The Boat Barn Web Page
Home | Beach Cruiser | Sailing Dory | Badger Builders

Previous

 
Arne K's Page
[In the following article, Arne Kverneland describes his experiments with bending battens and cambered panels and how to make them]

Malena and her Junk Rigs:

From Bermuda Rig to Junk Rig.


Malena is a 23' fin keeled Albin Viggen. Built in 1972, I have owned her since '81. I cruise her mainly on the South-west coast of Norway. In 1990 I converted her rig from Bermuda sloop to a junk sloop. The tales about ease of handling, hoisting sail, reefing and furling soon turned out to be true. Her speed before the wind was equally impressive. Upwind on the other hand, she did not shine, especially not in light winds. I had read that this was the case, but was still surprised since I had increased her sail area from 27 to 32 square meters (sqm). The sail was of the McLeod style sail with 7 panels. And the sail was flat as a wall (Photo 1) . I soon started to wonder if this flatness of the sail was the reason for the lack of drive.


Photo 1

From Flat Junk Sail to Hinged Batten Sail.

In 1991 I decided to try to make a junk sail with camber in it. First step was to make hinges in the battens, so that they could bend to a simple curve. This would introduce camber in the original flat sail. The fine thing with hinges is that they swing out to the stops and ensure that the camber stays pretty constant, not depending on wind strength. This was a great success. Malena felt as if she had had her sail area doubled. Both pointing angle and speed to windward were improved, and so was her general light wind performance. I sailed with this setup for a couple of summers (Photo 2).


Photo 2

From Hinged Battens to Bulging Sail Panels Between Straight Battens.

Still, even if the hinges never broke down or misbehaved badly, I never felt quite comfortable with the idea of going offshore with them. To cut a long story short, after some less fortunate tries, I ended up with a method for making a cambered junk sail with straight battens. The trick was to cut each batten panel so that when filled with wind, they would bulge to a wing shape. (Photo 3 ). I made this sail in '94, and I am still happy with it. With this sail Malena is about as fast to windward as she was with the hinge batten sail. Even though I have ideas for possible improvements, I regard this sail to be fully operational and safe in use.


Photo 3

Arne's Chain Calculator
or, how I do to make guessing on camber a little less inaccurate?

This method is used to find the camber in a horizontal batten panel in a junk sail. It works quite well within the camber/chord range 5-10% at least.

1. See fig. 1. Decide where max. camber point should be (A - B).

2. Decide how deep camber you want at (A - B).

3. Mark the distance A'-B' (=A-B) horizontally on a wall and hang a chain on nails in A' and B' (fig2a).

4. Adjust chain length until you get a bight as deep as the desired camber you decided in # 2.

5. But!! A real sail will take the flatter shape of fig .2b, not the "chain shape" of fig 2a. Therefore you must make the bight or "chain camber" in para.4 about 20% bigger than the sail camber you really want. If you want a real camber/chord deeper than 10% I guess you will have to increase the correction factor from 20% to 25 or even 30%. A test panel will here be required. The reason for this oddity is, I believe, that the stretch in the sail panel from C to D (fig 1) will resist the bulging of the sail-cloth.

6. Measure how much chain you used between A' and B'. Then you can calculate the rounding you need along each batten to get the desired camber. See fig 3.

7. The calculated rounding, R, can then be used when drawing the panel. Use a wooden batten on the floor, fasten it with a few well placed nails to get the rounding you like. I prefer to cut out a template for the rounding in thick paper first, and use the template on the upper and lower side of the panel. Now I guess you understand why I prefer to make 4 or 5 identical panels! As the batteries increases above 10 deg.., everything gets a lot more complicated, and in the top panel everything is guesswork. Just remember that in the top panel the wind will blow across the panel more than along it. For that reason the camber must be small. The rounding along the yard should be guesstimated to about 1/5 of the rounding in the lower panels.

8. This is rough engineering, but don't worry. Compared to the flat junk sail it will be far superior.
PS. Maybe the camber/chord could be increased to 12 or 15% by adding about 2 cm positive rounding in the luff and leech of each panel. That would maybe reduce the problem mentioned in #5.
PS2. The leech of the two top panels are cut with about 5 cm hollow to avoid a hooked leech.

Sailing.

When sailing with the bulging junk sail, it behaves like a cross between a flat junk sail and a Bermuda sail. I get the Bermuda rig feeling upwind, with good feedback. When pinching too close to the wind, the wind will blow into the bulging sail at the luff. When I'm doing fine, the sail looks ok, and the telltales fitted to the leech will fly right out (aft). When the sail is being stalled, the same telltales fall to leeward, behind the sail.
This sail can be reefed and furled as the flat junk sail, and can even perform the let-the-sheet-fly trick without any annoying fluttering. All that extra cloth in each panel will just "float" or "swim" back and forth until the sheet is hardened in and the sail fills (Photo 4).


Photo 4

If you need to know more though, drop me a line, and maybe I can help you.
 

Stavanger 26th August 1998.
Arne Kverneland

(arkverne@online.no)

Editor's Note: Robert Laine in Holland has written a shareware program called Sailcut8 which will design Chinese sails with cambered panels. It can be downloaded free from the files area of the junkrig e-mail list at:
www.groups.yahoo.com.
 
 


Home | Beach Cruiser | Sailing Dory | Badger Builders

Previous

 
 
 

Gerald K. Limber
Asheboro, NC

gklimber@atomic.net