NS J 105 Quick start guide

J/105 Tuning Guide Solutions for today’s sailors
J/105 Tuning Guide Solutions for today’s sailors
TUNE YOUR RIG
FOR OUTRIGHT
SPEED

2
J/105 Tuning Guide Solutions for today’s sailors
Contents
Pg. 3 Part 1: Rigging Preparation
Pg. 4 Part 2: Rig Set-Up
Pg. 7 Part 3: Mainsail Trim
Pg. 9 Part 4: Jib Trim
Pg. 10 Part 5: Crew Weight Placement
Pg. 11 Part 6: Downwind Sailing
Pg. 13 Tuning Guide
Pg. 14 Worldwide Service
The J/105 began what J-Boats describes as the “J/Sprit revolution”. It was the first boat of
this kind introduced and has been followed by many models. The class has enjoyed great
growth in recent years through the quality of the boat itself and the strong involvement
of its’ owners. Its attraction as a one-design race boat is its high performance, strict class
rules and limited sail inventory that promotes extremely tight class racing.
At North, we look at each sail with from a unique perspective and choose the best
construction process that we are able to produce within the class rules. We choose the best
commercially available fabrics and construction techniques, or develop our own through
North Cloth.
This tuning guide has been developed over many years of J/105 sailing and sail
development. It is intended to serve as a starting point for new boat owners and new
North Sails clients. Once your boat is set up to the basic principles of this tuning guide,
you can use our Quick Tuning Guide to make on-the-water adjustments to your rig
to make adjustments for various wind conditions. This guide is not an absolute truth,
but will put you in the ballpark. As you get more advanced, you may find that slight
alterations better suit your sailing style
Sincerely,
Ken Read
President North Sails Group

3
J/105 Tuning Guide Solutions for today’s sailors
Part 1: Rigging Preparation
The following recommendations are small
changes that should be made to the stock
J/105 to allow you to get the most from
your North Sails and make the boat easier
to sail and set up.
Head swivel shackle
The North Sails jibs come with a webbing
loop at the head. It is critical to have a
90-degree “twist” shackle to attach the
sail to the swivel. A standard shackle will
cause a hard spot at the top of the jib as
the sail is torqued.
Remove backstay toggle
Many J/105s come with a toggle that
rotates the hydraulic cylinder 90-degrees
so that the handle faces forward. While
it is nice to have the handle forward, this
toggle reduces the throw of the backstay
adjuster too much so that you are not
able to get enough tension in heavy air.
Some of the older boats actually need to
have the backstay rod shortened to get
enough backstay throw.
Change to 4:1 or 6:1 Cunningham
The standard Cunningham is 2:1 and
led aft to a cabinhouse halyard stopper.
This system should be replaced with the
lower purchase with integral cleating
shackled to the ring on the top of the
Quik Vang. This allows for easier and
more precise Cunningham control by a
forward crewmember. Many boats then
rig the asymmetrical tack line through the
free stopper.
Mark the tack line at the cleat
Put marks on the tack line at the proper
range of settings. As you approach the
windward mark you can then pre-set the
tack line so that when you extend the pole
and set the spinnaker the tack will be set
properly. The tack line is much easier to
work with in this placement than on the
side of the cabinhouse.
Fig. 1: Head “Twist” shackle
Fig. 2: 6:1 Cunningham
Fig. 1 Fig. 2

