Thursday, July 18, 2013

Cat-Ketch if you can.

Tanton 45.
Tanton 43

- It has been a while since I have had a look at cat-ketch yachts and unstayed rigs.

- The following is from a small brochure printed years ago and serves the base for the present study of a new 40' version incorporating what I have learned about this type of cruising boats over a period of 35 years since the first O.G.VW. 37 and the Tanton 43 followed by the 45 appeared on the scene.

- How did the cat ketch rig develop?

- The rig was developed and utilized on various craft throughout the past 2000 years, and was particularly popular on the Chesapeake Bay and with Yankee fishermen seeking a means of sailing their work vessels single-handedly and efficiently. It proved its worth. Like the 5-speed auto transmission that does the job while reducing cost, weight, and fuel consumption, the cat ketch did the job for those working sailors. The same holds true today. Cost, weight, and crew considerations, plus the increased desires of sailors to "try on their own" have contributed to a new, renewed I hope interest in the cat ketch rig.

- What so different about the cat ketch?

- First, there the amazing absence of clutter on deck. Consider all the head stays, shrouds, spreaders, turnbuckles, and another rigging aboard most yachts. Consider the inventory of headsails and spinnakers to content with- not to mention the attendant sheets, blocks, running rigging, winches, travelers, tracks, etc. All are gone!

-That is the first difference.

-The second is the ease of handling. Having eliminated the usual clutter, you now simply attach the halyard to the sail, hoist the sail and enjoy sailing. Coming about becomes a simple matter of putting the helm over. To return to the original tack, turn the wheel the opposite way. The sails are self-tending. Should you need to adjust one, there are but two sheets to consider. Dangerous crashing booms are gone. Foredeck work is eliminated. You seldom leave the cockpit. And in the event of a person overboard, retrieval is a simpler, single-handed maneuver.- The third is performance: nothing short of outstanding. But we will discuss that aspect further along.

- What are the advantages of freestanding spars versus stayed spars?
Stayed masts are supported by wire stays, each of which relies on fitting at each end to attach it to a tang or a turnbuckle, which in turn must be fastened to the mast or deck. The average 30' ocean cruiser has over 30 of these vital connecting points, and the failure of anyone means the probable instant loss of the mast. To effectively support the mast the whole network of stays has to be pre-tensioned which creates an enormous downward compression load on the mast, with a corresponding upward load on the ends and sides of the hull. This has created a whole modern generation of boats that are artificially strained before they ever meet the demands of wind and wave. You may recall, they used to put wires on airplanes wings. But that primitive approach was quickly discarded in the name of better safety and efficiency. Pilots simply could not trust their lives to an elaborate network of wires- the failure of any one of which meant the wing would fall off.
So aeronautical engineers developed the free-standing wing as a simpler, safer solution. The free-standing spar has evolved for exactly the same reasons it is a simpler, safer solution because it is free to flex under load without high compression strains and without depending on a series of potential failure points. And it allows for new creativity in simple, safe, and swift sail employment.

- Freestanding masts are engineered and developed to accept bending forces and torque, without worry about compression loads that no longer exist. They are then installed in a boat where the deck structure has been designed and built to become an integral connecting structure with the hull-similar to the fuselage of a modern aircraft. A mast's only purpose is to support a sail's luff. Modern engineering and material technology now provide this capability without wires, as is the case with airplanes' wings. Why then must we continue to complicate our sailboat rigs or our sailing enjoyment?

-What is the safety record of free-standing masts?

- In the past 30 years, hundreds of cat-ketch yachts have made numerous passages, both coastal and offshore. Most used aluminum poles/ masts-although an existing material, called carbon-fiber, was beginning to come in use. One is hard-pressed to find evidence of free-standing mast failures during this period-while stayed masts have continued to buckle and break away every year.

-What about aluminum vs. carbon-fiber?
Spun aluminum masts, properly engineered and developed to handle bending moments, have proven satisfactory for smaller catboats and cat ketch yachts. High, frequent stress load is not continually encountered in smaller vessels, as they may be in larger ones, therefore it is not always necessary to pay the increased cost of carbon-fiber masts for smaller vessels. Carbon-fiber is a modern material that delivers many times the strength of aluminum or other materials of the same weight. It has been used in golf clubs, tennis rackets, aircraft, and aerospace vehicles for its unique qualities of lightness, stiffness, and strength. When one considers a larger vessel, or where one considers offshore use, carbon-fiber becomes the material of choice. Its superior qualities become even more important as boat size increases.

-Are there differences in carbon-fiber masts?
Note: The description refers to the original building method of the spars for the T43 and 45, and no longer available due to the lack of demand. Still, the best way to build a composite spar, but over the past 30 years, many mast production builders can tackle the job in various ways with good results.

-Yes, Most carbon-fiber components-such as masts, poles, rudder posts, etc.-are fabricated today by what is known as the "hand lay-up" method. Carbon-fiber material is hand-layered-sometimes alternately with glass cloth- and the whole is bonded with epoxy, polyester, or similar resins. Such masts are used today on most cat ketch yachts. However, these spars have no accurately known stress loads or predictable performance capability. They may or may not do the job required. The most sophisticated, and the best method by far, for fabricating carbon-fiber and fiberglass composite masts use computer designed and operated filament-winding technology. Along with high-grade epoxy resins and heat curing, it is the same technology employed in aerospace and missile projects. This level of sophistication results in exact fiber patterns, void-free laminate quality, accurately known stress loads, and predictable performance in masts and components.

