File - Canadian Wayfarer Association

3 The final guide is that sometimes the luff curve of the sail and the bend of the mast
match so well that all the available fullness is used up. Then the sail becomes so flat
that it cannot support the roach (= leech) which pivots to leeward about the straight
line from head to clew. As the aft edge of the sail bends away, the inner end of the
battens often sticks up in an unsightly S bend.
.....
Power will be lost, pointing will be poor and there will be no off the wind speed. The
solution is to straighten the mast more by lengthening the spreaders and angling them
further forward. Experimenting with the mast is best done outside the race situation. In
the race itself, too many things are happening, making it impossible to concentrate on the
work that the spreaders are doing. Try differing rigging tensions, because the slacker
the rigging, the less work the spreaders will do. If possible, try to see your boat from
outside to calculate from a distance, the effect of these changes.
Wind tufts should be fitted to leech of the main. The idea is that they should stream aft on a
properly set and trimmed main sail. If they bend round to the leeward side of the sail, the air
flow on that side has broken down because the leech is too tight. So ease the vang and/or the
mainsheet. If they bend round to windward, the leech is too slack and the vang and/or mainsheet
need to be tightened. Beware however, of watching the windtufts too slavishly. In fluky
conditions, they can be too twitchy.
One very important guide to leech tension is that the whole mainsail luff should backwind at the
same time. If the upper luff backwinds first, the leech is too slack.
Finally, the job of the cunningham is to provide extra tension to the luff when the mast has been
bent and the distance between the black bands thus reduced. It must not be over-tensioned.
Otherwise a vertical ridge is created behind the luff and the leech is opened out. The correct
way to use the cunningham is to bend the mast with the vang and/or main sheet to get the top
batten and boom in proper alignment, and then to tension the cunningham sufficiently to remove
any luff creases. If in doubt, leave well enough alone and accept the creases.
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