My father is on the way to Oman for the Master Laser Champs and he had some questions about the weather graphs posted on the
worlds website, and since he has been reading RYA Tactics but he doesn't use a compass he had some questions about how to pick up on things without a compass. Since this is off-season for many of us, it is also the season for reading up on tactics theory so I figures that I would share my response with the blog followers. So here are some of my thoughts based on the first four days of weather graphs at Oman, which are available here:
Day 1,
Day 2,
Day 3,
Day 4 (of the Laser World Championships which run directly before the Masters Laser World Championships for which my father is preparing).
At the bottom left of the weather graphs (
click here to go to the page that leads to the weather graphs) there are a few viewing options. Under "Radar
Graphs" on the left there is a circular graph where the distance away
from the centre is the percentage of the time that the wind spent at
that angle, and the side of the circle indicates the direction that the
wind was blowing from. So from that we can tell that the wind rarely
shifts more than 10 degrees each way when it is coming from the East South East.
On days 2 and 3 the graph is very slightly skewed left, which would
indicate that all else being equal (and is probably not) it is more
likely that if you went left you would get a left shift to help you get
back to the middle of the course than if you went right. So
the
strategy on a big course would be at the bottom of the course to head
left while the course is square and then to tack back in any time you
get knocked with a leftie, then once you are most of the way up the
course start working back right any time the wind comes back to neutral
or left, only tacking back towards the left when there are relatively
bigger (10 degree) righties because they shouldn't last long (the reason
that you would work back right would be so as not to get in trouble
with the busy layline). That is digging pretty deep for strategy, I
think that for a lake sailor the breeze would seem very stable.
Day 2 and 3 and also Day 1 have the wind exactly at the
median about 45% of the time,
whereas on Day 4 there is a range of about
10 degrees that the wind stays at for just under 25% of the time, which
is the median. Also the wind fairly regularly shifts ten or more
additional degrees either way outside of that range. So that is a
situation where it would look more like lake sailing. Lots of shifts
and not so much of an obvious median. So with the information we have
looked at in this graph it seems that the strategy in a Northerly (NNW)
would be to be very sensitive to wind shifts and to stay on the lifted
tack as the most important part of your strategy, more important than
getting to a specific side or other tactical considerations. Looking
closely at the graph it looks like having wind from the NNW is slightly
more likely than 350 degrees, but I think that the wind is spending more
time to the right of 350degrees than to the left of NNW, so if in
doubt, I would work my way right (after looking at other graphs that take into account time this
proves to be correct for more reasons). The thing is that at the regatta you won't get the info from
these graphs until after the races, so it will be interesting to see
whether we get a few more Northerlies to see whether the slight
right-skew holds. If that is a pattern then you could make a plan based
on it, but it is possible that Northerlies are just very random. So we
should keep checking in on these graphs to see if we can pick up on any
recurring trends. Do you know whether Northerly is an off-shore
breeze in Oman?
To be honest I don't know that the bar graph to the right
on the Radar Graphs page is measuring, I think it has to do with wind
strength. But I think we can learn more about wind strength from the
Wind Polar Graph tab.
Wind Polar Graph: On this tab you see pink dots
measuring the wind direction and strength. The further away from the
centre the windier, and you can read the actual wind speeds by following
the curved lines over to an axis (and ignoring the negative signs), so
if you click backwards and forwards between Days 2 and 3 on two browser
tabs, they look like they are different, but if you read the mean wind
speed (yellow dot), in both cases it comes to about 13 knots, they have
just scaled the axies differently between the two tabs. So Days 2 and 3
so far
look like carbon copies of one another in wind speed as well as
direction. Day 1 which was a few degrees right of Days 2 and 3 when we
looked at it under Radar Graphs has its mean dot also at around 13 knots
but there is a bigger spread between lightest and heaviest wind (and if
you click back and forth between Days 2 or 3 and Day 1 under Wind Polar
Graphs you can see
that the dots are indeed a bit further right on the
circle). This could mean that when the wind was a bit further right
(Day 1) it was puffier and there were bigger holes/calm spots (after
looking at other graphs it turns out that it was actually because of a
building trend in the wind). In contrast Days 2 and 3 had blobs of pink
dots that were more circular indicating a more random distribution
around the mean, less variance in wind strength. With these pretty
well symmetrical graphs (Day 1, 2 and 3) you don't have to think too
much about relating strength to direction, but on Day 4 the graph is not
symmetrical about the centre point of the circular graph. The further right the wind went, the stronger the wind
was. That is hugely important, that means that the puffs came more from
the right in this case in a northerly (let's see if that happens again
another day), so after looking at the Wind Radar graph we thought that
it would be slightly beneficial to go right just because the wind spent
slightly more time coming from the right. We can now gather that during
these periods when the wind went right it was also stronger, so now the
strategy becomes to sail out right whenever there is a lull until you
hit a puff which is probably also a right shift (header) at which point
you tack on the header and sail back into the middle of the course
cashing in your gain from sailing fast in pressure. The trick here is
to recognize as you come back into towards the middle when you are no
longer in pressure. Puffs are usually pretty dramatic, but lulls often
sneak up on you gradually, so you have to be careful to recognize when
you are going slower and in this case when you start to get knocked.
