Now lay these two Bearings off from C, cutting the line A B in the points a and b, see small Chart, p. 84. Next take 11 miles with a pair of dividers from the graduated Meridian and lay off from a towards b, and the point to which they extend call d. Through d draw a line parallel to the line of first Bearing, and where this parallel line cuts the line of second Bearing is the ship's position at the time of taking the second Bearing. The ship's distance from C will be found to be 20 miles, and the ship's Latitude to be 47° 16′ N., and her Longitude 44′ W. ANSWER-Latitude 47° 16' N. Longitude-44' W. Additional for Masters. IV. Find the Course to steer by Compass from A to B (see question 1) to counteract the effect of a current which set W. by S. (true) at the rate of 4 miles per hour, the ship making by log 7 miles per hour; also the distance the ship would then make good in 5 hours towards B. Directions.-Lay off from A the true set of the current W. by S., and on it measure 20 miles from A to represent the setting and drift of the current, call this line Aa, see Small Chart, p. 84. Then with a pair of dividers take from the graduated Meridian 35 miles, which is the distance the ship runs in 5 hours by the log. Place one leg of the dividers on a, and lay the other towards the line A B, and where the dividers meet the line A B, make a mark and call the mark c. Lay the parallel rules over a c, and bringing them in the usual way to the centre of the compass, we find N. W. true. Then proceed thus: True Course...... N. W. or N. 2° 49′ W. Therefore the course to steer from A to B to counteract the effect of the current, is N. 34° 11' E. The number of miles from A to c (38) is the distance made good towards B in 5 hours. ANSWER.-Compass Course N. 34° 11' E. h Distance 38 miles. V. 1884, March 29th at 2" 8m A.M., being off St. Ives, took a cast of the lead, required the correction to be applied to the depth by lead before comparing with soundings on Chart. Directions. From the Admiralty Tide Tables for 1884, find the times of high water at St. Ives in the usual way, which gives 5h 58m A.M. and 6" 19" P.M. The time of sounding being nearer to the A.M. tide, that tide is selected. We next proceed to find the "Height Constant." This must be done by taking the difference between the Spring Rise at the Port of Reference (WESTON SUPER MARE) and spring Rise at ST. IVES. The spring Rise is found at page 154, that for the Spring Rise for Port is less than Spring Rise for Port of Reference. In the The lead was cast 3" 50" before high water. Admiralty Tide Tables, opposite the A.M. tide at WESTON SUPER MARE is 40ft 2in, which is the height of high water for that tide, from which subtract the "Height Constant." The result is the height of high water at St. Ives, from this subtract the half Spring Rise at St. Ives, the result, 13ft 8in. is the height of high water above half tide. Now enter Table B, page 98, of the Tide Tables, with the time of high water along the top, and the height above half tide at the side, and we obtain 5ft 9in to be subtracted from half Spring Rise at St. Ives, leaving 4ft 9in as the correction to be subtracted from the soundings obtained by the lead line. Table B can be dispensed with by following this rule. Double the time from high water, and if over 61, subtract from 12". Bring the result into degrees. Consider this a Course. Bring the height of high water above high tide into inches. Consider this as a Distance. Now enter Table II. (NORIE) with this course and distance and take out the D Lat. 693. Consider this as inches, and bring it into feet and inches, and we get 5ft, gin. as before. To be added or subtracted according as the time from high water is less or more than 3 hours. The work of the above example is as follows: From page 105 of the Admiralty Tide Tables we find for ST. IVES. Tidal Constant 2h 10m WESTON-SUPER-MARE. From page 154 Spring Rise at WESTON-SUPER-Mare ST. IVES Difference h. m. 37 O 21 O 16 ft. in. (Candidates for Master's Certificates will be required to write the answers to the following Questions.) VI.-What do you understand those small numbers to indicate that you see placed on the chart ? Answer.—The depth of water in feet or fathoms at low water of ordinary spring tides. VII. What do the Roman numerals indicate that are occasionally seen near the coast and in harbours ? Answer. The time of high water at that place at full and change of the moon. VIII. How do you find the time of high water at any place, the Admiralty Tide Tables not being at hand, and no other special tables available? Answer. To the time of high water at full and change, add 49 minutes for every day elapsed since full or change; the result is the P.M. time of high water. Or thus :-To the time of the moon's meridian passage add the time of high water at full and change; the sum is the P.M. time of high water. EXAMPLES FOR PRACTICE. Notice. Before the candidate commences to work the papers C, H, J, K, L and M, he should make a fleur-de-lis on the N.N. W. W. point of the compass on the chart, and consider that point as Magnetic North, and all the other points dependent thereon. It would be advisable, therefore, to draw with red pencil a line, from N.N.W. W. to S.S.E. E., representing the Magnetic N. and S. line; also another red line, joining N. E. by E. & E., and S.W. by W. W., to represent the Magnetic E. and W. line. Having done this, proceed as in the worked examples, leaving out the Variation. (For Answers see end of book.) PAPER A (FOR TRUE Chart). Note.-The Variation in the following Examples is taken as 26° W.; at the Examination the Variation is found on the Chart given to the Candidate. 1. Find the compass course and distance from A to D. H 2. Ship's head on the above compass course, give the ship's position when B bore by compass N. 1810 W. and H bore by compass N 60° W. 3. Ship's head on the above compass course, F bore by compass N 10° W., ship then continued on the same course 12 miles, when F bore N 321° W. by compass. Find the ship's position and distance from F. 4. Find the course to steer in No. I question, in a current setting N. by W. (true) 2 miles per hour, the ship making by log 15 miles per hour, and find the distance made good in 3 hours towards D. 5. On October 22nd, 1884, at 7h 49m A.M., being off Heligoland, took a cast of the lead, required the correction to be applied before comparing with soundings. PAPER B. (FOR TRUE CHart). 1. Find the compass course and distance from C to D. 2. Ship's head on the above compass course, give the ship's position when B bore by compass N 51° E. and S bore by compass S 70° W. 3. Ship's head on the above compass course, A bore by compass S 171° E., ship then continued on the same course 12 miles, when A bore by compass S 300 W., find the ship's position and the distance from A. 4. Find the course to steer in No. I question, in a current setting North (true) 4'5 miles per hour, the ship making by log 12 miles per hour, and find the distance made good in 4 hours towards D. 5. On January 9th, 1884, at 4" 12" P.M., being off Brest, took a cast of the lead, required the correction to be applied before comparing with soundings. |