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shift or not to shift…(part 2) |
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Last time I elaborated a little bit about the concept of
oscillating or persistent shifts. I've I've tried to make
clear that:
A) Knowledge of interaction between
continental systems and their development with the local
systems like; convection or seabreeze etc. will be a lot of
help anticipating the shift during the leg or race.
B) With this knowledge it's essential
to start looking at the signals from the clouds, wind, water
etc. These can tell you in "Real time" what's actually
happening.
Don't forget that in order to predict the weather there
is a lot of modelling and calculating done by computers. And a
scientific mathematical model to calculate the data measured
on millions of weather measurements all over the world is
still a model; "a desperate attempt to describe the real
world". And that's still a liability if it comes to instant
decision making on a local situation like a 50 square meter
environment in which the racing takes place.
So after
the observation we go to the analysis from the weather bureau
and try to make sense of what's going on "on the screen" and
on in "Real Time" on the course.
This time I will
try to show you how to start using the "knowledge from
meteorological and Real Time observations" into the decision
making in the boat.
As we know by now. It all starts at getting an idea on if
and how the gradient will develop over the day. Mostly a
surface analyses and a forecast on how the closest High
Pressure, Low Pressure or Frontal zone will develop, is enough
to get this idea. Then it's time to get some idea on how the
local system will interact with this.
Let's take an
example: We're racing in Medemblik (site for our phenomenal
event the Spa regatta). A low-pressure areas over the Queen's
Island (GBR that is) is moving away towards the northeast
usually comes with a sector west gradient wind which is
veering during the day. To present this graphically:
So if it's not completely overcast and both land and water
temperature have dropped significantly overnight there's a
good chance of thermal effects during the day, and interacting
with this veering gradient.
This will mean that at
from about 10 am we need to be alert for the increased
visibility (disappearance of the haze) plus a possible
development of small and relatively cumulus development as a
sign that morning convection can happen. If nothing weird is
happening (like the approach of a warm front) there's a good
change of gusts (patches of more and/or backed/or veered wind
between 10 secs and 3 min) with veered winds (sometimes up to
15 degr) with increased windspeeds (up to + 5 kts). This gusty
period can last between 15 min. up until 2 hours. Possibly a
seabreeze will establish afterwards.
So on the course
and during for instance an early race graphically it could
look like.
fig2.
 Let’s say we’ll have a starting time at
10:00 hrs. If we’re on our way to the racing area (and take
the laid back option of being towed out!!!), we can already
start to look at the way the wind is behaving. So how strong
is the main wind? Do I see any gusts on the water? How fast do
they move? Do they move with the main wind direction or do
they come from a particular side or from a different
direction? How is the direction of the wind at the edge of the
gust? And how in the middle? For instance from the right in
this particular case? How is the course oriented to the coast?
(“because that big flat area there could explain why there
always more gusts on the left side of the upwind…”) Once on
the course and after tuning your boat for the first upwind
conditions, you have to start checking the numbers (i.e. have
a look on the compass). Just sail full power away from the
starting vessel on starboard tack and check the compass
bearing, and keep on checking it over the next 3-5 minutes
while sailing full power on this tack. You will (hopefully)
find out that the numbers on the compass will increase during
the gust and decrease after the gust. Try to be very conscious
of how this all looks on the course oriented to the topmark if
you’re lifted and what it all look like if you’re fully
headed. Do the same thing on port for a while. The more time
you’ll spent doing this the more you’ll get an idea on how it
looks without all the boats around and with the numbers on the
compass as a back up.
Fig3.
With the very good chance of convection present during the
first beat, keep an eye on the way the gusts change over time
and try to imagine what tactical situations will look like
during the race. For instance when this gusts is just about to
hit you while trying to fight off a group on you windward hip.
And same situation when the gust just passed.
With this
in mind you'll return to the starting area (in time!!) and
start your pre-start orientation and make your plan on where
to start and how to sail the first beat. After maybe four or
five times of this kind of race preparation you'll be more
aware of oscillations and persistent shifts and you'll
definitely get better races in.
Let's continue with
this example racing day.
Later, that day the wind will
predominantly consist out of the interaction between the
gradient and the seabreeze. The gusty period (convection) and
the onset of the seabreeze (a big lefter about 20 degree that
day) have all passed and took their toll during the races
before.
Than we get 16:00 hrs. Now at this time with
the dropping of the sun, it's possible to feel the intensity
of the sun dropping the likelihood of the offset of the
seabreeze local interaction with the gradient is getting
closer. Don't think it's just switching a knob and this extra
vector from the right is just gone…..
It's always an
unstable period (with more gusts and lulls than you've seen
all day or at the onset) and than a slow dropping of speed and
depending on where the gradient was suppose to turn to, a
gradual turning of the wind (between 18:00 and 22:00 hrs
depending on how strong the breeze system really got and all
the other factors).
So again you're going to race in shifty
conditions but with pressure dropping (so power up your
settings!!) and there might be a tendency towards the
forecasted north westerly direction.
But hold on!!
Seabreeze is starting in southwest and also slowly veering?
And than with the offset….??? Yes it might actually veer
further than the local effect of the breeze system because of
the gradient changing during the day!!! So what will happen??
To be honest
I'm not sure but at least with the expectation
of a dropping of the speed and a shifty period during the
races a lot of the big game plan can be made, and situations
anticipated.
I hope to have showed you in which way simple
principles can work for you in the praxis if you know how it
looks! So start looking up at crucial intervals! It helps you
to become aware of the system and translate the forecast of
the Met bureau into Real Time decision
making.
"We're going to have to be smarter than
the wind," somebody once said. I wouldn't say smarter ("cuz'
the wind ain't that smart") but more "aware of the principles
that it's driving it".
Good winds
Rigo de
Nijs
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