

Junk Sail Tutorial
Y2K is mainly gone and here are some illustrations - at long last - of various authors' geometries. More coming.


A junk, probably photographed in the 1870s or so, with bamboo-matting sails, and an array of assorted canvas kites. The mat sails are the original form of Chinese junk rig. Later cotton became common, and today boaters use Dacron, cotton, or polytarp.

Photo courtesy Mark Anderson and his mighty stereopticon.

Sail Geometries
A Traditional Junk Sail by Vincent Reddish
Junk Rig Shapes
These sketches show different approaches to shaping the sail. I was working on showing them all to the same scale so the size and shape could be directly compared, but have not had time to play with my CAD program.

See also my page about sampans: Cranks With Planks

Van Loan
Yang Tse Pelican
Traditional: Vietnamese
Bolger Gaffer
Tiny Junk Sail on a 12-ft Peero
The Rigging
The Sheeting

Different Sail Geometries

Everyone who writes about junk rigs seems to have a favorite sail geometry. Blondie Hasler's may be the best-known and most-used because of his book (Practical Junk Rig, by Hasler and MacLeod) and its following in the UK. Tom Colvin and Derek Van Loan are the two best-known American junk-rig champions.

Traditional Chinese rig geometries varied widely but two sources covering them are G.R.G. Worcester's Junks and Sampans of the Yangtse and the section on "Nautics" from Joseph Needham's immense Science and Civilization in China. Vincent Reddish analyzed photos in several books in order to come up with his formula for a traditional South China sail. Tom Colvin's preferred sail shape is much the same as Reddish's. Reddish has provided a very simple "cookbook" approach to making the proper sized sail.


Vincent Reddish: South China Junk Sail

Reddish decided that the Chinese must have used simple proportions to lay out a sail, perhaps employing a rope which they could fold into different lengths. He compared photos of seagoing junk sails to get the following relations. He settled on the boom as the unit and all other measurements are fractions of the boom length.

Vietnamese and Thai balanced lug sails are shaped similarly in many cases.

Reddish used two bamboo poles for each batten, lashed (taped, actually) together in the middle. The skinny ends of the poles met in the middle of the sail while the larger ends were at luff and leech. His yard and boom were of pine. He described two sails. The larger one had a 17-ft boom.


His approach is nice and cheap. His sails were made from polytarp, the battens were bamboo and the yard and boom were pine. Boltropes were polyester.


Laying Out the Sail

So the only dimension needed is the desired boom length. Ten units is a good sample length; we'll use feet. That way, you can simply use these numbers as percentages. (Think of the Yard length; divide it by 10; 6.67 ft becomes 0.667 or 66%).

You can think of the center of effort as lying above a point halfway along the boom. Reddish also says that "only 8%" of the sail area is typically in front of the mast. This would mean something a little over one foot of our 10-ft boom ahead of the mast: 7ft x 1.5ft is 10.5 sq ft so the boom must cross at about 15 inches.



10 ft

Sail Area:


111 sq ft    (Aspect ratio is about 1.1)




6.67 ft

(66% of Boom)

70 deg angle to Luff

Yard Offset

2.25 ft

Distance from peak of Yard to the Luff perpendicular



10 ft

   45 deg (approx)



   30 deg    "



   20 deg    "



   10 deg    "



   05 deg    "


10 ft

   < 5 deg


Luff Overall:

6.67 ft

Each Panel

1.11 ft

  Each Panel's Luff



6.67 ft

   Panel 6
   (Attached to Yard)

Upper Roach


5 ft

   Panel 6 (Yard Peak to
   the end of Batten 5)

Leech "L"


3.33 ft

(50% of Yard)

   Batten 4 - 5
   Panel 5

Leech Dimension for Panel:

2.9 ft

   Batten 3 - 4

2.5 ft

   Batten 2 - 3

2.0 ft

   Batten 1 - 2

1.67 ft

   Panel 1
   (Boom Panel)

This information is from Practical Boat Owner 1/92, "Junk Rig Decoded". Many thanks to Peter Berrie for sending me a copy of the article.