When you recognize either of these you would tack back right for more
pressure. Because this is relatively difficult to realize, I'll offer a
couple more cues to pick up on. One would be that the puff might be
visible on the water (in this case you would be expecting it on the
right). Look for darker water on the right in the distance. Depending
on how distracted you are and how much salt water has caked up on your
glasses you might not be able to see the shifts early enough. If you
see the puff too late it is often not worth going for them because you
end up getting there after it is no longer a significant puff, or the
direction has gone back to mean. Or you even end up over where the puff
was when it is now a lull. That is what we are talking about when we
say that someone is "chasing puffs" or someone is "out of phase [with
the wind]" in which case they might start taking on lifts instead of
headers or tacking on headers that only take them back to the median
wind direction. Another more obvious cue to tack back over to the
favored side is if you see a group of boats sailing towards you. In
this case you have the option to tack and sail in the same direction as
them or you can duck or cross them. In this Oman Northerly situation
you would want to resist the temptation to use up your slight starboard
right of way advantage to cross someone and instead tack with them
before you get too close to them so as to to lead them on port towards
the next right side shift/puff. If you tack to lead a group of boats
towards the favored side with enough distance between you and them you
will not be pinned when you finally get to the puff and get knocked and
you will have enough leverage (lateral distance along the race course)
to gain some noticeable ground on that group. Tacking to lead a group
requires you to be shuttling your focus fairly well so that you are
aware of the group of boats coming before they are on top of you.
Another consideration in these conditions is not to overshoot the right
layline because you get so carried away with leading rightward. That
being said, if there is good pressure out on the right spending a bit
more time on or slightly over the layline in pressure is not the end of
the world if the alternative is to be sailing in lighter dirtier air
further left on the course.
The main thing that we have not taken into account so far
in looking at the graphs is whether any of the trends that are
happening are related to time. Time is important because with the current information it conceivable that on Day 1, with the data points that spread more between light and heavy
wind, the wind could either have started out heavy and became lighter or, more
likely in a sea breeze environment, the wind could have started out light and
became heavier (with the next graph we find that the latter is correct). If one of
these is the case then our worries about there being big puffs and big
holes are not well-founded, for example it could have been a very
gradual increase in wind without obvious puffs or lulls. So lets check
out a graph that factors in time of day: Click on the Wind Graph tab.
Wind Graph: There is a lot going on in these graphs. As
indicated to the right of the graph the red line is the wind direction
and the blue is the wind strength. The scale for the wind direction is
recorded on the left of the graph and the scale for the wind strength is
recorded on the right of the graph. The peaks and troughs of this line
indicate how drastic the shifts typically are, so on Day 1 we are
seeing mostly 5-10 degree shifts until 18:05 =6:05pm, then things start
getting
a bit more crazy with bigger 15 degree shifts for the next half
hour. Interestingly at 18:05 you also see the wind strength start to
dip. So this is a familiar situation: the wind dies a bit and starts to
shift more dramatically "goes light and shifty" for a half hour. But
before you get too carried away with imagining that, you have to read
the scale: according to the scale this brief dying trend is only from
about 13 knots to about 10 knots, so nothing too crazy. Later on the
wind picks back up again and becomes relatively more stable. One thing
that will be difficult for a lake sailors is figuring out these longer
period shifts. It appears from the graph that many of these shifts are
taking as much as 5 minutes to turn one way before coming back the other
way. On our lakes we are used to shifts lasting maybe 30 seconds or
less, up to a minute or so and we are used to tacking on them
immediately so as to cash in on a relatively short course. It is hard
to know how many times per minute the measurements for this graph were
taken, it could very well be that the measurements were taken over such
long periods that the 30 second or less shifts were not picked up.
However I imagine that Oman is a big open sea venue and in these venues
the shifts often do take a lot longer to pass through their cycles. So
as a lake sailor you have to have a lot more patience. Wait two or
three times as long as you are used to. When you feel a shift you can
think about it: is this a particularly big shift or not? Was it just an
apparent wind trick as a result of turning up and down through the
waves or from a puff or lull? If I tack on this will I be going the
right way in the grand scheme? Then you can tack on the shift after 5
seconds of deliberation (assuming there is no pressure form other boats
to make the call more quickly). This is in contrast to lake sailing
when a half second means a half boatlength because the course is short
and the shifts are quick.