4
J/105 Tuning Guide Solutions for today’s sailors
Move mainsheet swivel base forward of
the traveler
This allows for easier trim of the gross
tune by the main trimmer, especially
when tacking.
Tapered SpectraTM spinnaker sheets
These sheets have a light uncovered
portion that attaches to the sail, with a
covered portion that goes on the winch.
The sheets should be 3/8” Spectra cored
line with the cover removed at the sail end
of the sheet. These lightweight sheets are
used in all conditions and help downwind
performance in light air. Heavy sheets
pull down on the leech of the spinnaker in
light air, closing the leech too much.
Bypass the jib sheet turning block
The standard set-up for the jib sheet is
to run the sheet from the clew of the
jib, through the lead block, through the
turning block near the rail, and then to the
winch. This set-up makes the lead block
lean over to leeward, increasing sheeting
angle. In light and moderate air, the jib will
sheet tighter to the centerline if you lead
the sheet straight to the winch from the
jib lead block. In heavy air, it can be faster
to use the turning block to sheet the jib
outboard slightly.
Part 2: Rig Set-Up and
Preparation
Tools and items required: Loos RT 10M
Rod Tension Gauge, 2 crescent wrenches,
spray lubricant, bosun’s chair and 50’
metric tape measure.
Part of the success of growth of the J/105
Class is the tight class rules and limited
sail inventory. With the J/105s limited sail
inventory of only one headsail, aggressive
rig tuning is essential for performance
throughout the full range of wind
conditions. By definition, the North Sails
“AP” inventory is optimized for 9 to 12
knots. This is actually the easiest condition
to sail in, so the racing tends to be at its
tightest. Having really fast sails in this
condition is key to gain a slight speed edge
and the AP inventory is designed to give
you just that. The heavy air “HA” inventory
is optimized for 13-20 knots. In the extreme
conditions of light and heavy air the rig
must be manipulated to enhance the sail
Fig. 3: Move the mainsheet
swivel base forward of the
traveler for easier trim of the
gross tune by the main trimmer,
especially when tacking.
Fig. 4: By using a soft jib sheet
attachment and a continuous
jib sheet like the example here;
the clew of the headsail will pass
by the mast smoother during
each tack.
Fig. 3 Fig. 4

5
J/105 Tuning Guide Solutions for today’s sailors
shapes for those conditions. The result of
proper rig tuning is the correct relationship
between mast bend and headstay tension
to get fast shapes. The North inventory has
been designed to make these transitions
easily with the correct tuning to be fast in
all conditions.
Step One: Check Mast Butt Position
The measurement from the front of the
forward bulkhead to the aft face of the
mast should be 24.46cm (9 5/8”). This is
very close to the center of the step. For
the HA sails, the mast butt should be
26.00cm (10 1/4”) from the bulkhead.
Step Two: Check J Measurement
The J measurement is the distance from
the headstay intersection to the deck to
the forward face of the mast. This should
be a minimum of 4.11m (13’6”). Use mast
chocks or SparTite to achieve this position.
lean over to leeward, increasing sheeting
angle. In light and moderate air, the jib will
sheet tighter to the centerline if you lead
the sheet straight to the winch from the
jib lead block. In heavy air, it can be faster
to use the turning block to sheet the jib
outboard slightly.
Step Three: Set Mast Rake
Rake is controlled by headstay length. The
headstay should be set at the class legal
maximum rake, 13.035m (42’ 9.125”). Hoist
a crewmember up the mast and have
them hold the butt of the tape measure
at the center of the pin that secures the
forestay to the mast. Measure to the
to of the furler drum (measurement
A), then measure from the top of the
furler drum to the bottom of the furler
drum (measurement B), then from the
underside of the furler drum to the
intersection of the stem and sheer line of
the boat (measurement C). The overall
headstay measurement is then the sum
of A+B+C.
Step Four: Centering the Spar
Put a mark on the rail of the boat on
one side even with the chainplates.
Measure this distance from the
headstay attachment on the bow. Put a
corresponding mark on the other side, the
same distance from the headstay. At this
point the Upper Shrouds (Caps) should
be hand tight and the Intermediates (D2s)
and the Lowers (D1s) should be loose.
Hoist the tape measure to the top on
the centerline jib halyard. Measure to the
Fig. 5: Measurement locations for
setting the mast rake
Fig. 6: The J measurement should
be a minimum of 4.14m (13’ 7”).
Fig. 7: Measuring Rig Tension
with the RT-10m Gauge
Fig. 5 Fig. 6 Fig. 7
Stem Line
Furling Drum
Sheer Line
C
B
A
Stemhead Fitting
Center of pin at forestay
fixing point of the mast

