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Barometer aboard -- still a good idea

Jan 1, 2003
From Ocean Navigator #120 March/April 2002

From Ocean Navigator #120 March/April 2002

Barometer aboard — still a good idea

It has been said that weather is one thing mankind can do nothing about. While this is true, weather forecasting has become so sophisticated that even severe storms rarely take us by surprise.

Today, luxury liners cross the Atlantic in a few days, and the Concorde can cross the same ocean four times in a single day. Any large storm that might threaten our crossing by sea or air has its every move noted and transmitted by weather electronics to all interested parties. There was a time, however, when a trans-Atlantic crossing took months, and anyone embarking on such a journey knew they were departing into the unknown and that there was a good chance that they would never see land again. Life at sea was tough. Storms that could crush a hull like so many matchsticks arose unexpectedly. Thus, from the earliest of times, mariners have sought to devise better methods of predicting the weather.

Yet, for all the electronic sophistication at our fingertips, two facts remain as true as they were 300 years ago. Fact number one: Big storms can do bad things to little boats. Fact number two: Concerned boaters need to know all they can about weather so as to avoid fact number one.

Enter the barometer. Of all the navigational instruments found onboard a small boat, one of the most important is undoubtedly the barometer. Why so? Because the barometer is the instrument used to show changes in atmospheric pressure, and by observing these changes we can know what kind of weather system is heading our way. When the atmospheric pressure is fluctuating very little, it means the weather is apt to remain stable. A pronounced rise in pressure indicates fair weather will soon be upon you. Conversely, a slow but steady drop in pressure signals the coming of a storm — a time to turn into the wind and put the pedal to the metal.

But what is this “turn into the wind stuff?” Well, storms are at the center of extreme low-pressure systems, and since wind rushes toward the center of the storm to replace the air that is rising through convection into the upper atmosphere, it doesn’t take anything more than a pennant or weathervane to point yourself toward fairer weather — although there’s a bit more to the topic of storm avoidance than we can go into here.

With all the advanced electronic instruments on the market — some with meters for temperature, humidity, wind direction, wind speed, barometric pressure and more — why would anyone even want to consider using such a low-tech device? The answer is simple: It is a low-tech device. You hang it on the bulkhead, and it goes. There are no wires or batteries involved, and it can’t be affected by power surges or poor radio reception. Heck, you don’t even have to wind the thing. You simply buy a quality unit to start, calibrate it from time to time, and be prepared to pass it on to your children.

It is important to note that when it comes to barometers, beauty is no sign of quality. Many fine-looking barometers are cheap plastic instruments with a thin brass veneer, while some of the best are often lacking in aesthetic appeal.

As mentioned, all but the worst instruments will indicate the rise and fall of atmospheric pressure. However, good-looking, medium-quality instruments may be purchased for less than $100. High-quality units may be purchased for less than $350, and the very best — instruments that will compete head-to-head with lab standards — can be purchased for less than $700.

Using your new barometer:

1) Place the instrument where it will remain undisturbed.

2) Contact a local weather station, newspaper, TV or radio station for the exact local barometric pressure.

3) Turn the adjusting screw on the back of the barometer until the indicator hand points to a reading on the dial that corresponds to your known local barometric pressure.

4) Now, place the reference pointer over the pressure indicator hand to set the new reference mark. This will allow you to observe the direction and distance the pressure indicator hand has moved at your next reading.

5) Keep in mind that the rate of change is important, as the amount of change in forecasting corresponds to changes in the weather. Barometers are normally read once a day. However, during times of unstable weather, you might want to take several readings within just a few hours.

6) The hands on a barometer are very light and may be affected by friction. It is advisable, therefore, to tap the barometer lightly before taking the reading. In some cases the indicator may move several points. That is normal. Simply take your reading and adjust the reference indicator to the new position.

7) Finally, keep in mind that a barometer does nothing more than measure atmospheric pressure. With this information in mind, one can make some intelligent guesses about the weather that is soon to be at hand. It does not, however, forecast weather in and of itself. Thus, words adorning the face of most aneroid barometers, such as “rainy,” “stormy,” “fair,” “dry” and the like, may be taken at face value, with that value simply being an adornment on the barometer’s face.

William Cook

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