10
J/105 Tuning Guide
Solutions for today’s sailors
trim in once you have accelerated to
increase pointing.
The Class mainsails are fitted with a
spreader window so that you can see the
jib leech on the lower spreader. Put tape
marks on the spreader at 7.62cm (3”),
15.24cm (6”) and 22.860cm (9”) in from
the spreader tip. In general you should
trim the jib so that it is at the spreader
tip in very light air, 7.62cm (3”) inside the
tip in light air, 15.24cm (6”) to 22.860cm
(9”) inside the tip in moderate air, then
back out to 7.62cm (3”) in heavy air. These
guidelines are subject to change based
on sea state. The jib can be sheeted
harder in flat water than in waves and
chop. Be careful to only make small sheet
adjustments. Due to the high aspect
nature of the jib, small changes make a
big difference.
Jib Lead
The jib lead should be used to control
the top and bottom shape of the jib.
The middle of the jib is not as affected
by lead position as much as it is with
sheet. Once the sail is trimmed to the
appropriate spot on the lower spreader,
adjust the lead to make the top and
bottom look right. Moving the lead
forward will make the upper leech more
closed and the foot rounder. Moving the
lead aft will make the upper leech more
open and the foot flatter.
The median jib lead position is slightly
aft of the middle of the jib track, which
is about 9” aft of the chainplate. This
position is also just forward of the window
on the side of the cabin house.
Headstay Tension
Headstay tension has the most dramatic
affect on the overall camber of the jib.
Headstay tension affects headstay sag.
This is a difficult thing to visualize, but
it works much the same as mast bend
affects mainsail shape. As the headstay
sags, it pushes the luff towards the leech,
which increases camber. Conversely as the
headstay gets tight, it pulls the luff away
from the leech, decreasing camber.
Clearly this is very important, but has
been listed last here because it is very
dependent upon rig tuning. Headstay
tension is achieved by a combination of
a tighter rig and a tight backstay. As we
have learned in the rig tuning and main
trim sections, rig tuning and backstay
tension has a great affect on mainsail
camber as well. The Class main and jib
designs and the tuning guide shroud
tensions have been carefully developed
to have the backstay control main and
jib camber in unison. If you are tuned
properly, when the main sets up correctly,
the headstay tension will be correct as
well. Your headstay tension should be
almost self-tending.
During a race, the only way to adjust your
headstay tension is with the backstay.
Because of this it is important to know
how you are tuned and whether you are
actually sailing in the right wind speed
for your tuning. The backstay will be the
key to get the most of the set up that you
have when you are not tuned perfectly.
Simply, if there is less wind than you are
tuned for, use less backstay tension to
power up the sails as best you can. If there
is more wind than you are tuned for, use
more backstay tension.
A good technique is to tape a batten
with marks every 2.54cm (1”) on it to the
backstay cylinder. This will help you to be
able to record your settings and duplicate
them later.
Part 5: Crew Weight Placement
With the new “float line” rule, this
discussion has become much easier now
that we know that all boats should float
the same. The goals of weight placement
are to 1) control helm and 2) reduce wetted
surface in light air.