6
J/105 Tuning Guide Solutions for today’s sailors
marks on either side and adjust the Caps
until they are equal.
Step Five: Tensioning the Shrouds
Tighten the D2s and D1s to hand tight.
Add 8 full turns to the Caps. Then tighten
the D2s 6 turns. This should be done
incrementally (2-3 turns at a time per side)
sighting the mast to be sure that the mast
is in column. Add turns to one side and
remove turns from the other to bring the
mast in column. This added tension that
you have applied has probably made the
D1s slack, so double check to make sure
that they are hand tight.
Step Six: Check Shroud Tensions with
Loos Gauge
Put marks on the shrouds 2m (6’ 6 3/4”)
up from the deck. Put the top post of
the gauge on this mark when measuring
tension. Be sure to have the backstay
released when measuring tension with
the Loos Gauge. For the base setting for
10-14 knots TWS the shrouds should read
the following:
All Purpose Sails Heavy Air Sails
Caps: 35 55
D2s: 10 25
D1s: 0 (10 cm play) 10 (hand tight)
You should double check to be sure that
the mast is still in column at the dock
when the rig is at full tension. At the base
setting, the mast should sit with virtually
no pre-bend up to the hounds.
You are now at the “base” setting and ready
to go racing. From here follow the Quick
Tuning Guide to optimize your J/105’s
performance for various wind conditions.
Advanced Tuning – Beyond the Numbers
The North Sails J/105 Tuning Guide is
very refined, and has been used to the
letter to win many events. However,
understanding the fundamental concepts
of how tuning aects the rig and sails is
important to be able to check that the
settings are right for your boat, as well as
customizing your own tuning numbers for
your sailing style. Keeping good records
is the key. Keep a Wet Notes pad on your
boat and record your rig settings, wind
speed, sea state, and your speed and
pointing relative to other boats. This will
help you to see what is working best for
you and fine tune your own numbers.
Changes to shroud tension aect the
rig in two ways: 1) headstay tension & 2)
mast bend. Tighter Cap shrouds generate
more headstay tension by pulling back
against the headstay. A good guide for
Cap (upper) shroud tension is that the
leeward Cap shroud should just go slack
in all but the heaviest of wind conditions.
Tighter D1 (lower) and D2 (intermediate)
shrouds generate more headstay tension
by reducing mast bend and compression.
The important factor of the D1 anD2
adjustment is the relationship to the
amount of backstay used in each wind
condition, which aects mainsail shape.
Tight D1s and D2s will make the mast too
straight (main too full and draft forward)
when no backstay is used, and conversely
loose D1s and D2s will allow the mast
to bend too much (main too flat or even
inverted) when a lot of backstay is used.
The final D1 and D2 rig tension will be
dictated by mainsail shape.
The light air performance of the J/105 can
be dramatically improved with leeward
mast sag in under 12 knots. This is side-to-
side sag from the partners to the hounds.
This can only be seen under sail and will not
happen at the dock. The settings from the
Quick Tuning Guide should generate this
sag, but all masts are a little dierent, so
you may need to adjust your intermediates
and lowers to achieve it. Loosen the
intermediates and lowers so that there is
2.5cm (1”) of leeward sag halfway to the

