OSCILLATING SHIFTS
The wind direction sometimes oscillates about an approximate mean value. While sailing up-
wind, these shifts seem to occur more frequently to a fast boat. When sailing in such oscillating
shifts, you should always tack in order to be on the lifting tack. This will give you the straightest
possible course towards the windward mark.
If the wind veers, tack to starboard to let the wind come in from that side.
If the wind backs (swings to the left), you should let it come in from the left by tacking to port.
In figure
3
, the boat in the example has a tacking angle of 90° and the average wind direction is
supposed to be 000°. The boat starts by beating on port tack and is gradually lifted by the backing
wind. But then the wind starts to veer and eventually passes the average wind direction. Believing
that the wind will continue to veer, the helmsman tacks to starboard as the average wind direc-
tion is passed. He then is lifted up to 15° by the veering wind. Here the wind starts to back again.
When passing the average wind direction, the helmsman tacks to port. He is then lifted on port
tack until he reads 30°, he is then lifted 15°. Then the wind starts to veer again.
If the wind oscillates between 200 and 230 degrees, tack as the wind goes past 215 degrees.
The corresponding reading on the scale is 180° on starboard and 230° on port tack. If you tack
as soon as the wind starts to swing back from the extremes, you will find yourself headed on
the first part of the new tack. So small shifts that do not pass the mean value shouldn’t be
tacked on. It is the average wind direction for the whole leg that counts.
Rule of thumb:
As reading goes above mean: Tack to port.
As it goes below mean: Tack to starboard.
However, small shifts that do pass the mean
wind direction shouldn’t be neglected although
they might be difficult to see. The difference
between being headed or lifted while beating
is almost one metre per degree wind shift, per
knot and minute sailed. This means that going
the wrong way in a five degree shift while
sailing at 5 knots for one minute would bring
you almost 20 metres behind a boat that went
the right way. It isn’t easy to make up for such
losses by trying to sail faster.
PERMANENT SHIFTS
The wind sometimes shifts without returning to its original direction, at least not for the
remainder of the windward leg.
In this example
6
, the wind is first oscillating
at about 200 degrees. A permanent shift makes
it veer to 240 degrees and here the oscillations
continue. Tactically, the oscillations could be
neglected in a case like this. Changing tacks
should only be considered when the wind di-
rection goes past its mean value for the whole
windward leg.
It is often difficult to predict permanent shifts. Sometimes they are caused by “wind bends”
over the coast line or by channelling between islands. They could also be caused by clouds,
the sea breeze coming in or appear for other, totally unpredictable reasons. Shifts caused by
topography should be sorted out from those within the wind so that you can anticipate what will
happen on the next windward leg.
Sail into the new wind when there is a permanent
shift. If the wind veers, tack to port. You will be
more and more headed. Then tack slightly before
arriving at the lay line. Now the veering wind
will lift you up to the mark (Boat A). Tacking the
opposite way does not pay off since you would
loose more while being headed on the second
tack than you could win by being lifted on the first
(Boat B).
7
Charts of wind shifts made by sailing
meteorologists during races show
that the wind directions often change
in very complex patterns. Oscilla-
tions are added to shifts caused by
the coast line, clouds or the tendency
of the sea breeze to veer with the sun
during the day.
Other racing compasses have to be adjusted before the start to set the estimated mean wind
direction. This can be difficult and as soon as this direction changes any substantial amount
the compass needs readjustment. It is an advantage if the variations of the wind direction can
be followed directly and conveniently while sailing. This gives a better idea of how the wind is
shifting and permits continuos reappraisal of the mean wind direction.
Art.no 37189-0101 (MN), 37189-0103 (ME), 37189-0105 (MS)
FULL VERSION MANUAL
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