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    Re: Approaching A Destination by Latitude Line Sailing
    From: Frank Reed
    Date: 2014 Apr 5, 17:16 -0700

    Brad Morris, in reply to Gary's post, you wrote:
    "I was thinking of the approach to a larger land mass. For example, sailing to NYC from England. Its hard to miss the continent, but its easy to end up either to the north or south of NYC.
    The approach you detailed is entirely correct for a small island. "

    I think it's pretty clear now that Brad has gotten two concepts confused. Latitude sailing is one thing. It's the process of getting oneself into the latitude of one's destination because the longitude is suspect. At some distance off, you get into the latitude of the destination and then, so long as your able to confirm that latitude by observations, you will bump into your destination by sailing east-west along that latitude. That's latitude sailing. And it's the same thing that Thoms was writing about c.1850 in the pages posted by Henry Halboth. Naturally, except in emergency circumstances, this was relevant only in the era before chronometers became reliable. Latitude sailing was largely over and done with by the middle of the 19th century. The second concept, which Brad has confused with latitude sailing, is a landfall procedure (which Gary LaPook has described in a number of posts with respect to air navigation, especially). This is the process of aiming to the left (an arbitrary choice for this discussion) of one's destination when that destination is found on a linear feature, like a coastline or a river, which is mostly perpendicular to the direction of travel. The idea here is that by intentionally aiming to the left of the target point, then when the coastline (or other linear feature) is reached, we know to turn right and follow the coast and we will most likely run into our destination in that direction. Note that this procedure might be called upon whenever there is any cross-track uncertainty in position no matter what direction we're travelling. This is NOT latitude sailing.

    Note that neither latitude sailing nor the above targeting trick are related in any way to Greg's original question about latitude by meridian altitudes of stars observed with an artificial horizon, nor are they connected with the accuracy of latitudes determined by meridian sights using any instruments from the mid-18th century onward. Hence, as I pointed out originally, this was all just a non sequitur. As I said, it literally has "absolutely nothing" to do with Greg's question or any of the issues that question raised.


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