7
J/105 Tuning Guide Solutions for today’s sailors
hounds in under 9 knots and Zero in 9-12
knots. In general the intermediates will
need to be eased twice as many turns as
the lowers to achieve even sag.
Part 3: Mainsail Trim
The J/105 relies on much of it’s power
from the mainsail with the class inventory.
The mainsail is very easily adjusted
because there are many shape controls
including mainsheet, traveler, backstay,
cunningham, vang and outhaul. Proper
mainsail trim is achieved by balancing
the speed and pointing with its twist,
angle of attack and overall power. Proper
communication with the helmsman for
the feel of the boat and performance
vs. the boats around you are the key to
establishing the correct balance of those
three elements.
Mainsail Angle of Attack — The Traveler
The traveler controls the boom angle
to the centerline of the boat, which is
described as angle of attack to the wind.
Much like the sheet, a narrow angle of
attack (traveler high) is used for pointing
and powering up the boat and a wide
angle of attack (low traveler) is used for
acceleration and depowering the boat.
Carry the traveler as high as possible
without making the boat heel too much.
In light to moderate conditions the
boom should be on centerline or slightly
above. In very light air, when the main is
twisted, setting the boom actually above
centerline will put the lower third of the
main parallel to the centerline of the boat.
A good gauge for this is to look where the
bottom batten is pointing. The bottom
batten should point at the backstay in
very light air. If it is pointing to windward
of the backstay, the traveler is too high.
As the breeze builds, the traveler should
be played aggressively to control heel and
keep the boat on its feet. If the boat heels
too much, the boat will get too much
helm and the helmsman will have to use
much rudder angle to keep the boat going
straight. The optimum rudder angle to
create the most lift is around 4 degrees.
There are times when more angle than
that is unavoidable, but 5 degrees of
rudder angle should be the most that you
try to use. Rudder angle can be monitored
by putting a tape mark on the top of
the wheel when it is perfectly straight.
The main trimmer can notice when the
helmsman is using too much helm (or
not enough) and adjust the traveler
appropriately.
Mainsheet vs. Traveler for Various
Sea States
One of the more dicult things to
determine is how to depower the main
in moderate to heavy conditions. As we
have learned, you can depower the main
by either twisting the main by easing the
sheet or letting the traveler down. The
technique used should be determined
by sea state, which will aect how the
helmsman has to steer the boat. In flat
water, the helmsman should be able to
use very subtle steering changes. Hours of
on-the-water testing has shown us that
depowering by lowering the traveler and
keeping a tight, untwisted leech produces
the best VMG. You can point reasonably
high in flat water without slowing down
and the tight leech will help with pointing.
We have found that twisting the main in
flat water in moderate air only makes you
lose height. With this style the traveler is
played to maintain the proper angle of heel.
However in waves and chop, the opposite
has proven to be faster. In waves and chop
the helmsman has to be more aggressive
with the helm. With the wider range
of steering keeping the traveler higher
(with the car near centerline) with a more
twisted main allows the helmsman to steer
through wider angles and accelerate as
needed in the waves. With this style the
mainsheet fine tune is played to maintain
the correct trim and angle of heel as the
helmsman steers through the waves.
Fig. 8
Fig. 8: Perfect Trim in 7 TWS

8
J/105 Tuning Guide Solutions for today’s sailors
Overall Power – The Backstay
The backstay is the most important sail
control for setting the overall power of
the sail plan. The backstay is the universal
control to modify the shape of the main
primarily, but also the jib. The North Class
Inventory has been carefully designed
so that backstay adjustment changes
the shape of the main and jib in unison.
As backstay is applied the mast bends,
flattening the main. It also pulls aft against
the headstay, reducing headstay sag,
which flattens the jib. By flattening the
sails the boat’s power is reduced as the
boat becomes overpowered and heels too
much. Flatter sails can be trimmed harder
than full sails so when it is windy it is better
to set the sails up flatter and sail with less
twist. This will allow you to point higher.
As stated in the tuning section of this
guide, having the rig set up properly for
the wind conditions will allow you to get
the most benefit of adjusting the main
and jib together with the backstay, but it
is also the control that allows you to set
up the sails as best you can when the
wind changes and you are no longer
tuned correctly.
With a loose rig the main will flatten out
faster than the jib. This is because the
loose D1s and D2s will allow the mast
to bend, which will flatten the main.
However, since the mast is bending, the
main will get to a point where it over
bends before you can bottom out the
backstay. By not being able to bottom
out the backstay, the jib will still be a bit
fuller than is ideal at this point since 1) you
can’t pull on the full range of backstay and
2) the mast will compress more so the
backstay tension will not transfer as well
to the headstay.
Conversely, with a tight rig, the main will
stay fuller when the backstay is eased,
while the overall rig tension will keep the
headstay tighter and thus keep the jib a
bit flatter. It is important to understand
this relationship between how the
backstay and rig tuning aects sail shape
when you may not be tuned correctly. If
your rig is too loose, use more backstay to
set the main up flatter, knowing that your
jib will be fuller than ideal. If your rig is too
tight, use less backstay to set the main up
fuller, knowing that your jib will be flatter
than ideal. In general, it is better to be set
up with a flat main and a full jib so it is
better to err on the loose side of the rig
tuning matrix if you expect the wind to
change. It’s much easier to depower the
J/105 than it is to power it up so always
tune for the lulls!
As the mast bends it has an immediate
eect on the lu and leech tension,
so other controls must be adjusted in
conjunction with the backstay. When
you pull the backstay on, the mainsail
will twist more so more sheet will have
to pulled on to reset the twist. More
backstay will also loosen the lu, so more
cunningham will be needed. Don’t forget
to ease the sheet and the cunningham
after you ease the backstay.
Other Mainsail Controls
Cunningham
he cunningham controls the lu tension
of the mainsail. Lu tension controls the
draft position of the mainsail. As backstay
tension is applied, the mast compresses
and the main appears to fall down a little
and the draft will move aft. Pull on the
cunningham to move the draft forward
to the desired position. As well as moving
the draft, lu tension will also make the
main somewhat flatter. In light air, you
should see slight wrinkles coming from
the sail slides. In moderate air the lu
should be smooth. In heavy air, the lu
should be tensioned past being smooth to
set the draft position and flatten the sail.
Vang
With the non-overlapping jib, in order for
the mainsail to generate enough power
in light air, a certain amount of depth has
Fig. 9: Light Air Upwind –
Traveler is high, boom is slightly
above centerline. Crew is low and
forward. The boat is balanced
nicely with a good heel angle.
Fig. 10: Nice heavy air upwind
form here. The traveler car is
centered and speed is being
controlled with the mainsheet
fine tune.
Fig. 9
Fig. 10

9
J/105 Tuning Guide Solutions for today’s sailors
been designed into the lower portion. In
over 12 knots begin to pull on the vang to
induce low mast bend to flatten the lower
third of the main. When it is really windy
pull on the vang quite hard to help bend
the mast. be sure to ease the vang at the
weather mark! Before you ease the main,
ease the vang to allow the main to twist
as you bear o. If the vang stays on too
hard, you may not be able to bear away, or
worse you could break the boom.
Outhaul
The outhaul also controls the sail shape
in the lower third of the mainsail. Easing
the outhall makes the lower third of the
mainsail fuller and tightening flattens the
lower third. In light air the outhaul should
be slightly eased and pull it progressively
harder as the wind increases, to the point
where you should pull it as hard as you
can in over 15 knots.
Part 4: Jib Trim
The J/105 Class Jib has a very tough job. It
has to be fast in all wind conditions, where
other 35’ oshore one-designs allow
three headsails! The single jib inventory
presents a tough challenge for sail
designers to create a sail that is versatile
enough to cover the entire wind range,
while being constructed so that it can be
light enough to perform well in light air,
yet being strong enough to handle heavy
air. The 3DL jib is the ultimate solution
to handle this daunting task. The latest
design has been refined to be responsive
to the few controls that can change the
shape. The 3DL process is the only way to
create a sail that is minimum weight, yet is
strong enough for heavy air.
While the North 3DL jib is refined to a level
that makes it very easy to enhance the
light shape in light air and a heavy shape in
heavy air, it is important for the trimmer to
be able to manipulate the sail appropriately.
The primary controls that we have to aect
the sail shape are the halyard, sheet, jib lead
placement and headstay tension.
Jib Halyard
The halyard is the most important sail
control for shaping the jib and it has a
much greater aect on sail shape than
the cunningham on the main. However,
just like the cunningham on the mainsail,
the halyard controls the entry angle, draft
position, and overall depth in the sail. A
tighter halyard will produce a more draft
forward, rounded entry shape, with less
overall depth. A loose halyard will produce
a more draft aft, finer entry shape with
more overall depth. As a general rule, the
halyard should be tensioned to just barely
remove the wrinkles in the lu. In lighter
air wrinkles can just be visible, in moderate
air the lu should be smooth, and in heavy
air the halyard should be pulled 2.54-
7.62cm (1-3”) past removing the wrinkles.
In flat water, a looser halyard can improve
pointing with a finer entry angle. In waves
and chop, a tighter halyard will produce a
more rounded entry and more open leech,
which will have a wider steering groove
and be better for acceleration. If you try
the loose halyard and your helmsman
seems to be struggling to find the groove,
try a slightly tighter halyard.
As sails age, the entry tends to get finer
and the draft starts to move aft. An older
sail will require more halyard tension to
achieve the same shape as a brand new
sail with a looser halyard.
Jib Sheet
The sheet is the most important control
for adjusting the jib once the draft is
set. The general rule is to trim the jib as
hard as possible without slowing the
boat down too much. The jib needs to
be played in conjunction with the main
and the helmsman’s steering. The sheet
tension will change with each change
in the wind speed. When a pu hits, the
leech will become more open. Be careful
not to trim the jib too soon. Allow the
leech to stay open to take advantage of
the pu to accelerate the boat and them
Fig. 11: Median Jib Lead Position
In light air, move the lead forward
up to 3 holes so that the jib foot
is close to touching the lifelines.
In heavy air, move the lead aft up
to 2 holes to make the foot flat.
Fig. 11

