How to Win

Mastering the weather

Well, you know what they say, you cannot control the weather… but you can take advantage of it, even if it is just to ensure that you are more psychologically prepared than your rivals. Jon Emmett explains all

Basic understanding of weather is so important whether you are a weekend warrior or an Olympic campaigner. So fi rst we need to understand some basic terminology:

Stability is about thermal mixing, whether the wind is going up and down. Th is is not the same as a shift y wind. Th e wind can be very stable (no vertical mixing) and change direction a lot or can be very unstable (lots of vertical mixing) and come from the same direction all day. More on this later.

Pressure is about an area on the water where there is more or less wind, for example behind a large building there may always be less wind because the wind rises to go over the building or goes around it (Fig 1). Th e is why you never want to set a racecourse / windward mark close and directly behind a very tall land mass because the wind will seem to come from every direction with huge diff erences in pressure across the course. Th e thing which is easy to forget is there is also less wind just in front of the building / land mass where the wind rises to go over it.

Th ere may always be more pressure between two hills (Fig 2) because it takes less energy to go around the hills than over. Pressure does not move: it is an area of wind (more wind or less wind) dictated by topography. Gusts on the other hand move down the course, so you can position yourself so that they are “coming to you”.

If wind were a person, then they would be lazy. Like water, wind chooses the path of least resistance which like rivers is the reason that wind bends. So, before we look at the general rules that we are taught in many textbooks we need to consider what sort of day it is.

Fig 1

Fig 2

On a cold day.

e wind tends to be more stable. ere is little heating and o en there is thick low-level cloud which blocks the sun and means the wind doesn’t travel up and down much. ink UK South coast in a north easterly breeze as a good example but of course the wind could come from any direction:

O shore breeze There are faster and more gusts and shifts by the land.

Take the shifts and the pressure but be careful to be in the pressure before tacking / gybing because the pressure won’t move.

Gusts will be fast moving so reward “snappy sailing” (be quick to react). Land on the left Cold land means more friction over the land. So, the wind near the land is generally left but also lighter and more unstable because even on a cold day the land will be warmer than the sea. Slightly o shore there will be more pressure. Land on the right Again, more friction on the land, and wind doesn’t like friction so less wind close to the land. Wind will also be more stable as you go slightly o shore. O shore breeze With the warmer wind expect bigger areas of pressure and maybe less wind if you go too far o shore.

Top tip; the windier it is the stronger friction and mechanical turbulence means the gusts/shifts move more, so you don’t have to sail so far into gusts before tacking or gybing. Land on the left Now we have vertical mixing and the classic conditions that most textbooks talk about is correct. The warm land brings the stronger winds down to the surface because of the vertical mixing so more pressure on the left near the land. Land on the right We are now on the edge of having a sea breeze and depending upon the temperature, this would turn the wind to the left. Expect less wind close to the land, again like the textbooks.

If you have large black clouds, they will be dropping wind and rain. e closer you are to the clouds the sooner you reach these gusts.

On a warm day:

e sun is shining and now the wind is more unstable due to heating. Like water when hot, wind behaves di erently. A test you can do for yourself is close your eyes and listen to someone pouring boiling water into a glass and pouring ice cold water into a glass. You can even hear the di erence! It is the same with wind, cold wind you can consider heavy and less likely to rise. Remember a day could be cold in the morning and a warm day in the a ernoon, these are the days to get your head out of the boat around midday.

If the gradient wind is onshore, then it is a very open sector, but we need to remember that the wind does li up and over high land. So, like a reverse wind shadow e ect there is less wind just under tall buildings / land masses as we looked at earlier. So, all things being equal head o shore (this article only deals with wind, not current!)

Large white clouds are formed over the water where the wind is going vertically up, so there will be less wind under these large white clouds…. Keep away from them!