Anyway getting back to the overall analysis, it looks
like Days 2 and 3 are not quite as identical as it seemed from the other
graphs because whereas Day 2 has the wind slowly and steadily building
through the 3 hours of data, Day 4 has a consistent amount of wind
throughout. In a building breeze it is even more important to get clear
air especially on the downwind so that each new wave of increased
pressure is actually carrying you forward, rather than just getting
lost
in the crowd of boats around you. However that also goes for other
wind trends. Day 1 also seems to have a building trend, but that lull
around 18:20 is interesting. It could be that there were roving lulls
(holes) around the race course and it just happened that a lull passed
by wherever the weather instruments were over that period. Day 4 on the
other hand appears to have some crazy stuff happening. The wind
strength was pretty constant with maybe a 2 knot
increase over 3 hours.
But directionally there was some interesting stuff. Before getting
into the really wierd lines on the graph towards the end of the day,
let's look at some of the stuff earlier on. From 11:45 to 12:15, so
easily enough time for a leg or two, the wind did a persistent right
shift, meaning that you would have had to sail a header into the right
of the course in order to sail a lift back into the mark, thereby
sailing the inside track of the persistent shift (sailing a shorter
radius along the persistently curved track). That would have been a
very difficult strategy to decide on however because for an hour before
that period the wind seems to be oscillating pretty randomly. Also it
turns out that if you had been unlucky at the end of that trend you
would have been caught by a 35 degree leftie over 5 minutes leaving you
totally screwed on the right of the course unless you had already made
it around the mark (at a major event like this they would most likely
cancel the race with a shift like that). The fact that that giant
leftie could come in and ruine a well thought-out tactic seems pretty
disheartening, but it could be seen as encouraging. I know that I often
make tactical decisions that I think are sound and then end up getting
screwed. In the absence of this graph I could think that my (perfectly
sound) tactics are flawed, but here we have, recorded on paper proof
that there are situations where essentially correct tactical decisions
could get you screwed. This is why we have drop races. But before
abandoning hope in the race if something like this came though, there
may have been some telltale cues to pick up on in the scenario where
this is a race that doesn't get cancelled, cues that would not have
saved you, but could have minimized the damages. If you keep shuttling
focus between your boat speed, your boat on boat tactics and the overall
fleet position, you might have started to notice some boats on the
opposite side of the course pointing in a very strange position, or
maybe a wind line appeared on the horizon or on the sore line at the
left. Maybe a flag or a smoke stack upwind started showing warning
signs of a bizzare direction, or maybe it is very last minute and you
just notice the boats upwind of you getting the shift. At that point it
would be too late to cross the course and get to the left before the
shift hits and if you tried to cross over you would have ended up lost
in the middle of the course. This is where the principle of 'winning
your side' comes in. The group of sailors way out left who are now
winning by a lot because of all the distance they have away from you
(leverage) are not worth taking into account, but if you can get to the
left of the boats on your (right) side of the course as this leftie
fills in you will at least be ahead of the boats near you and so you
have minimized the damages. You will be behind the people who went left
but ahead of the people who wend right and that's how good sailors get
consistent results. They don't buy the lottery ticket and go left when
the fleet's tacticians go right, they go to the apparently favored side
and benefit from it most of the time and minimize the damages the odd
time that it doesn't pay.
At about 13:15 of Day 4 it looks like there was an insane
direction switch with across the graph but this is not the case, this
is just bad graphing. The compass is a circle, so, for example a 10
degree shift could take you 355 degrees on the compass to 5 degrees.
This is a 10 degree shift, not a 350 degree shift as the graph would
have you believe. So the thin black trend line is incorrect, this is
not a hard right shift, but a slight left shift. So after our half hour
right trend that I just discussed ending at 12:15, there was actually
an hour and a half trend left over 35 degrees from about 335 degrees to
about 10 degrees (remember that 0 degrees aka 360 degrees on a compass
is North). If we look back at the Wind Polar Graph from Day 4 we can
see that
what most likely happened was that at the beginning of racing
the wind started to the left and was lighter (than the yellow dot) and
throughout the day the wind got slightly windier and went much further
right. In general it is not worth looking at the black and red dots
because they only represent a couple of data points and because of
random variation they could give you all sorts of misleading
information. But in this case they happen to be consistent with our
theory. The black dot representing the last minute of data was indeed
further right and windier than the yellow dot that represents an average
from the whole day. The last 10 seconds (red dot) happens to line up
with the directional trend by being even further right than the black
dot, but ten seconds is such a fleeting moment that I don't read much
into that or the fact that it is slightly less windy than the black dot.
So ya there is a lot that you could read into the graphs, the perils of asking an engineer about a graph...