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 dierence.
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 aected
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
aect on the overall camber of the jib.
Headstay tension aects headstay sag.
This is a dicult thing to visualize, but
it works much the same as mast bend
aects mainsail shape. As the headstay
sags, it pushes the lu towards the leech,
which increases camber. Conversely as the
headstay gets tight, it pulls the lu 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 aect 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.

11
J/105 Tuning Guide Solutions for today’s sailors
Light Air
In light air the crew should be well forward
and to leeward both upwind and down.
Two crewmembers should be forward of
the shrouds to leeward. Remaining crew
should be up near the shrouds. There
should only be one person in the cockpit
other than the helmsman. In really light
air the main is not trimmed that often
and the helmsman can make small
adjustments. Being to leeward helps heel
the boat increasing helm giving a better
feel and allows for the best pointing and
rudder lift. Being forward allows the bow
to dig in which also helps pointing as well
as reduces wetted surface by getting the
transom out of the water.
Moderate Air
In moderate air the crew can begin to slide
back as they begin to move to weather.
Once anyone goes to weather they should
be stacked just behind the shrouds. At
this point if you have a dedicated main
trimmer, he can slide back to his station
upwind. Downwind as soon as there is
constant adequate pressure on the sheet
and you begin to try to sail low the crew
should move to weather to help rotate the
spinnaker to windward out from behind
the main. This happens at about 10 knots.
There is plenty more coming on downwind
sailing in Part 6, starting on page 21.
Heavy Air
In heavy air the crew should continue to
move aft, especially in waves. If you notice
that your helmsman has to steer a lot to
keep the boat going straight (dialing for
dollars), move aft and as the bow lifts the
boat will track straighter. Since crew weight
is limited the guys who are on the rail need
to hike hard. Remember, sailing is a sport
and it’s a boat not a couch!
Part 6: Downwind Sailing
Sailing the J/105 downwind can be one of
the more dicult things to do well. Paying
small attention to the minor details can
make a huge dierence. The key to fast
sailing downwind is good communication
between the trimmer and the helmsman.
The trimmer should constantly be telling
the helmsman how much pressure he has
in the sheet. This will allow the helmsman
to know if he can bear o a little more, but
more importantly when he needs to head
up a little bit to build pressure.
The J/105 has an asymmetric spinnaker set
on a centerline sprit. The goal in downwind
sailing is to maximize downwind VMG. This
is achieved by sailing a wind angle tight
enough to keep speed, but sailing lower
towards the mark whenever possible. The
North Sails asymmetric has been designed
as a running spinnaker for optimum
downwind performance at the apparent
wind angles that produce the best VMG
for the J/105. The sail has been designed
to rotate out to windward to project the
maximum sail area out from behind the
mainsail. Always hoist the sail all the way to
the top. Due to the lu length restriction in
the rules, the tack of the sail is never set all
the way down to the pole. Raising the tack
helps the sail to rotate to windward.
Light Air Sailing (0-9 knots TWS)
In light air, you must sail tighter angles for
best VMG. The tack is set 0.3m-0.6m (1-2’)
o the sprit. The crew should be forward
and to leeward. Keep the crew weight as
low as possible. Steer down in the pus
until the pressure sheet starts to get light
and then head up slightly. Communication
between the trimmer and the helmsman is
key. Try to find the lowest angle you can sail
before the speed drops. Don’t forget about
the main! Proper mainsail trim is essential
to good speed. The vang should be set so
that the top batten is open by 5 degrees. A
good trick to help acceleration out of the
jibes is for the main trimmer to hold the sail
in a bit after coming out of the jibe. When
the asymmetric is jibed, it needs to
be overtrimmed to make it “pop” through.
When the spinnaker is overtrimmed, it
blows air back into the mainsail relieving
pressure from it. By keeping the main in,

