Monday, October 6, 2003

Michael Kasten on The Junk Rig (Michael Kasten 論中國風帆)

Michael Kasten on The Junk Rig (Michael Kasten 論中國風帆)

What About the Junk Rig?

Is the Junk Rig Suited to Modern Cruising?

The junk rig shares many of the virtues of the gaff rig. The junk rig or "chinese lug rig" is easy to handle, very easy to reef, easy and inexpensive to build, easy to rig, has no complex hardware, requires no winches, is easy to maintain, involves very low rigging stresses, provides a low center of effort so requires less beam or depth of keel, and at least in my view, looks great!

That is quite an impressive list of positive attributes... While the following is not intended to be a comprehensive guide to the junk rig, it is a brief introduction to a few of the advantages offered by the chinese lug, or junk rig. Due to its excellent qualities for blue water voyaging, I believe the junk rig has much to offer.

Some Advantages Specific to the Junk Rig

Reefing: The ease of reefing a junk rig is legendary. Perhaps it is best illustrated with a brief story about sailing one quite windy day off Port Townsend on Migrant, sister ship to Colvin's Gazelle. This was in 1979, and I was considering the junk rig for my own boat, then under construction. Naturally curious, I asked the skipper about reefing the junk rig. He had just passed around mugs of hot chocolate, so I expected a brief discourse on the subject. Instead, without saying anything he walked over to the main mast and with one hand released the main halyard just enough to let it slip over the belaying pin, paying out about half of it and belaying it again. The boat was reefed. He did not put down his mug of hot chocolate. He did not spill any.

Suitability to Cruising Boats: Many hull forms will handle the junk rig very nicely. As we are now seeing, fully battened sails are the "state of the art" on high performance sailing craft, for example on the America's Cup contenders. Given proper design, there is no reason the junk rig cannot be adapted to performance oriented cruising boats. An excellent combination is also the use of a fairly traditional hull form with the junk rig. As with any rig, there must be correct balance, and sufficient sail area, with an efficient plan form given to the sails. In my view, there will ideally not be any "western" sails such as a jib, and the rig should approach that of a true ocean going Chinese junk.

Suitability to Motor Sailors: A motor sailor can make excellent use of the junk rig. A motor sailor can be 100% sailing vessel, as well as being 100% capable under power. There are many other approaches as well, such as that taken by the Gulliver 46, the Greatheart 48 and the Greatheart 60 designs. These types have an emphasis on sail that is more on the order of around 60% to 70%. In other words, the sails are provided primarily for the purpose of auxiliary propulsion, rather than primary propulsion. The sails serve the function of being the "get-home" motive power in the case of engine failure. In addition, the sails provide extra boost while motoring when the wind favors. As a bonus, the sails and rig provide excellent roll dampening. For this purpose, the junk rig is ideal.

Simplicity: With a schooner or ketch configuration arranged in true Chinese junk fashion, therefore not having a western jib, there would be just two junk sails, therefore just two halyards total. For a larger vessel, a small mizzen or small fore sail can be used, also ideally a junk type of sail.

Ease of use: On any cruising vessel, be it a sail boat or a motor sailor, it seems particularly advantageous to have the ability to instantly reef the sails, or to lower them completely without any fooling around. Sail and battens collect neatly in the lazy jacks. Once down, you can go to the sail to throw a line around the battens if necessary.

Flogging / Luffing: There is no sail flapping and flogging when passing through the eye of the wind, either while tacking or jibing.

Safety: Individual "sheetlets" are lead to each batten, a full set of sheetlets on each side, so the sails are self tending. The sail shape can be controlled very effectively. This is quite a safe arrangement as well. The multiple sheets, one to each batten, make jibes very gentle, so there is no drama if someone inadvertently puts the helm too far over. This "soft jibe" effect is augmented by there being a fair sized portion of the sail forward of the mast, as a counter force. This makes the junk rig very forgiving for family sailing.

Sail Stress: Having multiple battens, the sails can be made of somewhat lighter material. Sail "cut" is not usually regarded as being critical, and most often junk sails are built "flat" rather than being cambered.

Appearance: In my view, the junk rig looks "right" on many vessels, especially so with a somewhat "traditional" hull form. Given the right match to the hull form underneath, in my eyes the junk rig is very handsome. This can even be stretched to the somewhat unusual in some cases. For example, the junk rig would be a perfect companion to a vessel like the 46' trawler Gulliver...

Spars & Rigging

Spars: Spars can be solid wood, or alternately, the junk rig can take advantage of welded aluminum tube or pipe for spars. These are perfect for the junk rig and when painted properly are nearly indistinguishable from traditional round wooden spars. Compared strictly on a strength to weight to cost basis, aluminum pipe spars are nearly impossible to improve upon.

Battens: Many types of battens have been tried, varying from the obvious use of wood, to the use of ABS pipe, and then to the use of fiberglass rods or bars. Each material has an advantage. Fiberglass battens are a bit heavier and more costly, but they will usually outlast the other types by a substantial margin.

Rigging: The junk rig is friendly to use. For example, just as with a traditional gaff rig, one will be handling soft lines rather than harsh stainless wire and winches.

Proportion: The junk sail drawing presented above is very generic, and is intended primarily as a schematic of a four batten junk (upper yard and boom not included in the batten count). In most applications, the sail's proportions would be stretched to be somewhat taller and less wide. In other words, the rig would ideally have a somewhat higher aspect ratio.

A Few New Terms

A minor advantage of familiarity with the junk rig is being able to impress dock side wags by knowing all about lizards, sheetlets, euphroes, snotters, and bowsing tackles....

Sail shape is controlled by the sheets mainly. Each "sheetlet" runs through a "euphroe" which acts as friction block to keep the tension set as intended. In my drawing, I've made use of a simpler arrangement using a fiddle block and separate "lizard" eyes in order to allow the sail to self adjust when it is reefed.

Once the sail is raised, if it is desired to tension the sail vertically, it is hauled downward by a "bowsing tackle." If it is desired to move the sail forward or aft, it can be done by controlling the "out haul" which in this case leads forward to the leading edge of the battens. The top yard can be controlled via a line called the "snotter" to move the spar forward or aft, or to snug it against the mast, as needed.

In Conclusion

There are many excellent resources for more information on the junk rig. Tom Colvin has written many good articles on the subject, as have Hasler and others. If this kind of thing is of interest, please inquire.

Kasten Marine Design, Inc.

Editor's Comments:

Michael Kasten is a modern enthusiast of the Chinese junk rig. Like many members of the junk rig fraternity, Kasten has come up with modern adaptations of the two millennia old junk rig using modern industrial materials.

-- Bevin Chu

Explanation: What About the Junk Rig?
Illustration(s): Junk Rig, Gulliver Junk Rig
Author(s): Michael Kasten
Affiliation: Kasten Marine Design
Publication Date: 2001
Original Language: English
Editor: Bevin Chu, Registered Architect

No comments: