Look for Changes in Wind
by David Dellenbaugh
One thing you can say for sure about the wind direction is that it’s always
changing. Even when it seems like a nice steady day, the wind is constantly
wriggling back and forth at least a little bit. And whenever the wind
shifts, it creates a large opportunity to gain distance on the other boats
in your fleet.
|Why shifts are critical
|Size of wind shift
|Distance (approx.) gained or lost
5% of x
12% of x
25% of x
37% of x
Wind shifts are generally the most significant strategic factor of all. Each
time the wind changes direction it re-shuffles the fleet standings, and in
almost every race the potential gains and losses due to wind shifts are
greater than any other factor, including boatspeed!
|One common cause of changes in the wind direction is the
presence of land near the race course. The wind encounters more friction
when it flows over the bumpy contours of land, and this often affects
its direction. The degree of change is influenced by your proximity to
shore (the closer you are, the bigger the shift) and by the angle of the
wind to the shoreline.
For all these reasons, it’s very important to understand what the wind is
doing - both before and during your race - and how best to use the wind to
|Sail toward the next shift.
When the wind direction is changing, your basic strategic move upwind is
to sail in the direction where you expect the wind to shift next. For
example, if you think the wind will veer (shift clockwise), sail on port
tack toward that shift (and vice versa).
By doing this you will end up on a higher “ladder rung” when the wind
shifts, and therefore you will be more advanced in the race. Of course,
there could always be reasons (e.g. current, wind pressure) when it
might pay to sail away from the next shift.
• Many windward legs are only 10 or 20 minutes long so general, large-scale
forecasts (like the ones you get on the web, radio or TV) are not very
helpful. It is much, much more important to rely on:
- Local knowledge: In the specific venue where you are racing, what
does the wind usually do when it blows from each direction? Use your own
experience from past regattas and ask local sailors to tell you what
- Your own observations: These are even more important than ‘local
knowledge’ because they apply to your race area on the specific day when you
are racing. Be sure to collect these before the start, and keep observing
during the race.
When the wind is blowing from the land at an angle to the shoreline, it
tends to shift in direction so it flows more perpendicularly off the
land. This effect is more pronounced as you get closer to shore.
Usually, if you sail the tack that takes you more directly toward land,
you will get progressively headed as you approach the shore. This
“geographic shift” is like a basic persistent windshift, but it is
easier to predict because it usually happens in the same place and to
the same degree (so be sure to check this out before your race).
If the wind is blowing straight off the shore, it will act like an
oscillating breeze, so look for more frequent and substantial
back-and-forth shifts closer to land.
• There are many reasons why the wind changes direction. These include the
movement of weather systems, thermal heating, changing current, clouds and
geographic effects. Keep your head out of the boat and try to understand
which of these apply to your particular situation - this will help you know
which way the wind will shift next.
• Sail toward the next shift! When you expect that the wind will
change direction (it happens every beat!), the key idea in your strategic
gameplan should be to sail in the direction of the next windshift.
• When making a strategic plan for your windward leg, the relative
importance of windshifts will depend on several factors:
- In light air, windshifts are less critical; wind pressure and current are
|The influence of clouds
Another reason why the wind changes direction is the presence and
movement of clouds. The bigger the cloud, the more potential there is
for associated windshifts. Usually, the wind on the downwind side of a
cloud ‘fans out’ in front of the cloud (and it’s stronger too).
Therefore, it’s usually good to sail toward clouds. For example, if
there is a big dark cloud coming down the left side of the beat, sail
that way because the cloud will probably shift the wind direction left
until it passes.
- The importance of windshifts is proportional to their size.
- Shifts are more critical on longer beats where the boats get more
separation (farther apart).
• Windshifts almost always fall into one of two categories - they are either
oscillating (shifting back and forth around a median direction) or
persistent (changing steadily in one direction). If you want strategic
success, you must constantly ask yourself one simple question during each
windward leg: Is the wind direction oscillating or persistent?
|When you are sailing in a thermal “sea breeze”, the wind direction
usually changes slowly as the temperature of the land increases or
decreases during the day. While the land heats up in late morning and
early afternoon, the breeze builds in strength and gradually shifts
(often to the right) toward the standard ‘seabreeze direction’ for that
venue. Then in the late afternoon, after the warmest part of the day,
the land starts cooling and the wind shifts back the other way
(decreasing in strength).
Thermal breezes are great examples of persistent shifts. However, as the
seabreeze develops it doesn’t always shift constantly in the expected
direction. As the graph above shows, there are often some small
oscillations as the wind settles in. While these shifts may not be
significant on a long beat, they can make a big difference strategically
to boats that usually sail short windward legs.
The way you answer this question will make a huge difference in how you play
the shifts. For example, if you think the wind is oscillating and you get
headed you should tack. But if you think the wind is shifting persistently,
you should keep sailing into the shift.
• Sometimes what appears to be a wind shift is really a change in wind
velocity, not in its direction. If you are sailing along and the wind
velocity suddenly drops (without changing direction), your apparent wind
will shift forward temporarily and it will seem like you’re headed.
Be careful not to treat this “velocity shift” like a real change in
direction. If you suspect a change in velocity, wait 30 seconds or so and
see if the ‘velocity shift’ disappears once your boatspeed adjusts to the
new wind velocity.
• Windshifts are different every day. Sometimes it’s very easy to see them
on the water; other times it’s impossible. Sometimes when a shift hits your
boat it is solid right away; other times you have to sail farther into the
shift to make sure it’s real.
When you are trying to make a gameplan to take advantage of the shifts,
there is nothing as valuable as sailing around in your race area before the
start, just watching (and recording) what the wind is doing.
Dave publishes the newsletter Speed & Smarts. For a subscription call:
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