12
J/105 Tuning Guide Solutions for today’s sailors
it will keep the main pressurized as well
as opening the slot between it and the
spinnaker to get the air flowing over it
faster. The main trimmer can easily feel
if the main is pressurized by the pull on
the sheet. Ease the main out slowly as
the pressure on the sheet builds as the
spinnaker is eased.
Moderate Air Sailing (9-12 knots TWS)
In moderate air, there is a wide range
where you can sail. Lower is best as long
as you can maintain your speed. The tack
line is eased 0.6-0.9 (2-3’) o the sprit. The
same principles apply to steering as in light
air. Once the boat feels well pressured, the
crew should move to the windward side
to help rotate the spinnaker. In this range
the crew should be very active moving to
weather when you head down in the pus
and back to leeward when you head up in
the lulls.
Heavy Air Sailing (12+ knots TWS)
In over 12 knots, the boat is well pressured
up going downwind. At this point you want
to sail as low as possible most of the time.
There will almost always be good pressure
on the sheet but when you sail too low,
the sail will become blanketed behind the
main and collapse. The sheet is well eased
to get as much of the sail out from behind
the main as possible. The crew should be
to windward at all times. Heel the boat to
windward by as much as 10 degrees. The
vang should be set so the top batten is
parallel to the boom.
DOWNWIND NOTES
Good coordination between the trimmer
and helmsman will result in very
subtle changes in the sheet. A properly
coordinated team will only adjust the sheet
by a couple of feet. If you find yourself
constantly trimming and easing more
than 3 feet of sheet than your coordination
should be improved. Be careful not to try to
sail too low and collapse the spinnaker. A
collapse will result in around a three-boat
length loss!

13
J/105 Tuning Guide Solutions for today’s sailors
All Purpose Sail Adjustments (All full turns from BASE settings)
Heavy Air Sail Adjustments (All full turns from BASE settings)
TWS
Light Winds (0-6 kts)
Light/Medium Winds (6-10 kts)
Medium Winds (10-14 kts)
Medium/Heavy Winds (14-18 kts)
Heavy Winds (18+ kts)
TWS
Light Winds (0-6 kts)
Medium Winds (10-14 kts)
Heavy Winds (18+ kts)
V1 (Caps)
-1.5 turn
-1 turn
BASE (35-RT10 Gauge)
+1.5 turn
+3 turn
V1 (Caps)
40 (-3 Turns)
BASE (55-RT10 Gauge)
65 (+5 Turns)
D1 (Intermediates)
-3 turn
-1.5 turn
BASE (10-RT10 Gauge)
+2 turn
+4 turns
D1 (Intermediates)
10 (-5 Turns)
BASE (25-RT10 Gauge)
35 (+5 Turns)
D2 (Lowers)
-2 Turns
-1 Turns
BASE (0-RT10 Gauge)
+1 Turns
+2 Turns
D2 (Lowers)
10cm of play (-1.5 Turns)
BASE (Hand Tight)
Slightly Loosed (+1 Turn)
J 105 Tuning Guide

14
J/105 Tuning Guide Solutions for today’s sailors
Worldwide Service
At North Sails, we view each sail purchase
as the beginning of a long and rewarding
relationship. We base this expectation on a
strong service commitment that includes
preventive maintenance, sound advice,
education and expert repairs.
North Sails is a network of more than 100
lofts in 34 countries around the world. Each
oers knowledgeable, friendly, personal
sales and service. Our size and worldwide
reach also means North has the world’s
most expansive sailmaking database. It
would be hard to find a sailboat for which
we cannot make a fast, durable and long
lasting sail.
All North Lofts oer:
• Annual checkover
• Winter storage
• Retrofitting
• Educational
• Sail washing
• Sail tune-up
• Seminar resources

J/105 Tuning Guide Solutions for today’s sailors
The North Promise
North Sails proudly stands by
every product it makes. Our
years of innovation, research and
testing make us confident in the
high quality of our products.
This is why with every Cruising,
Racing or One Design sail we
oer free sail care and repair,
honoured anywhere in the
world through our network of
service locations.
Terms & conditions apply
For more information visit
the North Sails Oshore One
Design website at:
oshoreonedesign.com
For any question you may have
on tuning your J/105 for speed,
contact our experts:
Skip Diebal
[email protected]
419.392.4411
Jack Orr
[email protected]
203.877.7621
For other useful information
visit the J/105 class website
j105.org