|By James Wharram (1997)|
Drawings by Hanneke Boon
|"It's a Gaff Sail", they say. "No", I say, "What you and the wind are looking at is a soft Wing Sail."|
Whether you see the TIKI sail as an old fashioned gaff sail or a new evolved soft wing sail is a matter of dispute.
What is not in dispute is, that since we developed the TIKI sail in 1981 for the then new TIKI 21 Coastal Trek Catamaran, over 3,000 of this type of craft, including many larger ocean sailing ones, have used developments of the original TIKI 21 sail rig. No new/old sail rig has been used on so many craft or been so widely tested.
Now, a wider public than Wharram catamaran owners is asking about the advantages of this rig.
100 years ago, in Britain, the major sail rig for small yachts was the gaff rig adapted from fishing boats. It had a short luff/leading edge and a long, heavy gaff. For windward work in light winds, one hoisted a gaff topsail (See Fig.1).
This rig had evolved on fishing boats to pull a heavy beam trawl over the quarter, its best driving qualities being off the wind. It is a rig that requires hard work and skill to get the best out of it, if used on an all round sailrig.
|In the 1930s, the new 'Bermudan' sail, with its single halyard, no gaff and no topsail, seemed to the yachtsman of the day, particularly weekend yachtsmen, who did weekend club racing, a definite step forward in an easily handled sail rig, and it did sail closer to the wind by about 5° than well trimmed yacht gaff sails.|
After 60 years of 'development', the present day Bermudan sail is no longer the simplified rig of 60 years ago. With its many manufactured fittings it has ended up being an expensive rig. It is poor off the wind, requiring a spinnaker to rectify this deficiency, which is hard to handle shorthanded or in rough seas.
In the mid 1970s, Hanneke Boon, my Dutch partner, and I, attended a series of lectures on the aerodynamics of sails, held at Bristol University, with Britain's leading authority on sail aerodynamics, Tony Marchaj, as prominent speaker.
During the lectures it was stated, that the ideal sail would have a semi-elliptic 'Spitfire Wing' or square tipped 'Messerschmidt wing' profile. It would have easily controlled camber and twist, and most important, no or minimum mast turbulence on the leading edge of the sail. How to achieve this in practice was not part of the lectures.
During the discussion on ideal sail profiles, I suggested that the Pacific crab claw sail and the Dutch high aspect ratio gaff sail were closer in profile to the Spitfire/ Messerschmidt wing shape than the tall, skinny at the head, triangular Bermudan sail.
Tony Marchaj agreed with the suggestion and later tested Pacific crab claw sails in a wind tunnel. He came up with surprising good figures showing their aerodynamic efficiency in relation to the Bermudan rig (first published in 'Practical Boat Owner' in November 1988 and later worldwide).
At the time, as a practical sailor, I could see the handling, i.e. reefing etc., difficulties of the Pacific crab claw sail and therefore did not pursue its development.
In 1981, we were designing a radical trailer/sailer 'Coastal Trek' catamaran, called the TIKI 21. A short mast, no longer than boat/trailer length, easy to raise, was to be an important aspect of the design. This excluded the use of the Bermudan rig.
The TIKI 21, built in a 'persuaded' (not tortured) ply/ epoxy/glass laminate, with wider hull separation than was then the norm in cruising catamarans and, for quick dismantling/connecting, beams LASHED to the hulls, (a practice previously done only by the ancient Pacific sailors) was a 'way-out' design.
One more 'way-out' idea, was not going to make the project more of a shock to the conventional buyer. So, (remember, my design partner is Dutch) we applied aerodynamic principles as discussed at the Bristol Symposium to the Dutch high aspect ratio short gaff rig, a rig evolved over centuries for fast passenger boats sailing in waterway Holland. (See fig.1)
The Dutch rig is superb in its standing rigging simplicity, which in itself produces less aerodynamic turbulence than a Bermudan mast carrying an equal sail area with its spreaders and numerous shrouds (See fig. 2).
The major leap forward we made, was to remove the main turbulence of the strong, large section Dutch mast from the leading edge of the mainsail by wrapping the sail around the mast in a wide luff pocket.
Tiki 21 with Wingsail rig
|Originally, we expected problems in this concept for, in the late 1970s, Garry Hoyt, an American, designed the 'Freedom' rig with tall, unstayed masts and a double layer Bermudan sail that went right around the mast, giving a leading edge to the mainsail without turbulence from the main mast. He was obviously working from the same aerodynamic principles as we. For some reason, after a few years, 'Freedom' yachts went back to conventional mast tracks and slides. No reason was publicly announced for this change, but there must have been some practical reason for this retrograde step.|
In 1981, we argued that a 'Wide Pocket' around the mast would be a workable solution to reduce mast turbulence. So, we approached Jeckells of Wroxham, our long time sailmakers, to loft our first designed sail, when we all ran into an unexpected problem.
Sailmakers now use computer software connected to Laser cutting machines. Any mainsail, which has more than three sides gets the modern sailmaking system confused.
Fortunately, with the Jeckells' family experience (going back into the last century), we were able to get around the rigid 'computer mind', but not without several badly shaped sails.
|A good way to 'test sail' a new boat is to sail it in crowded sailing waters, for example, the Falmouth Estuary near our home base, and compare it with other boats. One day, in the late eighties, smugly satisfied with our professionally built TIKI 28 design's performance in comparison to other craft of similar or longer length, we were passed to windward by a 31ft. (9.45m) schooner rigged workboat, designed for fishing and sail training (see photo, TIKI 31). The fact that it was also a Wharram design, did not lessen the consternation or pique as it passed, for 'everyone knows' that schooners 'cannot' sail closer to the wind and faster than an equivalent sized single masted boat. Well, this one did.|