Tasar Datum Marks

First, follow the instructions in Checking the Rig

Datum Marks

Datum marks enable known efficient sail shapes to be repeated quickly and accurately.

The code, for fastest shape to windward, flat water, is
0 to 6 kts     One dot
11 kts (design wind)     Two dots
20 kts     Three dots

The dots are positioned as follows:-

One Dot - light air. For sailing to windward in winds 0 to 5kts
Downhaul - Tension until female gooseneck lies on platform of mast gooseneck.
Mark mast with one dot opposite downhaul cringle.
Rotation - 45 degrees (stop inside cage).
Outhaul - Start by putting a knot in the outhaul; and adjust its position so it lies above the upper rivet of the vang block hanger when the lower batten sets with 4 inches of camber.ie 4" to leeward of a straight line from luff to leech. (the batten is about 100" long so this is 4% camber). With a new sail the skirt will lie along the boom. With an older sail the skirt will be stretched.
Ease the outhaul until the lower batten sets 8% (ie. 8" or 200mm) camber at middle of lower batten. Mark the boom opposite the knot with one dot. 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 ) Reset to one dot, then.
Vang - Tension to eliminate the diagonal wrinkles which radiate from the batten
protectors. Mark the plastic opposite the pivot of the block.
Jib Slides - Set against inboard stops. Mark the deck adjacent to the stop plungers.

Two dots - moderate air. - Settings for 11 - 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 - Very tight, and mark.three dots against knot
Mainsheet - Slack
Downhaul - Leave at two dots.
Vang - Tighten until the lower batten reverses near the mast, and mark three dots. (The tension needed surprises most sailors.)
Downhaul - Tighten until the batten resumes its smooth (near flat) shape, and mark three dots. (This tension, too, is severe.)
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
Also check the batten protectors. Any error in positioning is revealed by diagonal wrinkles which radiate from the protector. Reposition any offending protector closer to the bolt rope.