|Common trimming errors
Itís not usually too hard to get your mainsail trim in the right ballpark when you are running. There are, however, two
mistakes I commonly see. Both are very slow.
The first error is overtrimming the mainsheet. This is bad because you lose projected area in the sail. Basically, you
want the boom (and therefore the chord of the sail) to be roughly perpendicular to your apparent wind.
To find the right position, ease the sheet out until either a) you see a bubble along the front of the sail (at which
point you should trim it back slightly to remove the bubble); or b) the boom hits the leeward shroud(s); or c) the boom
reaches an angle of roughly 90į to (the centerline of) the boat.
To avoid overtrimming the main, donít cleat the sheet. Though the mainsheet is often eased as far as possible during the
run, there are always small changes in wind angle or pressure that might require a trim change. If the mainsheet is
cleated, odds are that it will be forgotten and seldom adjusted.
The second common error is using too much vang downwind. Itís easy to over-vang on a run, but in most cases you want only
enough tension on the mainsail leech so the top batten is parallel to the boom. If you pull down too hard, the top
batten(s) will hook windward. This reduces projected sail area and will kill any air flow that might be happening around
the top part of the sail. Too much vang is a little like overtrimming the sail. It is usually quite slow, especially when
you have light air or lumpy seas.
Another time you definitely want a looser vang is when youíre sailing a boat where the leeward shroud prevents the boom
from going out all the way. In this case you cannot get the bottom of your sail perpendicular to the apparent wind. By
easing the vang, however, you allow the top of the mainsail to rotate forward so it may be 90į to the wind. This trim is
Other mainsail trimming tips
Beyond easing the sheet out far enough and not tensioning the vang too hard, there are several things you can do with the
main to make your boat go faster on runs.
ē In lighter air you may have to hold the boom out, especially if you are heeling to windward. When you do this, try not
to pull down on the boom since this will likely create too much leech tension.
ē Trimming the mainsail and spinnaker often go hand in hand. For example, when you ease the spinnaker sheet you may be
able to ease the mainsheet, too. If the two trimmers communicate, they can often help each other.
ē On smaller boats, many helmspersons play the the main by holding the sheet directly as it comes from the boom. By
skipping the ratchet block you get a better feel for the sail, plus itís easier to pump it out and let the sail out.
ē You almost always want less mainsail luff tension on a run than on a beat. This is partly because the mast gets
straighter downwind and you donít need luff tension to pull the sailís draft forward. In fact, you want the draft further
aft so you should ease the cunningham completely and even lower the halyard if necessary to get a nice fair shape in the
ē The air flow around the mainsail is mostly stalled when youíre sailing downwind, so donít rely on telltales (either on
the leech or near the front of the sail) to give you much information about trim.