The Complete Ocean Skipper: Deep-water Voyaging, Navigation and Yacht Management by Tom Cunliffe

Author:Tom Cunliffe [Cunliffe, Tom]
Language: eng
Format: epub
ISBN: 9781472918147
Publisher: Bloomsbury Publishing
Published: 2016-04-14T07:00:00+00:00

Maximum altitudes

In theory, this system for determining latitude only works perfectly from a stationary vessel, or one travelling exactly east or west. This is because if you are in the northern hemisphere and sailing southwards towards the sun (your latitude being greater than its declination), your changing latitude causes it to go on rising even after it has passed your meridian. The converse holds true sailing north.

For a big ocean racer logging 20 knots or more due north or south, the errors thus generated can be at least five minutes of arc. Aboard a cruising boat struggling to maintain six knots it is rarely a factor to consider, but with a significant north/south component in the course it should not be forgotten because your latitude from a meridian sight may not be quite as accurate as you might otherwise hope.

ALLOWING FOR THE MAXIMUM ALTITUDE EFFECT

Since the sun is crossing one meridian every four minutes, you should be able to work out the time that the sun will pass your noon DR to the nearest minute or two. If you are careering toward or away from the poles, more or less, shoot the sun’s altitude at about this time instead of waiting for it to reach its highest point. You’ll then have given it what you might call your best shot. In any case, so close to noon, the altitude will be changing very slowly, if at all.

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