SEA BREEZE
It did not take me long to realize that the more you know about the weather, the more it helps your sailing skills. I grew up sailing on Narragansett Bay and now spend most of my time sailing/racing in the Marblehead area. Marblehead is a great place to sail because not only is it a beautiful area, there is a predictable sea breeze that fills in around noontime everyday in the summer. This sea breeze makes for very exciting sailing.
So if we are going to race in this sea breeze we need to know what is a sea breeze and what causes a sea breeze. The sea breeze develops when the summer sun heats up. The land heats up much more and faster than the cool ocean. As the land heats up the air rises, remember hot air rises, causing and area of lower pressure over the land. The cooler air over the ocean rushes to the land to fill in the area of lower pressure. We also know that areas of higher pressure will always flow toward area of lower pressure. Blow up a balloon and the additional pressure of you filling the balloon makes it expand. Open up the balloon and the higher pressure in the balloon runs out to the surrounding air to equalize the pressure.
The movement of the air from areas of higher pressure to areas of lower pressure is called wind. The greater the difference in pressure the higher the wind speed. Like a hurricane has really low pressure causing a big difference in the atmosphere around it and causing very high wind speed. These differences in pressure are shown on a weather map by isobars. The closer the isobars the great the difference in air pressure the higher the wind speed.
In the summer the weather moves very slowly so the effects on the weather become very local. In the winter the weather moves much quicker, therefore low pressure cells traveling west to east cause much of our day-to-day weather. We see very little sea breeze effect in the winter.
If there was no other effect to the weather the breeze in Marblehead would be out of the west. That is called the prevailing breeze and is also why most of our weather comes from the west. Black clouds to the west of you mean that soon you will get hit by thunderstorm, but to the east no worries it is past you.
So we wake up to a beautiful Marblehead summer morning and the breeze is out of the north/west. The land has cooled off over night and the reverse of the sea breeze is happening. The air over the ocean is actually warmer than the land, so it rises and the cooler air over the land moves to the ocean an area of lower pressure. So we head out for our day of racing with a light northwester. The breeze feels good and certainly is enough to race in. We notice there is more breeze close to the shore since that is where the cooler air is reaching the warmer air. We are noticing that as we get closer to noon, the breeze is getting weaker and finally it dies all together. Note there is always wind, therefore if you feel no wind it is because 2 opposite breezes are canceling each other out.
It is noontime now and looking over the land we see big puffy clouds developing. The clouds are the water vapor rising over the land that is heating up. If the land is now heating up very soon the cooler air over the water will move inland causing the sea breeze. Sure enough whispers of wind begin to fill in from the ocean. The true wind direction of the sea breeze is a little south of east say 120 degrees, however the prevailing breeze, southwest, pulls it south so your first wind direction of the sea breeze will be about 165.
This little battle between the prevailing breeze and the sea breeze will go on all day and will cause the shifts that will make the winners win and the losers go home talking to themselves.
The race committee postpones at 11 due to the no wind, but now at 12:30 we have 8 knots from 165 and the race sequence begins. The course is windward leeward twice around 2 mile legs, race committee posts 160 as the heading to the windward mark.
Start at the left or pin end and go until you are 10 degrees short of the lay line. Tack to port and you will get lifted to the mark. As the sea breeze builds it will prevail more and more over the prevailing breeze moving more left all the time, probably going as far left as 145. There will be small movement back and forth with the direction, but the trend will be to the east.
The breeze should build to 12ish and will build from the east again favoring the left side of the course. Downwind protect the east side of the course, again if the breeze builds it will trend to the east, if it begins to die it will trend back to the south.
The second up wind leg protect the left, but more import stay between your competition and the mark. You will probably begin to see some bigger shifts to the right as the prevailing breeze as more effect. The last down wind leg stay between your competition and the finish.
There are a million variables to this basic scenario, which is what makes yacht racing so interesting or frustrating depending upon how you look at it.
In the summer the sea breeze cools us down and makes for great sailing.
Please mail comments to me at Bump@newwaveyachts.com
Bump Wilcox
