Thursday, September 25, 2003

Ancient Chinese Sail Design -- 2000 Years Old and Still Going Strong (古老中國風帆設計)

Ancient Chinese Sail Design -- 2000 Years Old and Still Going Strong (古老中國風帆設計)

Ancient Chinese Sail Design -- 2000 Years Old and Still Going Strong

The full batten sail is a Chinese invention. No other seafaring civilization has ever created a sail design even remotely similar. Invented over two thousand years ago, the junk rigged full batten sail is a marvel of nautical engineering. Developed as a commercial rig, it was highly efficient and turned a profit for its users, otherwise it would have been quickly abandoned. It made use of inexpensive materials, yet achieved amazing results. A dizzying variety of junk rigs and junk hulls were developed, specifically tailored to different cargo, water and weather conditions. Larger junks are supremely seaworthy and display superb blue water voyaging characteristics. A junk rigged full batten sail is a snap to build, rig, handle, reef, and maintain. It requires no complicated or expensive hardware, such as winches. It imposes exceedingly low stresses on the rigging. It provides a low center of effort and as a result requires less beam width and keel depth.

Compatible with Any Hull

The junk rig is compatible with virtually any hull imaginable. It has been successfully installed on inflatables, dinghies, racing yachts, cruising yachts, motor fishing vessels and large commercial craft. High tech adaptations of the full batten junk sail can be found on everything from 70 foot Americas Cup racers to 40 foot blue water voyagers, from 18 foot Hobie Cats to 7 foot windsurfers. Traditionally sampans and junks up to 30 feet feature one sail. Junks between 30 feet and 40 feet feature two sails. Junks over 40 feet feature three sails, and so on, all the way up to the 400 foot leviathans built during the Ming dynasty. But this rule has many exceptions, with no evidence to suggest that more or fewer masts are more efficient. To achieve the greatest versatility with the rig however, the hull should be shallow draft and light displacement, enabling one to explore coastal shallows, to sail up canals or rivers into inland lakes in addition to crossing blue water. The traditional junk mast is unstayed, and instead supported from the keel of the boat. Deck stepped junk masts, while non-traditional, are also feasible. A modern schooner or ketch configured along the lines of a traditional Chinese junk requires only two junk sails and two halyards. Nothing more. On a longer vessel, a junk rigged mizzen or foresail can be added.

Upwind and Downwind Performer

Junk rigs are capable of superb windward performance and can often outreach and outrun boats fitted with more conventional sail plans. A junk rig will enable a boat to sail as close to the wind as the hull will allow. Junk rigged racing yacht hulls usually achieve 35 degrees to windward. Junk rigged cruising hulls usually manage 40 degrees. The notion that junk rigs are poor windward performers is a myth; a misperception based on junk rigs fitted to lumbering, load-carrying hulls instead of racing hulls. When making comparisons one must not forget that many Bermudan rigged hulls perform poorly to windward, meaning they cannot sail closer than 55 degrees to windward, despite what Bermudan fans may claim. The reason is a Bermudan rig must be sailed with racing precision to yield good results, whereas the junk rig can be sailed in a relaxed, laid back manner, yet produce the same results. Off the wind, the junk rig is even more efficient, with its large sail area high up and full battens that boom out the sail. A Bermudan rigged boat must hoist a spinnaker just to keep up with a junk rigged boat of the same length. To add to the misery of the overtaken Bermudan rigged boat skipper, the unstayed mast of the junk can even accept a ghoster or cruising chute.

Reefing Speed Champion

It is difficult to overstate the value of being able to instantly reef or completely lower the sails on a sailing vessel in response to constantly changing sailing conditions. The junk rigged full batten sail has precisely this capability. It can be reefed in the blink of an eye, as easily lowering a Venetian blind. The ease with which a junk rig can be reefed must be seen to be appreciated. Junk sail expert Robin Blain recalls the first time he saw a junk sail reefed. He was a passenger on a boat called the Migrant, and was considering using a junk rig on his own boat, then under construction. Out of curiosity Blain asked the skipper how hard was it to reef a junk rig. The skipper had just passed around mugs of hot chocolate, so Blain expected the skipper to settle in his seat and hold forth on the subject. Instead the skipper sauntered over to the mainmast and with one hand released the main halyard, allowing it to slip over the belaying pin. He payed out half of it, then belayed it again. The sail was reefed. The skipper never set down his mug of hot chocolate and never spilled a drop. The junk rig was "user friendly," long before the industrial era term was invented.