On a sea breeze day:

When talking about this we have some key ideas. Cloud cover forms a blanket over the land, so a cloudy night will keep the land warm, whereas a blue and cloudless sky you will feel the night-time temperature drop very quickly! O en in the morning you will have a cool, calm day before the day heats up. ere may be a good gradient breeze in the upper levels but initially with no mixing, no wind at sea level. On such days you see no wind on the water initially but the clouds above are moving fast.

Remember temperature of the land is more important than friction, and at rst we have cool air higher up that comes down when the warm air rises. e more heat a land type can absorb the bigger the temperature di erence between land and sea and therefore better the sea breeze (think sand is good at heating up, whereas forested areas don’t heat up because the trees absorb the sunshine energy). A good indicator of sea breeze is tall, clearly de ned clouds forming over the land and clear blue sky over the sea.

In essence we end up with pu y conditions with warm land which is a factor of the wind’s vertical stability. is means gusts rather than pressure. e stronger the wind the more any mechanical friction is noticed, wind going around land masses and buildings (in light winds the wind may not be able to pass around). e reason we have weather in the rst place is because the earth is hot around the middle and cold at the top and bottom and we get pressure systems forming where the hot and cold meet. Heating is o en the most important factor in weather.

Sea breeze is o en very over simpli ed, and it will nearly always have an e ect (whether to increase or decrease the wind you are sailing in or subtly alter its direction) although this can be masked. erefore, it is important to understand the “true sea breeze” direction for any venue. is will be relative to the main land mass, for example a coastline with runs east and west, rather than the angle of the speci c bay you are sailing in, which could face east or west. Maybe time to get out google maps...

The UK South Coastline is approximately running East to West and favours a true sea breeze direction of south westerly.

However, Torbay for example faces east…. Straight O shore breeze

Left diagonal o shore breeze (north westerly on the South coast of the UK)

Right diagonal o shore breeze (north easterly on the South coast of the UK) Wind gradually turns o shore. If the gradient is weak you may still have o shore wind close to land and sea breeze further out. This is best gradient wind direction for a good afternoon sea breeze. Wind gradually turns to the left as it is established (south west on the South Coast of the UK). Then mid-afternoon you have a persistent right shift for the rest of the day (back towards the gradient wind direction). So mid-right of the racecourse usually pays. Here the sea breeze is opposing the gradient wind. So initially the wind is calm close to land until it fi lls in and then slowly veers.

An exception to this is if the gradient is strong then you can get a south easterly, rather than a “true sea breeze”. The stronger the sea breeze the more likely it will dominate and will try and turn to the right, whereas the gradient is pulling the wind back to the left… think how much heating we have had and how strong is the gradient?

Onshore gradient winds ght the formation of sea breeze so you can sometimes end up with a gradient wind in the morning and evening and no wind during the a ernoon. Unless there is enough heating to overcome the gradient and produce a sea breeze. Alternatively with a very strong gradient and little heating means the gradient wind remains and the sea breeze just decreases the wind mid-a ernoon.

Race day – what do we need to do to win races?

We all have our favourite style of sailing and the best sailors in our sport can excel regardless of the conditions, they have all the tools in the toolbox! On extremely strong winds days it is about boat speed, boat handling and keeping it simple (any shi s and gusts will become very obvious) but most of the time it is about choosing your race strategy depending on what time of day it is.

Good weather forecasting is of course vital, and the weather models are now so much better than they were 30 years ago, but nothing beats the “nowcast” so think about what to expect and then get your head out of the boat on the racecourse and think about what is really happening!

Light winds Very small di erences in wind speed make a big di erence to hull speed. So, pressure is king. Be bold and play the favoured side. Sometimes the gusts will come both sides and the middle misses out! Medium winds Assuming stable wind then this is just basic sailing. Find a good lane, sail fast and in phase with the shifts. Being positioned roughly in the middle of the fl eet is safest. Unstable winds Ignore what is going on for the fl eet. Focus on the gust/pressure/shift around you. Get your head out of the boat.