (GFs) I mention turn out to be a longer, more complicated story than I knew at the time of this writing.

    Controversy in a nutshell:

    JR gurney flaps are misnomers, bearing little resemblance to the real ones found useful in automobile design and trialed in aircraft wing design. They are much more like the drag flaps used to slow aircraft on landing.

    Proponents claim that they enhance (windward) performance, with various explanations as to why. Opponents argue that they induce drag (aerodynamically correct), so should not be used.

    JR GFs set aft of a sail's leech, in line with the sheets.

    Close-hauled they are nearly, but not quite in line with the sail's airfoil, causing drag (undesirable, on the wind).

    As the sheets are eased, their - and the GF's - angle to the sail increases toward 90deg, producing ever more drag (desirable well off the wind).

    I've seen a video (which, unfortunately, I cannot locate) in which a traditional Chinese junk was distinctly fitted with a JRGF.

    My hypothesis is that a trade-wind vessel might choose a JRGF, sacrificing occasional windward performance for enhanced downwind performance.

    Be aware that the benefits, if any, are hotly contested.

    Dave Z

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