## Refraction Error Correction in Sextant Measurements

Refraction is probably the most difficult to understand of all the altitude observation corrections. It is also the most difficult to estimate accurately because it depends so strongly on atmospheric conditions, particularly the rate of temperature variation with altitude (see lapse rate). I will derive in this post a commonly used expression for the refraction correction required for a celestial object with an altitude greater than or equal to 15°. The accuracy of this expression degrades significantly for objects below 15°. Continue reading

## Correcting for Sextant Parallax Error

Navigators use the altitudes of solar system objects to assist them with determining their positions. The most commonly used solar system objects are the Sun, Moon, Venus, and Mars. There is a small error caused by the fact that navigators are making their sextant measurements from the surface of the ocean and not from the center of the Earth, which is the reference point used by nautical almanacs. Parallax has no practical significance when measuring the positions of stars because they are so far away relative to the radius of the Earth. Continue reading

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## Correcting Sextant Measurements For Dip

I love to read stories of the sea and about the voyages made during the age of sail. I personally have never thought that I would have an opportunity for ocean sailing, but I recently began working with an engineer who is an avid sailor and teacher of sailing. He has sailed all over the world and recently trained another engineer in my group to sail. This newly trained sailor just returned from a trip to Bora Bora, which he found to be enjoyable and the sailing uneventful. Continue reading

## Compensating GPS Clocks for the Effects of Relativity

I occasionally read articles on Stumbleupon and I came across an interesting article called "8 shocking things we learned from Stephen Hawking's book" – the book they are referring to is called "The Grand Design". I personally would not call the statements in the article shocking, but that is just my opinion. Continue reading

## Computing a Ship's Course from Four Bearings

I have made no secret of my love for all things nautical – even my game playing has a nautical theme. When I have spare time, I like to play Silent Hunter 3 or 4. While these are older versions of the Silent Hunter franchise, I still enjoy playing them very much. What brings me back to Silent Hunter is how easily I can vary the level of realism to suite my gaming needs. Continue reading

## Ship's Course Correction for Cross-Current Rule of Thumb

I have lived most of my life in Minnesota, which is about as far away from the oceans as you can be in the United States. The idea of a planet mainly covered with water has always fascinated me. I will never forget the first time I saw an ocean (Pacific, Santa Monica, CA 1982). Fortunately, my work has provided me a bit of experience on ships and that experience was career changing − my early ocean experience involved laying fiber optic cable and that set the course of the rest of my career. Continue reading

## Sub Missile Launch Physical Model

I like it when instructors use physical models to illustrate how things work. I was watching this video on submarine design when I saw a physical model used to illustrate how a submarine launches a missile. The demonstration is excellent. … Continue reading

## Submarine Fuel Math

Introduction I just read an interesting article about an arctic environmental problem being presented by a Soviet-era nuclear submarine that had been scuttled back in 1982 (Figure 1). Apparently, scientists are now concerned that the submarine's reactor could leak dangerous … Continue reading