Making the Sail

Spars are laid on the ground and staked in position. A rope (heavy grey line) forms a framework along the luff and leech and along the boom and yard. Reddish used 5mm polyester rope (about 3/16"). This frame of rope is interesting, because it allows a very taut luff without depending on the sailcloth to hold the tension. It also spreads the stresses on the leech directly to the battens.

The sail itself was made of a single polytarp cut to the proper shape and "hemmed with a thinner rope" (1/8" polyester would work; so would nylon or polyester webbing).

He is not specific about lacings other than to say that the sail was then "stretched tight" and laced to the framework and the battens. I imagine this means sewing loops around the light hem rope and the boltropes with heavy sail twine.


Worcester depicts a double-roping system used on the large sails, and if I can find the material I will add a scan of his diagram. It doesn't seem to be strictly necessary, but it would certainly add strength. This traditional approach includes a head batten laced to the sail. The head batten is then tied to the yard. From what I've read, I suspect this is because the yard was rarely removed from a vessel; the head batten is a surrogate yard which is used when laying out and constructing the sail.

COD & Bob Cavenagh construct a 160 sq ft sail, per Reddish, in about 4 hours.

That's Bob doing quality control on the luff.


Sail on Bob's canoe yawl. The boom is swung toward the camera and is longer than it looks. It did work, though we had almost no wind, and not enough time to work out all the sheetlet lengths to our complete satisfaction.


Reddish also says that he picked batten sizes which would give him about a 10% camber in normal sailing conditions. On our 10-foot sail, the battens would bend so that they were about 1 foot out of line near the middle of the sail. (Make sure the boom is stiff enough that it does not bend, however). Photos of traditional Chinese sails show some bending, especially when sailing to windward.

Finally Reddish says he made each panel somewhat baggy simply by pushing it down in the middle as he attached the battens. The corners wrinkled some, he says, but that did not seem to cause any problems.

Update: 1998

This note comes from Bill Samson in Scotland. As it turns out, he was a student of Dr. Reddish some years back and was able to get an update for us. The main differences seem to be returning to rigid battens and adding some darts to the leech to give the panels a little shape.

Dear Craig,

I had a long telephone conversation with Vincent Reddish this evening.

I asked him how he fixed the battens to the sail and he said he didn't - the sail is fixed to the battens! The sail is sewed on, with whipping twine, to the yard, boom and bolt-ropes. The battens are double - bamboo on each side of the sail. He puts a stitch in every six inches or so, using burgee cord, so that the sail is sandwiched between the battens.

He uses a 360 square foot polytarp sail, made in this way, on his Laurent Giles designed VERTUE cruiser. His original experiments were with a Laser-17. He was at pains to point out that his sail is quite different from Hasler/Macleod, being based directly on those found in Chinese boats.

His main reservation about polytarp is its lack of stretch compared with the Chinese material, so he has put in a little broadseaming along the leach - at each batten. [To give the panels some camber]

He firmly believes in rigid battens with as little bend as possible - that's what the Chinese use. The fan arrangement of the battens means that sail twist is converted into horizontal aerofoil sections and the amount of lift is controlled by how much twist you allow.

He mentioned something about the drive coming from vortices - particularly near the top of the sail. In fact the top panel of the sail behaves very like a crab-claw sail.

Just to show that Vincent isn't all theory and no practice, he took his VERTUE around Ireland last year single handed (over 1000 miles and only had to leave the cockpit once, to redo a knot that he'd tied badly in the first place). Not bad for a 67-year-old! Although his boat has a Bermudan rig available, he much prefers the convenience and comfort of his home-made polytarp junk sail - What he calls 'armchair sailing in a boat'!

For those on the list who've never heard of him, Dr Vincent Reddish is an eminent astrophysicist who was Astronomer Royal for Scotland, and Professor and head of the department of astronomy in Edinburgh University. Maybe his greatest claim to fame is that he managed to supervise me to successful completion of a PhD in 1971! <G> He is currently leading a world-wide network of scientists in a systematic investigation into the physics of dowsing - a real but, as yet, unexplained phenomenon.

