tufts, indicators, flappers, woollies - a dear
child has many names. No matter what you call
them, they are an essential aid in steering and
telltales make the trimming of the sails and the steering
of the boat easier. You shouldn't stick too many telltales
on your sails - when sailing, the amount of information
streaming in exceeds the capacity of the crew, so keep
it as simple as possible. In this article we explain
which telltales are essential and sufficient at the
same time. We recommend not to have more telltales than
that. The telltales in the leech should be made of a
rather strong nylon strip. Normally they are already
installed by your sailmaker. The telltales in the luff
should be of woolen yarn glued onto the sail with a
the mainsail telltales are only needed in the leech.
Cut them out of an inch wide nylon strip and sew them
into the ends of the batten pockets. The right length
is from six to twelve inches. On the race course colorful
strips are the best but if you are racing at night,
you are better off using white telltales because they
show clearly against the dark sky. That's why the telltales
on offshore racers often are white.
telltales near the luff of the sail are used as a steering
aid when sailing upwind. If you are pointing too high
the windward telltales "stall", i.e. point straight
up or stream forwards or twirl around restlessly. If
you are sailing too low the leeward telltales hang down
and die, which is a sign of a serious steering error
- the leeward telltales should always stream steadily
aft. When the leeward telltales stall, the jib trimmer
should ease the sheet until the helmsman is back onto
his proper course again. Stalling the leeward telltales
means that the whole foresail is about to stall. It
then loses most of its drive and only the heeling force
windward telltales indicate different things depending
of the wind strength. In light winds your heading is
correct when both the windward and leeward telltales
stream steadily aft. The maximum speed is achieved by
steering so high that the windward telltales are just
about to twirl. In medium winds the best speed is achieved
when the windward telltales jump up at steady intervals.
Telltale 1, telltale 2, telltale 3 - jump - telltale
the wind increases the telltales become less important
as an indicator of the proper course. Steer the boat
according to the heeling angle and the wave conditions
and never mind the (windward) telltales.
steering telltales are most useful when sailing upwind.
Steering according to the telltales in light and medium
conditions normally maximizes VMG, i.e. your speed towards
the mark is the greatest. A high VMG does not necessarily
mean the highest speedometer values, but indicates the
ideal combination of boat speed, pointing and leeway.
the main and the jib should have two to four telltales
in the leech, used to proper sheeting. The leech tails,
as well as the telltales for steering, are of the most
value in light to medium air. The telltale at the end
of the top batten pocket is essential when adjusting
the proper twist for the main sail. When the telltale
disappears behind the sail, the sheet is too tight and
the sail has too little twist. In a light winds (5 to
10 kn) the top telltale should be flying for about half
of the time. In less than about five knots the leech
tails won't work properly. When the wind picks up, the
sail is flattened and all the telltales normally stream
two telltales below the top one tell us about the overall
shape of the sail. When the top telltale streams steadily
aft but the second one is stalling, your main is either
too full in the middle and /or too flat in the top.
Bending the mid-section of the mast normally helps.
The stalling of the lower telltales may also indicate
that your jib is sheeted too loosely, and causes the
airflow to separate on the leeward side of the main.
Closing the gap by moving the jib lead forward/inward
or changing into a larger genoa will help.
main sheet is the most important trimming device on
your boat, and the top leech tail is the best indicator
of the main sheet tension. The required tension on the
main sheet depends of the boat you have; use the top
leech tail when you are looking for the right trim in
different condition. In less than 5 knots of wind adjust
the sheet so that the upper tail is visible only sometimes.
In medium air the upper tail should show itself about
50% of the time, and in heavy air all leech tails must
telltales in the leech of the genoa behave somewhat
differently from the ones in the main. Never sheet your
genoa so tight that all the telltales in the leech stall!
Before stalling, the telltales become slow and lazy;
that indicates your maximum trim. However, if your boat
has a high & narrow jib, with little overlap (like
on some one-designs), you may allow the leech tails
to stall from time to time in a light air and medium
airs. The top telltale is again the most important as
it is usually the first one to react to the wrong trim.
In some boats the spreaders restrict how far in the
genoa can come. In these boats the top telltale may
still stream aft when the middle one already stalls
- ease the sheet a hair. In older jibs the leech may
start to hook in and the telltales become then less
Sticking tails on headsails
the telltales at the half and quarter points down the
leech. Two pairs of steering telltales should be installed
in the luff of the sail approximately ten to twenty
inches behind the luff rope *) and four to eight feet
above the tack. In small boats the telltales should
be lower and nearer to the luff than in bigger boats.
Don't set the telltales at the same spot on different
sides of the sail but always fix the starboard telltale
an inch higher. When sailing towards the sun it may
otherwise be difficult to distinguish the windward telltale
from the leeward one. If you happen to forget which
telltale is higher look at the mainsail numbers; they
follow the same rule.
a good idea to have two sets of steering telltales.
One set should be installed a bit higher and closer
to the luff than the other. The telltales further away
from the luff are more forgiving and you should steer
according to them in rough seas and in heavy winds.
The telltales closer to the luff are more sensitive
and you should use them in smooth seas and lighter conditions.
telltales get easily stuck - avoid installing them too
close to the seams. If the lower telltales have got
stuck, or if the crew is obscuring the view, you can
steer by the upper set. The telltales shouldn't be installed
higher than where you can reach from the foredeck, so
that you can easily free them in case they get stuck.
