Mirelle
N/A
Vertical angle
Vertical angle is the easiest, and one of the most accurate, ways of getting a position line. There is a table in the Almanac (or should be, if not, you need a book of tables) which was first drawn up by the legendary STS Lecky. Any coastal feature whose height above HW is known can be used - bring its top down to the waterline and enter the tables with the angle read from the sextant and the height, corrected for tide if you want to be really accurate. The answer is your distance off, accurate to a few yards. If you need to keep a certain distance clear of a headland or mark, set the sextant to the angle in question, then pick it up and glance at the headland from time to time as you pass - this is even easier than using GPS! That's why charts show heights of lighthouses, nuclear power stations, churches, hills and so on.
Vertical angle is the easiest, and one of the most accurate, ways of getting a position line. There is a table in the Almanac (or should be, if not, you need a book of tables) which was first drawn up by the legendary STS Lecky. Any coastal feature whose height above HW is known can be used - bring its top down to the waterline and enter the tables with the angle read from the sextant and the height, corrected for tide if you want to be really accurate. The answer is your distance off, accurate to a few yards. If you need to keep a certain distance clear of a headland or mark, set the sextant to the angle in question, then pick it up and glance at the headland from time to time as you pass - this is even easier than using GPS! That's why charts show heights of lighthouses, nuclear power stations, churches, hills and so on.