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Notes from the Woollahra Tasar Clinic - Part 1

Frank Bethwaite 

Note re “Factory Settings”. 
Surprises happen! A 49er Olympic crew suffered a disaster and required a new rig immediately prior to the recent games. They had lost both their gear and their secret and painstakingly accumulated rig tension etc data. Julian carefully set up their new spars and sails all at the middle of the factory settings. When they sheeted on, they found they had a boat at least as fast as any in the fleet. They sailed well, and won Gold. 

Design Object 
The Tasar in 1975 was as revolutionary as the 49er in 1996. A dad and mum no-spinnaker toe-strapper, it held or beat the gun trapeze and spinnaker racing boats of its era. How? Its hull was unusually light, unusually stiff, and well shaped. Its foils were unashamedly low-drag laminar flow. Above all its rig was designed on the assumption that the wind was never steady, and was not only aerodynamically efficient in static shape, but was deliberately springy so that it could flex and make use of and sail faster in that unsteadiness. 
These notes describe the thinking behind our “factory settings”. 

Factors which Affect Static Sail Shape 
Shroud Tension 
Shroud adjusters should be set so that shrouds are just taut with both stay slides right forward. Object - lee shroud should go just slack with slides half back when hiking at maximum leverage. This gives the correct forestay tension and sag for the design jib fullness.at the design wind (11 to 12 kts). Pulling slides fully back in stronger wind tightens the forestay and flattens the jib. 
Jib Luff Tension 
Set to just eliminate horizontal wrinkles. Another way is to tighten until vertical wrinkles show down the luff, then ease until they vanish. With a near-new jib both ways give the same tension. Never over-tighten. 
Mainsail Battens 
Euler crippling loads- 
1 (Top) 4.6lbs, 2.1kg 
2       4.1     1.85 
3       4.1     1.85 
4       2.9     1.3 

5, 6 and 7 Irrelevant. 

Do not taper. Battens “knuckled” forward can be fast upwind in steady breeze and flat water, but are slow upwind in light air, and slow upwind in unsteady wind, and slow when reaching. 

My authority for these statements are experiment and observation but primarily model aircraft glide tests with different wing sections. The dynamics of sailing to windward at max VMG in lighter wind are the same as the dynamics of a glider which is looking for minimum sinking speed. A test model with a wing with a thin section and max camber at 25% from the leading edge was efficient at one particular speed. With a wing of identical shape and weight but with max camber at 50% (ie. a circular arc section) it was as efficient as the “knuckled” section at its best point, but it maintained this efficiency over a wide speed range. In smooth air the two sections could glide and lose height as well as each other. In rough air the knuckled section became unstable and the model sank faster, while the circular arc section continued to fly steadily in the rough air, the model remained stable and sank more slowly. 

Datum Marks 
Pilots use “check lists” or “drills of vital actions” to ensure that they repeat the configuration of their wing flaps and slats as they shed speed at each stage of every approach. Typically, “flaps 20%” at a little less than twice stall speed is the configuration for minimum power, minimum sink and lowest drag for holding and entering the circuit. Flaps 70% gives more lift and admits lower speed down the glide slope. Flaps 100% gives maximum lift for the final few hundred metres where the pilot slows to threshold speed. As I developed adjustable rigs I developed the datum mark system for my own use. Other crews instantly appreciated its value and asked me to put the dots onto their boats because it enabled them to set and repeat established efficient settings easily and accurately. 

The dots are positioned as follows:- 

One Dot Light air. For sailing to windward in winds 0 to 6kts

Downhaul - Female gooseneck on platform of mast gooseneck. Mark mast With one dot opposite downhaul cringle. 
Rotation 45 degrees (stop inside cage). 
Outhaul - 8% (ie. 8” or 200mm) camber at middle of lower batten. (Boom is app. 100” long, so at the foot 1” equals 1% camber). Mark the boom opposite a knot in the outhaul line. Mark also the knot position for 12% camber with a sharp arrowhead (for close reaching), and for 16% camber with a broad arrowhead (for broad reaching ) 
Vang - Eliminate the diagonal wrinkles which radiate from the batten protectors. Mark the plastic opposite the pivot of the block. 
Jib Slides Against inboard stops. Mark the deck adjacent to the stop plungers. 

Two dots Moderate air.  Settings for 12 kts. 

Outhaul - 4% camber at middle of lower batten. Mark opposite knot. On a production boat the knot is at the block hanger for the vang at this setting. Rotation 45 degrees. 
Mainsheet - Tense to the point where the topmast just begins to bend back and the top four battens begin to flatten. Mark the mainsheet midway between the boom block and the floor block. With a new mainsail, as the sheet is tightened the leech will become taut, the top four battens will crumple fractionally, then start to flatten. An older sail does not crumple.
Downhaul - Tighten sheet until the mark is ¾ down toward the floor block. Adjust downhaul to eliminate diagonal wrinkles from the batten protectors, and mark two dots. 
Vang - Ease sheet until mark is ¼ down from boom block. Set vang just taut, and mark. 
Jib Slides - Against inboard stops - same as Light air setting. 

Three dots. Strong wind. 

Rotation 45 degrees. 
Outhaul - Tight, and mark. 
Mainsheet - Slack 
Downhaul - Leave at two dots. 
Vang - Tighten until the lower batten reverses near the mast, and mark.
Downhaul - Tighten until the batten resumes its smooth (near flat) shape, and mark three dots. 
Jib Slides Set out four holes, and mark

Mast bend and Batten protectors. 
While the mainsail is flattened with “three dot” outhaul, downhaul and vang tensions applied, check the mast bend. When viewed from abeam the mast and topmast should adopt a smooth continuous curve which exactly matches the luff curve of the sail. When viewed from ahead, the topmast should curve out to windward about 6 to 8 ins. Also check the batten protectors. Any error in positioning is revealed as diagonal wrinkles which radiate from the protector. Reset any offending protector closer to the mast. Do not be too enthusiastic. The closer the protectors are set to the mast, the harder it becomes to hoist the mainsail.

Static Check 
Put the boat on its side with a support under the hounds. Set to two dots and tighten the mainsheet until the mark on the sheet is 75% down from the boom block. 
The leech tension should be about 40kg (90lbs). 
The camber at each batten as a per cent of the batten length should be -
 10%, 10%, 10%, 10%, 8%, 6%, 4%. 
When the underside of the sail is viewed from beyond the masthead, the leading edges of the top four battens should all fall away from the mast at the same angle. If this is not the case (say a replacement batten) I taper the offending batten until it conforms. This is the only situation where I taper a batten. 
When the leech is forced down about 300mm at Nos 3 and 4 battens - to simulate a 10 degree twist under wind load - the battens at the leech should all lie parallel with the centreline. 

That defines the designed static shapes of the sails at the one, two and three dot settings. I believe that these settings are as fast as any to windward in winds of 6, 12 and 20kts and flat water. In general, as the water gets lumpier the sails should be set progressively fuller and more twisted. Correct static shape is only the start. 

Continued in part 2

Posted 2001/08/02

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