Elliott Pattison Sail Trim guides
Sailing with friends and clients
the most often ask question I get is "how do I trim my jib". That's
not surprising because there are more variables in setting it correctly than
there are with the mainsail, but armed with a few quick basics you can quickly
take the mystery out of it. Whether racing or cruising you will enjoy sailing
more with a well trimmed sail and it is important; both for performance and for
the longevity of your sail.
To start you need to understand
that any good sail designer has to work with the rig parameters of your boat.
The spreader locations, lengths, and sheeting angle are fixed while the headstay sag is somewhat adjustable, so knowing these the
designer will develop a sail shape that will work with your boat. With this in
mind your starting point for medium air is setting the sail so that it sheets
fairly close to your rig, just missing the upper spreader and the chainplate at the deck. Start by sheeting the sail in until
either the leech comes within 3" or 4" of the spreader or the foot
comes within 2" to 3" of the chainplate,
whichever comes first. If the leech gets close to the
spreader first then move the jib lead aft until you reach the point where both
leech and foot trim correctly at the same time as the sail is sheeted in.
If the foot comes up against the chainplate before
the leech is into the spreader adjust the lead forward until both are correct
at the same time. This location should be marked as your "base"
setting.
To understand when and why you
change from the base location you need to keep in mind a few simple ideas on
what difference various adjustments will make to performance. In general all
adjustments fall into two categories; things that will make you go faster, and
things that will make you point higher. Things that make you go faster include
easing the jib sheet slightly, moving the jib lead forward slightly, inducing
more headstay sag, and easing the main traveler and
or sheet a little. Things that make you point higher are sheeting the jib in a
little tighter, moving the lead aft a bit, decreasing headstay
sag, and tightening the leech on the main. As you are sailing you should always
be aware of how your boat is sailing compared with boats around you; are you
pointing well but not going fast enough, or are you going fast but not
pointing? Once you make that determination you can then make changes that will
improve you performance in the needed direction.
In lighter air or bumpier
conditions you start by moving your jib lead forward one hole at a time until
you reach the point so that when the sail is sheeted with the leech 4" to
6" off the spreader the foot will be 6" to 8" away from the chainplate. This makes the whole sail fuller which will
increase your power. If you need to increase your pointing move the lead back a
little so that the foot is sheeted tighter to the boat making it flatter while
the leech remains 2" to 3" off the spreader. As the wind increases
and you start to get overpowered move the lead back even further so that the
foot is sheeted right in hard against the chainplate
making it as flat as possible while the leech is twisted further away from the
spreader to open the slot and let more air spill out of the top of the sail.
Headstay sag also affects how full your headsail
is; the more the headstay sags aft the more material
is pushed back into the sail making it fuller, the straighter you make you headstay the more material will be pulled forward out of
the sail making it flatter. Controlling it can be hard but in general for
masthead boats it comes from backstay tension, for fractional boats with inline
shrouds it comes mostly from runner tension, and from boats with swept aft
shrouds it comes both from shroud tension and backstay tension. For more on how
these work together see my article on Controlling Headstay Sag because it can be quite involved and requires
more in depth study than this article.
Here is a short list of basic
settings you can use as a guide to get you started. All boats and all sails are
slightly different but these guides will at least give you a good reference
point and an idea of the type of changes you make for different conditions.
Medium air 7-10 knots: Headstay
sag should be around 2"-3" (for properly designed medium headsail). Jib lead is set
so that when foot is within 2"-3"
ofchainplate the leech is 3"-4" off upper spreader. Luff should have hint of wrinkles
Light Air: Let headstay
sag back a little more, luff
should have some wrinkles. Adjust lead so that foot 4"-8" off chainplate
when leech is 4"-6" off upper
spreader.
11-14 knots: increase headstay tension as wind increases to try and keep sag as
low as possible. Tighten luff to just remove
wrinkles. Adjust lead so that foot is up against chainplate
when leech is 1"-2" of spreader.
Heavy air: Change sail if possible.
Get headstay as tight as possible. No wrinkles in luff. Move lead aft so that foot is stretched tight around chainplate and leech is 3"-4" of spreader, more as wind
increases.
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