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Author Topic: Is an artificial horizon useful for cel nav practice?
 David Burch posted February 08, 2006 03:35 PM                   You can indeed use a pan of oil or even a well-leveled plate glass mirror to take sights inland away from a true water horizon. If there is any breeze blowing, the surface must be covered with a piece of plate glass. Any ripples at all will disturb the process. Explorers used this method since early this century in the Arctic and in the desert (generally with small trays of mercury). For practicing the marine application of celestial navigation, however, this is not a very useful method. We do not recommend it for several reasons. First, it is not done like a normal sight. You look down at the pan, not straight out toward the horizon, and you align the objects for a sight in a different manner than done at sea. You must then sight reduce the data in a different manner than normally done. Also you are limited to only one half the range of the sky since the process doubles the altitude. In short, you are not getting practice with what you will actually be doing underway. You are just getting data that might be about right to practice sight reduction with. We can assure you, however, that celestial works, and doing the textbook practice exercises will do this job just as well as generating numbers this way. Furthermore, if you have any water at all around (a lake, or bay, or even river) that is a quarter of a mile or so across, then you can practice with the "dip short" method using the shoreline. This is a much more realistic way to practice. The method is described in detail in Chapter 2 of our course, or see discussion in Bowditch. This is not only a good way to practice, it is a technique that you might indeed need one day. Also if the distance (in nautical miles) across the body of water is equal or greater than the square root of your height of eye (in feet) above the surface, then you are looking at the true curvature of the horizon, not the actual shoreline, and do not even need to use the dip short correction. In summary, if you have any water at all around you, you are better off using it rather than a so called artificial horizon.With that said, we do indeed cover the method in detail in our cel nav course. From: Starpath, Seattle, WA

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