-Why the wishbone boom?

- The wishbone boom is, again, an idea from the early days of cat ketch-rigged vessels. It simply acts as a force arm to provides the benefits of both booms and vang-without the usual clutter of winch, lines, battens, hardware, etc. This boom sets at approximately a 30-degree angle to the sail's luff and creates force vectors that counterbalance those created by the sail, thereby allowing a regular (soft type) sail to be set with a draft and camber similar to that obtained by vang, equipment and crew required with a straight boom and full battened sails. Because it operates on a free-standing mast, it can be freely rotated 180 deg. about the spar without changing the sail shape. That is why cat ketch-rigged boats sail so well off-wind: the wishbone boom maintains a near-perfect airfoil shape on all points of sail. It would make sense to eliminate wishbone booms only if sails could be developed having proper camber and draft on all points without booms at all. I am tackling the problem with the new Model T. 40 I am working on and I believe I found a solution in exploring the possibilities. Should one desire a straight boom and/or a full-battened sail it can easily be made available. Frankly, however, I do not recommend it unless you have a specific reason for wanting such a rig and are willing to accept the added equipment, cost, and inconvenience that will accompany it.

-What kind of performance can be expected?

-Generally speaking, a properly designed cat ketch yacht will sail as fast if not faster than other rigs of comparable size overall. Off the wind, it will easily out-perform them because the sail's shape and efficiency remain constant and are unhindered by standing rigging-thereby increasing efficiency. To windward, it boasts the advantage of reduced weight and windage aloft, constant camber and slot effect, plus exceptional tacking ability. There is a problem, however, with most cat ketch boats that reduce that efficiency: their hulls are little more than a modified sloop or cutter designs, whose stayed rigs have been replaced by cat ketch rigs. Since a sloop or cutter hull is designed-as described earlier-to withstand stresses peculiar to the stayed rigs, it follows that that hull will not perform the same as a hull properly designed, balanced, and constructed to suit the cat ketch rig. Tanton Offshore Cat Ketch Yachts have been designed from the keel up as legitimate cat ketch yachts. And they are the only yachts on the market today that have been. This reflects in the spectacular cruising performance of these vessels. Add light hull, no standing rigging, the most aerodynamically efficient cat ketch mast ever built, modern underbody, extra-long waterline, minimum wetted surface, favorable sail area to displacement ratio and you get the kind of speed that gains your respect-racing or cruising.

- What about catboats vs. cat ketch yachts?

- Cat rigged boats (one mast on the bow and only one large sail) are useful and quite popular for simplicity and handling as long as their size is kept rather small. Once hull size reaches about 30-foot or larger, however, having only one mast forward and one sail begins to pose certain problems. The single mast becomes too large and too much of a moment-arm at the forward-most part of the boat. The sail becomes too large for easy handling and the boom begins to take on dimensions as large as many masts. Complicated lazy-jack systems may be required to accommodate furling, and windward performance begins to suffer. The cat ketch rig is the logical extension of the unstayed rig concept for employment in boats of larger sizes. It creates a better balance in the boat, provides slot effect aerodynamics, and improved windward performance. It allows for much more manageable sail size, keeps boom length within reasonable limits, and creates better sail shape by preventing pinching of the sail by the boom (that occurs when a single sail becomes overly large in use with a wishbone boom). Splitting the sail plan into smaller, more efficient components as sail area increases have long been considered by designers as the most sensible way to canvas larger boats, this to be true whether a ketch,  yawl, or schooner.

-Wish cat ketch designs are available today?

- Not Many, if any. However, since their re-introduction into sailing circles in the mid-1970s, cat ketch yachts have been seen in yacht harbors and on the oceans of the world. And because of their demonstrably superior performance of handling, the serious sailor cannot ignore them. With the exception of Tanton Offshore Yachts, however, cat ketch builders predominantly use sloop or cutter hulls, wood, aluminum, or bulky hand-layed up carbon fiber masts, inadequately designed or constructed wishbone booms; or even the straight boomed sail, with its vang and extra hardware. In spite of this, they generally perform well-which only goes to prove the inherent worth of this rig. But, as mentioned earlier, I want to offer yachts that have been properly designed and built as authentic sea-going cat ketch yachts. The new 40 represents a major design and building improvement in the use of unstayed rigs. They represent a refinement of the simplicity, comfort, and performance of the unstayed rig to the ultimate. The T. Offshore cat ketch offers versatility: for local harbors, the oceans of the world, or comfortable living aboard. Well built and economical, they offer features and performance not found in any other boats in their size category-whether stayed rig or not.

50' Millennium Falcon.

66' Magie Noire.

Tanton Yacht Design Archives.
- The manuscript originally is written in 1994 by Ian Galletti and published in a major British sailing magazine.

My latest Cat-Ketch commission!
- For a 48' Aluminum, ballasted centerboard with a free-standing rig.

1 comment:

  1. Search. For something a little different see: From JR to Elia.