EXAMPLE 1.-A steamer steers N N E E by compass; wind E by S; variation 1 point E; deviation 2 points W; leeway estimated to point. Find the true course made good.

The dotted line at circumference of compass diagram, Fig. 8, shows the application of the various corrections in this example, the arrow indicating the direction of the wind.

S

EXAMPLE 5. – A steamer steers ESE by compass, variation 26° 45′ E, deviation 17° W; a strong wind is

-S 49°11′E

S 66°41'E

ESE

-S 75°56′E

FIG. 12

NOTE. - In the foregoing examples it will be noticed that the variation is applied first. In finding the true course from a given compass course, however, the deviation is usually applied first, thus obtaining the magnetic course, when variation applied to this will give the required true course; but this order is not an absolute necessity. The corrections may be applied in any order as long as they are applied in the proper way.

34. The student should bear in mind that in all problems of course corrections the deviation applied must be that of the compass course, no matter in what order the corrections are applied.

EXAMPLE 1.-A steamer steers S by W by compass; the variation, according to chart, is 12° E, and the deviation according to Table III. Find the true course. SOLUTION. - See Fig. 13.

Compass course = S by W

Or S 11° 15' W

Variation

=

-S 23°15'W

-S 37°15'W

W

True course = S 37° 15' W. Ans.

FIG. 13

EXAMPLE 2.-The compass course is E SE, wind is south, estimated leewaypoint, variation by chart 5° W, deviation according to Table III. Find the true course.

35. To find the compass course when the true course is known.

When it is required to find the course to be steered by compass in order to reach a port or position, the true bearing of which is known, the corrections must be applied in

exactly the opposite direction to that used in finding the true course from the compass course.

Rule. Apply leeway toward the direction of the wind, westerly variation and deviation to the right, and easterly variation and deviation to the left.

-True Course

N 30°E

-N 52°E

FIG. 14

EXAMPLE 2.-The true course, or bearing, between two places is N 10° W, variation 4° E, deviation according to Table III. Find the compass bearing.

36. In finding the compass course from the true course, the variation should always be applied first so as to obtain the magnetic course; the deviation corresponding to the magnetic course given in column 3 in Table III is then applied, the result being the compass course. In case the magnetic course does not agree with any of the values given in column 3, the deviation may be found by simple proportion; and, in cases where the deviation is small, it may be taken out for the value in column 3 corresponding most nearly to the magnetic course. With large deviations, the use of Napier's diagram is recommended as being a valuable aid for converting true courses into compass courses.

EXAMPLE 1.-The true course, according to the chart, from Fourteen Miles Point, Mich., to Grand Marais, Minn., is N 48° W; the mean

value of variation is 5° E. Use deviation from Table III and find the compass course.

SOLUTION. - See Fig. 15. True course = N 48° W

EXAMPLE 2.-According to the chart, the true course from Battle Island to Stannard Rock is S 8° E, mean value of variation 2° E, deviation according to Table III. Required the compass course.

EXAMPLE 3.- Required the compass course, having given true course N 8° W, variation 17° 10 W, deviation 3° 20′ E; the wind is easterly and the leeway estimated to

SOLUTION. - See Fig. 16.

point.