Your
other question was about how to pick up on shift directions without a
compass. It is possible that in Oman on one tack you might be pointing
towards a shore. In that case you can take a transit each time you tack
and as you sail on a shoreward tack, keep an idea of where your boat is
pointing relative to any landmarks or buoys on the water. The problem
with this relative to a compass is that each time you tack you have a
new transit that you can't really compare to the last one because you
have sailed up or down the shoreline. With a compass you can compare
headings on one tack and with a bit of mental math (adding or
subtracting your tacking angle) you can compare your heading between
tacks. In the absence of a compass when you are using transits try to
imagine a transit that leads from your centerboard through your mast and
through your bow eye straight forward. Unless there is current, this
should stay constant until you get a shift. In contrast, if you are
hiking hard and you sight through your mast because just because it is
convenient your transit will change as you sail forwards and shifts
could be harder to pick up.
Unfortunately I expect that there will rarely be any
usable transits in Oman, so you have to pick up on other cues. Try to
keep an impression of how the other boats look relative to you and have
an idea of who you can see through the window in your sail and who you
cannot. Then you can reverse this trick and get an idea of whether the
other person can see you through their window or not. I think that
depending on where I am sitting, I can usually cross someone who I can
see through my window, especially if they are far away, and conversely
someone will probably cross me if they can see me through their window.
If you check in regularly with this and other visual cues (am I looking
more straight at that boat's transom or bow or more at the side of
their boat for example) you can get an idea of who is lifted, who is
knocked and who you will or will not be able to cross. That is not to
say that crossing them is important, it is more about figuring out which
ladder rung of the race course you are on. if you can cross someone
you are on a higher ladder rung than them. Instead of crossing a person
it is usually much more important to follow your game plan and that
usually means tack with a boat or set of boats to lead them to the
favoured side of the course regardless of whether you are on a higher or
lower rung than them.
On the other hand if it is an even race course and the game is to
tack on the shifts, you can pick up the shifts like this. When it is
shifty you will notice that one minute you can cross someone and the
other minute they can cross you. Let's start out with another boat on
the same ladder rung coming towards you on the opposite tack. If you
suddenly realize that they are now able to cross you when they couldn't
have before, tack, because you have been knocked and they have been
lifted. This also lets you get to the next shift first and lets you
cash in on the leverage between you at your next advantage. If, in the
other situation, you realize that you are now crossing someone who you
wern't before, keep sailing towards them because you are lifted and they
are headed and you want to close the gap between you and reduce the
leverage so that even if the other person gets another shift later on,
the distance between you will be less so they will gain less relative to
you what you gained when there was more separation.
Other cues to look for on the race course can be marks of the
course: reach marks, the windward mark (leeward mark on the downwind),
navigation buoys etc. These cues and the boat-on-boat cues are
important to pick up on regardless of whether you have a compass. For
example if you did have a compass you might have your compass telling
you that you are sailing in consistent breeze, but your windward mark
telling you that you are knocked. So after you puzzle that one out...
you might realize that in fact you are not getting knocked, you are
being set down by the tide/current, so later in the upwind leg, you will
actually have to overshoot the layline to get around it. One
limitation of the compass is that it tells you your own wind condition,
whereas this type of visualizing of the whole fleet can give you
information about other parts of the course or about parts of the course
yet to come for which you can get prepared early.
Before the start the best way to keep and eye on how the
wind is tracking without a compass is to keep an eye on the committee
boat and the pin and go head to wind regularly. Ideally there would be a
transit to take when you go head to wind but that probably won't be the
case. Instead visualize the imaginary line from the committee to the
pin and see how square your boat points to this imaginary line when you
go perfectly head to wind. I find that this is easiest to visualize
this when I am very close to the committee boat or pin (pin is usually
less crowded) and when I stick my hands out either side of my boat in a
line perpendicular to the breeze, a line that would be parallel to the
start line if the start line was square to the current wind direction.
Obviously this process falls apart without a compass if they move the
committee or pin, but if they do that it is usually a recognition by the
race committee that the shifting trend is going to stay, or even a
prediction by the RC that the wind will shift probably based on radio
info from their mark boat way upwind, so it is very valuable
information, maybe the trend will continue... So keeping an eye all the
time on the actions of the race committee and comparing the angle of
your outstretched arms to the angle of the startline can be a nice
substitute for (or addition to) a compass and it can help you get a feel
for the frequency of the shifts, do they come more or less every
minute? 5 minutes? When you are doing this it is also important to
take into consideration that the RC may be skewing the line because of
tactics on the race course: if you must get left to get out of adverse
current , a good RC would purposefully set the committee upwind of the
pin, or committees will often favour the pin when all else is even
because lots of people prefer to start at the committee out of habit and
because committee-end starters have the option to tack out more
easily. So you could be pondering whether any of these things might be
coming in to play when you compare your own measurements to the angle of
the start line.