Stress Free Rigs

Sailing enthusiasts accustomed to Bermudan rigs are in for a surprise their first time aboard a junk rigged boat -- a pleasant surprise. Junk sails are eerily, uncannily silent. They do not flap or flog while passing through the eye of the wind, whether one is tacking or jibing. The full battens preclude such antics. Furthermore the low tension in the running rigging prevents noise and chafing. Finally, a full set of sheets lead to each batten on a junk sail. These multiple sheets make the junk sail self-tending and the sail shape highly controllable. They also make jibes extremely gentle, including the inevitable unanticipated, unintended jibes. No jarring, unwelcome surge of adrenalin follows when someone inadvertently cranks the helm too far over. The fact that a substantial portion of the sail is positioned forward of the mast and acts as a counterforce further augments this "soft jibe" effect. All of this makes the junk rig highly forgiving for family sailing, where comfort is a consideration, or for long distance voyaging, where long term fatigue is a consideration.

Stress Free Sailing

Because junk sails have multiple battens, the stress on the fabric in each panel is surprisingly light. As a result a junk rig can be assembled from almost any material imaginable. Modern junk sails are usually Dacron polyester, but can be acrylic, cotton, canvas, polyethylene, even old flour sacks! Sail cut is not critical, and junk sails are typically built flat rather than cambered. Masts, yards, booms, battens can be made of wood, hollow timber, metal tubing, fiberglass tubing, carbon fiber tubing, and of course the traditional bamboo. The junk rig, like the gaff rig, uses soft lines, not stainless steel wire and winches. The motion of a boat with an unstayed mast junk rig is far gentler than a boat with a stayed mast Bermuda rig. Crews feel less fatigued at the end of a days sail in a junk rigged boat than they do in a Bermudan rigged boat, with its sharper, more abrupt movements. These advantages may not be apparent to people who have never sailed junk rigged boats, even if they have read about them.

"I bought Migrant in 1991. In 1994, with the same [Chinese junk rigged full batten] sails Dick Johnson used to go to Australia, New Zealand, Pitcairn, Mexico, and back to Bellingham, I sailed from Bellingham bound for Mexico. I spent a year and a half in Mexico before sailing onward to French Polynesia, Samoa, Tonga, Fiji, the Marshalls, Micronesia, down to the Solomons, Vanuatu, New Caledonia, and Australia. By then I had put four more years in the tropical sun on the same sail cloth, and it had become very fragile. On the way up the Barrier Reef, the top panel started developing tears. By the time I had crossed the top of Australia, the top panel was in shreds and only the bolt rope around the perimeter was holding the sail and yard together, yet the sailing performance did not suffer in any noticeable way. The sun damage in the lower panels was severe enough that a careless push with my hand would go right through the sail. [Yet] even in bad squalls the rips did not propagate because of the low stress on the cloth. I continued onward through Indonesia, Singapore, Malaysia, and Thailand. I finally replaced the sails in July of 2000 when they became too disreputable looking, even for me. What other rigs exist where a rip in the sail is not of any great concern, or that you would be able to continue onward for that many miles using sails with cloth so old and fragile?"
-- William Servais,
skipper of the junk rigged schooner Migrant

Explanation: Junk Rig Association Newsletter, What About the Junk Rig?
Illustration(s): Traditional Chinese Junk Rigged Ship, Western Hull with Chinese Junk Rigged Sails, Hobie Cat with Full Batten Sail, Neil Pryde Full Batten Windsurfing Sail
Author(s): Bruce Roberts, Michael Kasten
Affiliation: Junk Rig Association, Kasten Marine Design
Publication Date:
Original Language: English
Editor: Bevin Chu, Registered Architect

No comments: