Captain Jack's Celestial Navigation - Softcover

Davis, Jack I.

Softcover

ISBN 10: 1892216183 ISBN 13: 9781892216182

Publisher: Bristol Fashion Publications,US, 1999

Synopsis

Captain Jack I. Davis has done it again! He has written yet another, very easy to understand, instructional navigation book. As in his first book, Captain Jack's Basic Navigation, this book is filled with knowledge, new sea stories, and more humorous anecdotes. Using the same highly successful format of his first book, Captain Jack takes the reader through each phase of navigation by first explaining, in detail, the steps needed to complete each phase. This is followed by a list of questions to answer, using your new-found knowledge. After you have completed the questions, you can check your answers at the end of each chapter. All the calculations are accomplished with simple, grade school math using an inexpensive calculator and basic plotting tools. If you believe you do not need these Old Time navigational skills in this modern age of electronic navigation, Captain Jack restates his suggestion to you: "Tape a mirror below your GPS display. When the electronics fail, you can look in the mirror and see exactly who is lost."

About this title

From the Author

With the incredible advances in electronic navigation equipment, especially the development of the satellite system, small boat navigation is so simple I'm surprised anyone would make the effort to learn basic navigation.

The greater effort of learning celestial navigation, I thought, would be an effort that would go the way of the dinosaurs. To my surprise basic navigation is in good demand and I have more requests for classes in celestial than ever before.

There remains a fear the electronics may fail. To a greater extent my students want the security that comes with knowledge and in the case of celestial, they want the bragging rights. Very few sailors ever get far enough along with the study of celestial navigation for it to be useful to them. Most sailors at a yacht club bar will begin to fade away when a few sailors start talking about reducing sights, cocked hat star sights, etc.

Before the electronics age, most long-range sailors who claimed to know celestial navigation, only understood the "noon sight." As you will learn the noon sight is a very small part that can be learned by almost anyone in a matter of minutes.

When I decided to go cruising, I knew I had to learn celestial because the only electronic aid available at the time was the old Loran A, a huge, expensive instrument, which I knew I couldn't afford on my limited budget.

I read that people would sit on the end of a dock and learn celestial from a boat neighbor, but I didn't know anyone who knew celestial. In one sailing magazine story a new sailor picked up a book on celestial navigation and after a few hours reading was qualified to go around the world using his sextant. If it's that easy why don't I just dig in and learn? I tried not one, but several books on the subject and after many days of reading had not learned anything. During the fifth book the light finally penetrated my thick skull and I started to enjoy the learning experience. Many more days went by before I could honestly say, "I understand."

After arriving at this understanding, I spent several months getting the boat ready to go. Shortly before it was "cast off" time, I realized I couldn't remember enough celestial navigation to work a sight. To my chagrin it was almost as hard to relearn celestial navigation as it was to learn it in the first place.

Finally, all came together and I began my cruising life, with my celestial navigation working very well. This sort of life came down to a few days of sailing and weeks of hanging on the hook, gunkholing and exploring, amounting to nothing more than coast piloting. When it was time for the second leg of my cruise, I had forgotten celestial again.

All in all, I probably relearned celestial navigation six times, with each time being virtually as difficult as the first time. It wasn't until I agreed to teach celestial navigation to a group of my sailing buddies that I got the material organized well, thereby getting it straight in my mind. Using this organization as a technique in the class room I find my students are better able to remember what they learn. Part of this technique involves NOT using preprinted forms. With forms, the student is learning how to fill out forms and retains very little of the purpose behind the procedure. If the navigator addicted to forms runs out of forms or -- God forbid -- they get blown overboard or soaked with sea water, then he is no longer able to find his way. That would be no different than having a GPS with dead batteries.

Please understand my methods are not necessarily scientific perfection. They are more of a method for you to find your way with a sextant, reducing the sights on the back of a matchbook while leaning against the mast, if it is ever necessary to do so.

Jack I. Davis

Excerpt. © Reprinted by permission. All rights reserved.

From Chapter 1:

The sextant will measure the height above the horizon of a celestial object, (sun, moon, planet or star), in degrees, minutes and fractions of a minute. Some sextants show seconds instead of a fraction of a minute.

What good is this to us? How does this help us find our position? To demonstrate, let's look at Polaris, the North Star.

Our latitude in Southeast Texas is about 30 degrees North. When we use our sextant to shoot a sight of Polaris we face north and find the star is about 30 degrees above the horizon. If we were in Nebraska, our latitude would be about 45 degrees North and facing north our sextant would show Polaris to be 45 degrees above the horizon. In fact if we move all the way north to the North Pole we would be at 90 degrees North latitude and our sextant would read 90 degrees height for Polaris, regardless of which direction we faced.

Therefore, we can determine our latitude by measuring the altitude of Polaris.

We can determine the distance we are away from the North Pole, by measuring the height of Polaris. The point directly below a celestial object is called the GP. The GP of Polaris "wobbles" around the North Pole every twenty-four hours, so a sextant reading at dusk will be slightly off, as will a morning reading. An average of the two readings will be exact since the morning error and the evening error offset. The nautical almanac gives corrections for both.

POLARIS

How to find it

EQUATOR TO POLE

If a sextant reading is 30 degrees, subtract that from 90 degrees, which gives the co-altitude of Polaris. In this example, that would be 60 degrees. Since each degree is equal to 60 nautical miles distance, 60 degrees times 60 miles equals 3600 miles, the distance from the North Pole.

Co-altitude x 60 miles = 3D distance away. Figure 1-1 Jack Davis

The early ocean navigators understood that you could find your latitude using the North Star.

They didn't have the very accurate sextants we have today. They had a crude instrument called an astrolabe, which would give them a rough reading. When Columbus discovered the entrance to San Juan Harbor, Puerto Rico, he knew (from the astrolabe) the entrance was at about 19 degrees North latitude. He didn't have a clue what his longitude was and for his purposes it didn't matter.

When he sailed back toward his home port, he sailed north until he arrived at the latitude of the Mediterranean entrance. There, he turned east and ran that latitude line until the Rock of Gibraltar came into view.

On his return trip to San Juan, he sailed from the Mediterranean, past the Rock of Gibraltar and sailed south to 19 degrees North. He followed that latitude line until Puerto Rico came into view.

The thousands of sailors who followed in Columbus's wake, said when leaving the Mediterranean to go to the West Indies, you sail south until the butter melts, then turn right.

This "latitude sailing" has been used by sailors (and aviators) well into the electronic age and in fact I still use the technique on occasion.

Edition details

• Publisher: Bristol Fashion Publications,US
• Publication date: 1999
• Language: English
• ISBN 10: 1892216183
• ISBN 13: 9781892216182
• Binding: Paperback
• Number of pages: 152