Emergency Navigation

[HenryC]

Florida Wildlife, Jan-Feb, '09

Most boaters get around by piloting, the ancient art of finding your way by using landmarks. This can be as simple as simply looking around, the way you navigate around your house; or you can use chart and compass and simple drafting tools to plot your position and course with some precision.  With a timepiece and some means of roughly determining your speed  you can add dead reckoning to your navigation by making estimates when landmarks are scarce or hidden by weather or darkness.  These simple skills served us well for centuries before GPS and other electronic aids  helped us find our way.

But electronics are delicate and dependent on electricity.  And worse than breaking down, they can give false readings which can get you into terrible trouble.  Even when working perfectly, if you lose confidence in them they're worse than useless.  Sailors as well as pilots  have to learn to trust their instruments, but that is no excuse to not look out the window. Even the normally dependable magnetic compass can fail, or get out of adjustment, or the gadget-addicted skipper may simply forget how to use it. The fundamental navigational question is not "What is my position?"   It is "What course do I steer?"  Human beings lack a natural sense of direction. Without electronics, or a compass, or visible landmarks, even the most competent seaman is hopelessly lost.

It is essential that the boater maintain situational awareness, that he instinctively knows where he is and which way he needs to go. Not only does this provide a constant check on his navigational methods and equipment, it also gives the confidence and self-assuredness that (along with caution) distinguishes the seaman from the weekend boater.  When totally blind (in a thick fog or out of sight of land) and when no other method or source of navigational data or estimate is available, the prudent thing to do is stop; drop the anchor if you can and conserve fuel.  Otherwise you will simply wander around helplessly in circles until you are out of gas and far from home, or both. It is no disgrace to admit you are lost and to wait until the fog lifts, or the sun comes up, or the stars come out, and they always will.

People were traveling long distances in boats for thousands of years before the compass was invented: sailors need to know the sky.  It isn't necessary to be an astronomer or celestial navigator or even to know the stars and constellations by name, but you should have a general idea of the layout of the heavens so that day or night, if it is clear, you can get a rough idea of direction.  And you will learn that the better you get at it, the more fun boating will be, and the safer and more confident you'll become.

Seen from a point high above the north pole, the earth rotates counter-clockwise--from west to east.  From any point on earth, sun and stars appear to rise in the east and set in the west. But this is somewhat misleading.  The celestial bodies do rise in a rough easterly direction, travel all the way around the sky and set more or less in the west, but not precisely.  It all depends what we're observing, the time of year and where you are on earth.  It's like we are inside a giant black globe and the stars are painted on its inside surface.  In fact, this is what our ancestors actually believed, they called it the celestial sphere, or the "firmament".  We know today it's the earth that spins around once a day, but it's still helpful to think in terms of an imaginary  sphere rotating around us every twenty four hours, half dark, half illuminated by the sun..  The appearance of this sphere and its angle of spin to the horizon depends on where on earth we happen to be.  And the motion of those lights pasted on the inside of the sphere will depend on where on the sky they are located. 

Because Florida is fairly close to the equator, eyeball navigation by the stars is easy.  But the sun rises due east and sets due west only on the first day of spring and fall, the equinoxes, around the 21st of March and September.  It rises more and more to the north as spring turns slowly into summer, stops it northern journey and heads back south around summer solstice on  the 21st of June until it rises as far south as possible on the winter solstice, the 21st of December, when the cycle of seasons repeats itself.  Because Florida is near the tropics, the sun never rises or sets more than about 27 degrees from due east or west.  (All measurements in this article are rounded off.)  So if we make a rough correction for the season, we can make a pretty good guesstimate of where the compass directions lie.  Using azimuth angle to indicate compass direction; the azimuth increases clockwise from 0 at north through 360 degrees.  In fact, we define the direction where the equinox sun rises above the horizon as the "east" (azimuth = 90 degrees). If we face east, "north" (azimuth 0) will be to our left,  "south" (azimuth 180) will be to our right, and "west" (azimuth 270) will be behind us.

Example: if you go boating on May 1st, the sun will rise half way  between azimuth 90 degrees and its northernmost rising azimuth of 63 degrees. This is because you are halfway in time between the spring equinox and summer solstice. That day the sun will rise 13 degrees north of due east, and set 13 degrees north of due west, i.e., it rises at an azimuth of  77 degrees and sets at an azimuth of 283 degrees. This will vary slightly, depending on how far north or south in the state you are. Sunrise azimuth will vary between 90 at the equinoxes plus or minus 27 degrees at the solstices, so the solar azimuth will always be between 63  and 117 degrees at sunrise and between 297 and 243 degrees at sunset

In Florida, the sun at noon will always be in the southern part of the sky, and that can also help you get oriented.  At solar noon, the sun is due south of you and at its highest point, but you have to be careful in the subtropics.  At its highest point (June 21), the sun is almost directly overhead at noon in Key West, and practically useless for determining directions. In the northern part of the state, you are only a few degrees of latitude further north, so it doesn't help much either, especially from the rolling deck of a boat.  At its lowest point, solar noon on December 21,  it will be about halfway between the southern horizon and the zenith, so it can be very useful for getting yourself oriented.  It will be due south of you.

Except for a month or so around the direct overhead sun of summer solstice, you can still make good noontime direction estimates if you know the local standard times of sunrise and sunset and noon, and make allowances for them, but don't forget these times will vary due to Daylight Savings Time, your longitude, and other factors.  In other words, the sun is not at its highest point in the sky when your watch reads twelve.  Keep a copy of the day's newspaper with you on your boat (it comes in handy because it lists the tides, too); solar noon will be exactly halfway between the times of sunrise and sunset. At solar noon, the sun will be due south of you.

At night, you have no sun as a compass, and the stars are scattered all over the celestial sphere. The Belt of Orion (if you are familiar with your constellations) is on the celestial equator and therefore always rises due east, and sets due west, just like the equinox sun, no corrections necessary.  At its highest point in the sky, it is due south of us at an elevation of  60 to 65 degrees from the southern horizon, again, depending on how north or south you are along the Florida coast. Unfortunately, Orion's Belt  is not visible throughout the year, it may be lost in the sun's glare or  it may be below the horizon when you need it.

In general,  you are going to have to use a different nighttime guide: the North Star,  Polaris.  Polaris is not directly over the North Pole, but it's close enough for eyeball navigation.  So as the celestial sphere rotates on its axis, Polaris does not rise and set, it is always in the same spot, unmoving, like a little tiny "N" drawn in the sky for the convenience of the navigator..  If you look at Polaris, you are looking due north, and the whole sky is rotating counter-clockwise around it once every 24 hours. In the northern hemisphere, except for those stars and constellations close to the pole that appear to circle it all night, celestial objects generally rise in the eastern half of the sky, reach their highest point in the south, and set in the western half. 

So how do you find Polaris with all those thousands of stars up there?   Polaris will be second magnitude (easy to see but not really bright) at an elevation above the northern horizon equal to your latitude.  In the Keys, it will be 25 degrees above it; in the Panhandle, 30;  in either case, about one third of the way from the horizon to the zenith.  It is easy to find, there are no other bright stars near it.  Go looking for Polaris every time you go out on a clear night when you know which way north is, memorize the stars and constellations near it like the Big and Little Dippers (but keep in mind they are always in motion so they will always look different  throughout the year and the night).  A book on astronomy, or a friend who is familiar with the sky can help. Familiarize yourself thoroughly with the northern sky so that if you ever need to find north you will recognize it instantly. Someday your life may depend on it. But even if it never comes to that, as you learn more it will all start to make sense and it will become easier, you will want to learn more. 

With just this basic knowledge of astronomy, you can never be totally helpless as long as you can see the sky.  Even if you don't know where you are, you'll know which way to go, you will be oriented. You will not just be out on the water, you will be totally aware of your surroundings, an integral part of them, from the coasts and islands near you to the earth and your place on it, all the way out to the distant stars that now guide you. You will be at the center of the universe, and you will know exactly how you relate to it. Take my word for it, there is no other feeling quite like it.