Note. You could have solved this day's work without correcting the courses seriatim for variation, by merely correcting for leeway as it occurred, and then making one correction for variation;—by this process you would have got— Diff. Lat. 61-2' N. and Dep. 88-2' W. From these, the resulting Course and Dist. would be N. 55 W. 107 miles. This Course corrected for 2 points, or 2210, Westerly variation, to the left, would become N. 78° W. and Dist. 107 m. Then, the newly corrected Course and Dist. would, by entering Trav. Tab. 5, give the correct Diff. Lat. and Dep. as in the worked example. You can now take the following day's work; it is prepared for construction, but I will also give you the results by inspection. By Inspection.-Diff. Lat. 52.2' S.; Dep. 100.3 W.; Course S. 621° W. Dist. 113 m.; Lat. in 44° 48′ N.; Diff. Long. 142'; Long. in 12° 27′ W. H. 10 5 11 5 5 Leeway. 1 S. 23 2317∞∞ 10 23 7721 3 3 3 7 W. W. N. W.IN. 667777GG GO TO 10 10+ ∞ ∞ ∞ ∞ 2222 123456789 7 Variable W. N. S.S.W. W. W.N.W. Variable Remarks. 2 P.M. Moderate breeze and fine weather. 3 P.M. Increasing, and squally. 5 P.M. Fresh breeze with heavy sea from the south. Current assumed to be mile per hour for the 24 hours, setting S. A.M. Light airs and fine weather. Course. Diff. Latitude N. Diff. Longitude W. Bearing Acc. Obs. Long. Acc. Obs. of S.621 W 113 52 100 44° 48' 142 12° 27' Traverse Table constructed from the above Log-board, with the Courses corrected for Leeway, and their respective Distances made good. Note. In the Remarks, the current was setting S., that is, was carrying the vessel to the S., the effect of which is here put down as a S. course, distance 12 knots or miles, as it was affecting the ship's course half a mile per hour during the twenty-four. The compartments at the foot of the log are appropriated to the result arrived at from the working off the Traverse Table, which the learner should now also work out, and compare the correctness of his solution with the one here given. TO TAKE A DEPARTURE. The bearing of the last headland likely to be seen from the ship is to be taken from two points, and the distance between these points is to be carefully noted by means of the log-line or patent log, and also the ship's course, until the headland nearly ceases to be seen. W., N. until Ex. At 3 P.M. the Lizard bore N. b W. and having sailed 7 knots an hour W. 5 N. 6 P.m., the Lizard bore N.E. E. What is its distance from the ship? By Construction.—Draw the compass, and let its centre be the ship's place at the first observation, and from it draw a line of any convenient length in the direction of the ship's course: also from the centre draw a line of any length of the same compass bearing as the headland when first observed. From the centre also draw a line of the same bearing as the headland when last seen. On the line of the ship's course prick off the distance made good, and at this point draw a line parallel to the last bearing that was taken, until it cuts the first line of bearing, at which spot the head land will now be supposed to be placed, and the measure of this last line drawn will give its distance (see fig. 5). a C FIG. 5. Here c 1 is the bearing of the Lizard from the ship at the first observation, c 2 is the course sailed, c 3 is the bearing of the Lizard at the last observation; c a is taken to equal 21 miles (the run of the ship). From a we draw a b parallel to c 3; a b is the distance of the Lizard from the ship at the last observation, and is equal to 19 miles. In working off the log, the ship is now to be supposed to have set sail from close in with the Lizard, and this is to be entered as the first course and distance; and as the centre of our drawn compass will represent the Lizard Point, which last bore N.E. E. from the ship, a line diametrically opposite to this must be drawn, viz. S.W. W., and 19 miles measured on it; so that the first course of our Traverse Table will be—course S.W. W., distance 19 miles, and our latitude and longitude left will be that of the Lizard Point. Note. I now give the general rule for the solution by Inspection, which is the best method:— Rule.—By Inspection:—When the angle between the first bearing and the course is more or less than 8 points. Enter Trav. Tab. with the angle between the first Bearing and the Course as a Course, and the Dist. run (in Dist. col.), opposite which take out the Dep. Then, enter Trav. Tab. again, with the Diff. of Bearings as a Course, and the Dep. (just found) in Dep. col. ; the Distance of the object at the time of taking the second Bearing will be found in the Dist. col. N.B.—If the angle is more than 8 points (or 90°) take its supplement; i.e. subtract it from 16 points (or 180°), and enter the Trav. Tab. with this difference as a Course. Also note the following rule: Rule.-By Inspection :-When the angle between the first bearing and the course is 8 points, the distance at either bearing is readily determined by inspection from the Traverse Table, thus:— Enter Trav. Tab. with the Diff. of Bearings as a Course, and the Dist. run in Dep. column; then the Dist. column gives the Distance of the object at the time of taking the last bearing; and the Lat. column gives the Distance of the object when the first bearing was taken. Ex. Cape Clear bore N., and after running W. 7 miles it bore N.E. 1⁄2 N.; find the distance at the last observation. Diff. of bearings, 3 points.) In Trav. Dist. 11 m. Hence by inspection, the dist. of the Cape was 11 miles from the position where the second bearing was taken; also 83 miles distant when the first bearing was observed. The learner is requested to make himself thoroughly conversant in working off the ship's place by Dead |