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post #6 of Old 08-21-2011
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You seem to understand the problem from your OP, and are simply trying to decide what to plot.

Seems to me the problem unfolds this way: If the logbook entries are 004M and 264M, they were taken from the compass. Doesn't have to be that way, but generally, the compass is your most reliable heading instrument. Could have the GPS display in magnetic, or the chart plotter, but you can get fix right off the display if you have good signal, and that makes no sense for the stated problem. If you are manually plotting, as the post sez, and leeway is known (how? as a known characteristic of the vessel when it is hard on the wind in 18 knots, which is the only way I can think of unless you are comparing compass heading against course on the GPS), then DR would be plotted along the mag course 004, and EP would be plotted at the end of a vector from your starting point along mag direction 009, at a distance equal to your estimate of distance traveled from the starting point.

When you tack to 264M, plot your DR along the 264M course from your 1400 DR position.

When you get a fix, reset your position to that fix, evaluating its quality, and start a new DR from that fix.

Dead reckoning is a simple integrated plot of course using the instrument you steer by and the speed you read on your log. Estimated positions include leeway, current effects not measured but historically observed, and other factors.
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