One way to release a telltale is to smack the clew -
this helps to avoid the unnecessary trips to the foredeck.
top telltale set is to be installed nearer to the luff
than the steering telltales. They are mainly used when
determining the right amount of twist for the jib on
The correct distance from the luff depends on the sail
size: stick your driving tales at a distance of 7,5-15%
of the width of the sail at the level of the telltails.
a reach ...
telltales are used for trimming the sails. The helmsman
steers by the compass or to a fixed point in the horizon
and it is the crew's duty to keep trimming the sails
so that the telltales stream steadily aft. On a reach
the top telltales in a jib are of good value when determining
the right twist, which is otherwise very difficult,
especially with high aspect ratio jibs. If the windward
top telltales are stalling, move the jib lead forward.
Remember that you can rely on the telltales only in
light and medium conditions. In strong winds the heel
becomes the main trimming indicator and the excess power
has to be released by increasing the twist. The jib
trim on a reach is always a compromise between the upper
and lower sections of the sail. It might be a good idea
to move the jib lead all the way out to the toe rail
and forward so that the windward top telltale streams
steadily aft. Normally it is very difficult to get both
the top and bottom telltales to work well together.
top telltales also give an indication of the sag of
the headstay. If the windward telltale wobbles all the
time, the top section of the sail may be too full; try
straightening the headstay. However, it is quite normal
that the windward tail streams right up when it gets
windy and you are overpowered.
use the luff telltales when looking for the right position
for the jib lead - the information you get is often
more harmful than beneficial. You may have the lead
way back but the sheet very tight, and the telltales
be streaming fine, or vice versa. The correct jib trim
is always a combination of lead position and sheet tension,
and there is no single right lead position.
make trimming and steering easier. One should not, however,
stare his eyes out at them. If the cut of your jib is
too flat, you will achieve the best speed by steering
the boat so low that the leeward telltales are partly
stalling. You should try to make the jib fuller by letting
the head stay sag a bit. On the other hand, if your jib
is too full (which inevitably happens to all sails at
some stage when the wind picks up) you should steer the
boat so that the windward telltales are twirling up. In
strong winds, let the telltales live their own lives and
steer the boat according to heel and sea conditions.
If the leeward telltales are stalling or streaming
forward, you are sailing too low. Come up a bit,
or ease the jib sheet. bit, or ease the jib sheet.
In light air, steer just on the verge of collapsing
the leeward tails.
If the windward telltales are continuously jumping
up but the boat isn't heeling excessively, you are
sailing too high. In medium air on an ideal heading
the telltales jump up at three to four second intervals.
stronger winds (15 kn +) ignore the telltales
and steer by the heel angle.
separation & boundary layers
the wind sweeps past the sail its velocity near the
sail surface decreases because of the friction. This
so called boundary layer can be over 2 inches
thick in the middle on the windward side and in the
leech on the leeward side of the sail. When the velocity
of the air stream decreases to a certain point the
boundary layer separates from the sail. The telltales
indicate how the boundary layer is behaving at different
moments in different parts of the sail. The separation
of the boundary layer always means a significant loss
in power and is to be avoided at all cost. This is why
the telltales are so useful, and why we try to trim
the sail so that they always stream steadily aft.
sail is often compared to a wing of an airplane. A sail,
however, has one aerodynamic characteristic that makes
the comparison feeble. In the luff of a sail the airflow
always gets separated from the sail surface on one side
or the other, creating a separation bubble. The thick
and round leading edge of a wing - or a keel of a sailboat
- eliminates the separation of the boundary layer, which
improves the efficiency of the foil considerably.
the airflow meets the luff of the sail in too
steep an angle, it separates and a separation
bubble forms. The bubble is like a small eddy
where air circulates around in the same spot.
The tighter the sail is sheeted the longer the
separation bubble will be. The airflow reattaches
to the sail behind the separation bubble. Depending
on the size of the bubble and the position of
the steering telltales they either stream steadily
aft, twirl in a funny way or in the worst case
even stream forwards against the wind.
you are pointing too high the bubble forms on
the windward side of the sail. The bubble on the
windward side is less harmful than the one on
the leeward side; in heavy winds there is always
a bubble of some length on the windward side of
very luff of the sail nearly always has a separation
bubble on one side or the other which is why the
telltales shouldn't be installed too close to
the luff. When the sail is sheeted properly and
the boat is on its ideal course, the telltales
on both sides of the sail stream steadily aft.
this case, the separation bubble at the luff is
then extremely small and alternates from one side
to the other. The airflow meets the luff of the
sail at an ideal angle and the flow is smooth
at both sides of the sail.
you are sailing too low, or if the sail is sheeted
in too hard, a separation bubble forms on the
leeward side. This is very harmul to the performance
and should be avoided at all times.
of the luff separation bubble, the airflow may
get detached from the sail just before the leech
on the leeward side. The eddy formed like this
makes the leech telltale disappear behind the
sail. For the sake of clarity, the size of the
separation bubbles is exaggerated in the drawing.
graph on the left represents the forward force or the
driving force at different apparent wind angles for
a 40-footer in a light wind (AWS = 12 kn).
driving force increases steeply until the apparent wind
angle is 21¡. Until then there is a separation
bubble on the windward side of the sail, which gradually
disappears. The windward telltale wobbles or streams
upwards and the luff of the main may backwind. The 22¡
apparent wind angle is optimal for this setting of the
sails; both telltales are streaming steadily aft. This
is when the driving force in relation to the heeling
force is at its maximum. When bearing off further the
driving force still increases, but less steeply than
earlier. The airflow starts to get detached more and
more on the leeward side of the sail, as shown by the
stalling of the leeward telltales.
this computer simulation only the course the boat sailed
is altered while the sheeting of the sails remain the
same. In a real situation the sheeting of the sails
would be adjusted according to the course.
© 1995 -98 WB-Sails Ltd. Updated 7/98. All rights