Trimming
your mainsail can be made simple by following these rules of
thumb. Use these as a starting point and experiment with small
changes to see what works best for your boat.
MAINSHEET
AND TRAVELER
The two most important guides for trimming a mainsail upwind
are to keep the boom on the centerline of the boat and the top
batten parallel to the to the boom. At this point, the leech
telltale at the top batten should flow. If it doesn't, you should
twist the sail off more by easing the sheet and pulling the
traveler further to windward.
More leech
tension closes the leech, which allows the boat to point higher.
But when you trim past the point of stall, where the top telltale
stops flying, the boat will start to slow down. As the boat
begins to be overpowered, the traveler should be eased down
to reduce weather helm and keep the boat at less than 25 degrees
of heel. As the traveler is eased, you will begin to develop
backwind. This is not a problem. In puffy wind, the traveler
should be played aggressively. Choppy water usually requires
a little more twist in the leech than flat water so you should
pull the traveler higher and ease the sheet.
OUTHAUL
AND FLATTENING REEF
In underpowered conditions upwind, the outhaul should be adjusted
to keep the shelf half open. When all crew members are on the
weather rail, the shelf should be closed. If you are having
to ease the traveler down frequently in the puffs, you should
put in the flattening reef. The flattener is a ring in the leech
just above the clew. It is independent of the cunningham and
will remove a great deal of fullness from the bottom quarter
of the sail. It does not have to be entirely taken up, but rather
can be tensioned as more flattening is required. Offwind, both
outhaul and flattener should be eased to fully open the shelf.
CUNNINGHAM
AND HALYARD
Cunningham and main halyard adjust the luff tension which affects
the position of draft or maximum fullness in your main. As a
general rule, the draft should be 50% aft from the luff. In
underpowered conditions, you should have horizontal wrinkles
on the luff to allow the draft to stay in its designed position.
As the wind increases, the draft will move aft due to mastbend
and cloth stretch, so you need to add luff tension to hold it
at 50%. As you get overpowered, you should just barely remove
the wrinkles. As the wind continues to increase, add cunningham
to keep the draft at around 50%. In choppy water, the draft
should be a bit further forward (40-45%) for better acceleration.
In very flat water and a good breeze, the draft can be allowed
to slide aft to 60%.
Offwind,
be sure to ease the cunningham right off.
BACKSTAY
In traditional masthead rigs with no running backstays, the
permanent backstay controls both mastbend and headstay sag.
Mastbend is the primary adjuster of mainsail fullness. As wind
increases, so should backstay tension. We strongly recommend
a powerful and easy way to use backstay adjuster.
If your
masthead rig has running backstays, these are used to control
mastbend. They also have an effect on headstay sag. At a given
permanent backstay tension, more "runner" will straighten the
mast (making the main fuller) and remove headstay sag.
On a fractional
rig, permanent backstay controls mastbend and the runner (attached
at the hounds) controls the headstay sag. A fractional rig may
also have a checkstay which controls lower mastbend much the
way runners on a masthead work.
Whatever
your rig configuration, you need to make your main flatter as
the wind increases. Choppier water requires a bit fuller sail
for a given wind strength. You should also mark all adjustments
so you can consistently reproduce fast settings.
Off the
wind, the permanent backstay should be eased right off unless
you are power reaching, when about half of full tension should
be carried to depower the sail and support the rig.
VANG
If you have a powerful vang, you can use it to induce lower
mastbend if you want to flatten the main entry low down. In
general, this is not necessary on most big boats. Off the wind,
the best rule is to keep the top batten parallel to the boom.
Close or beam reaching, you can also watch the top telltale
and keep it flowing. On a power reach where you are on the edge
of a broach, keep a hand on the vang to dump it off if the rudder
feel as though it is stalling. Downwind in big waves and wind,
you can help stop oscillation by "overvanging" and hooking the
leech.
For more detailed information on setting your main, or any question
about your sails - contact Oriental Sailmakers. Phone 252-249-2093
or email sails@towndock.net.