-- Bill

Bill's Chebacco News: http://www.taynet.co.uk/users/wbs/chebacco.htm

Some Junk Sail Shapes:


the well-known westernized balanced lugsail from Hasler and MacLeod. Note the lower panels are all identical, having the same measurement at both luff and leech; and the upper wedges are identical.


 from his "Gazelle" junk-schooner design. He believes in a more traditionally rounded shape than either Van Loan or Hasler. The batten-to-batten spacing is equal on the luff and the sail fans more toward the leech, unlike Hasler
or Van Loan.

Van Loan

 his ideal is a flat-headed and narrow sail. P is the batten-batten spacing.

These two drawings were scaled to be cut out for a model I was making and so nominally refer to feet, but the ratios are dimensionless. I was keeping the luff length constant.

The gray area is the higher aspect sail superimposed on the lower, but of course the sails would likely have different absolute dimensions.

Proportions are given as percent of "x", the boom length.

Yang Tze Pelican

 a junk rig on a small day-cruising boat. The Great Pelican (right) has a sail much like the canoe sails of the late 1800s, but shapewise it's not that far from the twakow sail shown immediately below...

Twakow from
William Maxwell Blake.
Sorry for the crummy scan.

An artist's rendering of the Yangtze Pelican version of the Great Pelican hull.
From V. Sokolow.

Traditional Vietnamese

(as used on Tim Severin's bamboo raft Hsu Fu; courtesy Nick Burningham)

More on Rigging Hsu Fu.


Phil Bolger's
"Chinese Gaffer"

 an interesting idea where an aerodynamic shape is combined with Chinese-style multiple sheeting points for sail shape control and light sheet loading. Bolger has sketched out at least three approaches which have appeared in magazines, and his book 103 Small-Boat Rigs includes longer essays on three rigs which incorporate the Chinese Gaffer. The idea is a cruising sail which also has good upwind performance.

This one (right) has a single sheet to the yard, and another single sheet to the battens. The hauling part of the sheet starts at the top batten via pairs of sheetlets and is the version which has been tested in use.

The version below on the "Micro Navigator" perhaps owes something to the Florida sharpies of Commodore Munroe's day, which had high-peaked battened gaff sails with a sprit-boom but only a single sheet. This sail is small and has 3 separate sheets.

Slocum: Liberdade

 Joshua Slocum built and sailed a "dory-canoe" from Brazil to the USA before he ever sailed alone around the world. This is a great
book (it's online here).

One of the few extant photos:


 His ten volume set of monographs contains umpteen sketches of boats and sails.


 "Voiliers d'Indochine" shows Vietnamese boats in detailed sketches.

A Sail on a Peero

 The framework for a small Reddish-type sail for the Bolger Sailing Peero.


 English yacht Heathen Chinee, dual centerboards and lugsails. Note jib battens.
This boat was only about 24ft on the waterline. Something on the boat was published in Forest & Stream and I'd like to find out more.


At one point I prepared some drawings based on a 174-sq. ft. junk sail described in a U.N. fishing report as something which could be effectively rigged by impoverished fishermen. Click on them for the full-size GIFs. The drawings are
not really to scale.


RiggingMaybe it doesn't have to be as elaborate as this lake-trawling sampan.
There are loads of ropes tied to a junk rig. It's baffling. It was for me. Fortunately, most of them are set up once and that's it. When you look at each line by itself and understand its purpose you see it's not such a mess at all. One benefit of all those lines is that stresses on any one part of the rig are very low. The highest stresses are probably along the luff since you want a nice taut luff on your sail.
Note: I've been working on a way to present this information and it's a little more complicated than I anticipated - the presentation, not the actual knots and lines, but we will get there.

There are two basic approaches: a multipart mainsheet with euphroes and multiple sheetlets, or a single-part mainsheet with a single sheetlet to each batten. Traditional Chinese sails, and Colvin and Hasler's ideas, fit in with the first. Van Loan and Phil Bolger subscribe to the second.
Note: this page isn't ready yet.


2.5 12/08/00