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If we apply the set and the drift of the tide to the 11:30 Dead Reckoning (DR) position, we will have converted this position to an 11:30 Estimated Position (EP).
To work out the set (direction) and the drift (speed) of the tide, we refer to the tidal diamonds on the nautical chart, or to the tidal stream atlas.
Let's assume that at that time the set is 110 degrees, which means that the direction of the tide is towards 110 degrees, and the drift is 3 knots.
To apply the set (direction) of the tide on the 11:30 Dead Reckoning (DR) position we place the parralel ruler on the 110 degree line of the compass rose and transfer that line to the DR position. To apply the drift (speed) of the tide on the 11:30 Dead Reckoning (DR) position to our time frame we use the formula:
D is equal to S times T divided by 60, where D is the distance in nautical miles, S is the tide speed, and T is the time in minutes.
In our case: 3 knots times 90 minutes divided by 60 equals 4.5 nautical miles.
Using the dividers, we span a distance of 4.5 miles on the latitude scale which is closest to the course line and which runs along the sides of the chart.
We apply this span, placing one leg of the dividers on the 11:30 DR position and the other leg on the 110 degrees tide set, marking the new position with a triangle, recording the time as 11:30.
This is our 11:30 Estimated Position (EP).
Using the parallel ruler, we transfer the 045 degrees course to the new 1130 Estimated Position, and from there we continue to plot our new positions as we progress on our route .
