(5.) When the true course between two places is known, it must be remembered that Westerly variation is allowed to the RIGHT, and Easterly to the LEFT hand of the true course, in order to obtain the COMPASS COURSE. (6.) With respect to the method of determining the ship's position by cross bearings, it may be observed that this is the most complete of all methods when the difference of bearings is near 90°; but if the difference is small-as, for example, less than 10° or 20°, or near 180°-the ship's position will be uncertain, because a small error in the bearing will cause a great error in the distance.—(Raper, page 120, No. 367.) EXERCISES ON THE CHART. FOR ONLY MATE, FIRST MATE, AND MASTER. (2.) (1.) Latitude 55° 5' N. Longitude o 5 E. Required the course and distance to Hartlepool. (3.) Latitude 53° 35' N. Longitude o 55 E. Required the course and distance to the Dudgeon Light. (5.) Latitude 60° 21' N. Longitude o 35 E. Required the course and distance to Udsire, (7.) Latitude 55° 28' N. Longitude o 30 W. Required the course and distance to Tynemouth Light. (9.) Required the true and magnetic Bearing and Distance between Whitby and the Naze of Norway. N N Latitude 57° 30' N. (11.) A ship from Kinnaird's Head, in Scotland, sailed S.E. by E. (true) 186 miles required the latitude and longitude she is come to, and the direct course and distance she must sail, in order to arrive at Heligoland. (12.) A ship from Heligoland sailed on a direct course between the North and West 197 miles, and spoke a ship which had run 170 miles on a direct course from Hartlepool: required the latitude and longitude of the place of meeting; also the course steered by each ship. (13.) N.W. "" ,, Sunderland Light, bearing by compass S.W. S. Coquet Island, Required the latitude and longitude of ship; also the course and distance to Hartlepool Light. (14.) Buchaness Light, N. by W. W., by compass. 99 Required the latitude and longitude of ship; also the course (by compass) and distance to the Staples. (15.) The Skerries North by compass. 99 Required the latitude and longitude in; also the compass course and distance to Peterhead. (16.) 99 Flambro' Head Light, S.W. by S. Whitby Lights N.W. by W. Required the latitude and longitude in; also the compass course and distance to Outer Dowsings (17.) Farn Lights, S.W, by S. by compass 99 Required the latitude and longitude; also the distance from each light. (18.) 99 Required the latitude and longitude of ship; also the compass course and distance to Flambro' Head. (19.) Scarbro' light was observed to bear S.W. by compass, then sailed E.S.E. II miles, and the light then bore West: required the latitude and longitude of the ship at each station, and her distance from the light. (20.) Coasting along shore, I observed Tynemouth light to bear W. by S. by compass; I then sailed S. by W. 16 miles, and the light bore N.W. by N.: required the latitude and longitude of the ship, and her distance from the light. English and Bristol Channels, and South Coast of Ireland. (2.) Latitude 50° 1' N. Latitude 48°50′ N. (1.) Required the compass course and distance to the Caskets. (3.) Latitude 49° 30' N. by compass W. Required the compass course and distance to Lundy Island. (15.) N.N.W. W. 99 Longships Light, bearing by compass E.N.E. St. Agnes' Light, Required the latitude and longitude in; also the compass course and distance to the Lizard. (16.) S.W. 99 "" Cape Barfleur, bearing by compass N.W. St. Marcouf, Required the latitude and longitude of ship; also the compass course and distance to Cape de la Heve. (17.) "" Bembridge Lightvessel, bearing by compass N. W. Owers Lightvessel, East. Required the latitude and longitude of ship; also the compass course and distance to St. Catherine's Point. (18.) Needles Light bearing by compass N. E. "" 99 St. Catherine's Light Required the latitude and longitude of ship; also the compass course and distance to St. Alban's Head. (19.) Caldy Island Light, bearing by compass E.N.E. S. by E. "9 Required the latitude and longitude of ship; also the compass course and distance to the Smalls (20.) Lizard Lights, bearing by compass E. S. "" 99 Longships, Required the latitude and longitude of ship; also the compass course and distance to St. Agnes' Light (21.) Mine Head Light, bearing by compass N.E. N. 99 "" Required the latitude and longitude of ship; also the compass course and distance to Old Head of Kinsale. (22.) Smalls Light, bearing by compass N. E. 99 99 St. Ann's (Milford Haven) Required the latitude and longitude of ship; also the compass course and distance to Seal Rock (Lundy Island). (23.) 99 Dungeness, bearing by compass N.E. by E. E. Beachy Head,, N.W. W. Required the latitude and longitude of the ship; and her distance from each place. (24.) A ship is bound to Boulogne, being 18 miles distant, and lying directly to windward, the wind being E, by N. (true). It is intended to reach her port on two boards, the first being on the port tack, and the ship can lie within six points of the wind: required the course and distance upon each tack. TO FIND THE COURSE TO STEER IN ORDER TO MAKE GOOD ANY COURSE IN A KNOWN CURRENT, AND ALSO THE DISTANCE MADE GOOD. Draw a line on a chart to represent the course to be made good; from the ship's place on the chart lay off a line in the direction of the set of the current, on which mark off from the ship's place the rate of the current per hour; then take in the compasses the distance the ship sails in an hour by log, and put one foot on the last-named mark, and from the point where the other foot reaches the first line draw a line to the mark on the line representing the direction of the current. The course to be steered is represented by the line last drawn, and the parallel ruler being placed to it, and moved to the centre of the compass on the chart, will give the course of the ship; and that portion of the first line drawn, intersected by the last line drawn, will be the distance the ship will make good per hour. On a chart, suppose A to be the place of the ship, B the port of destination; also A C the set of the current, the rate per hour being taken from the scale of miles and laid off in the direction of the line. Take the distance sailed by the ship per hour from the scale of miles, and with one foot of the dividers at C, make an arc cutting A at D. Join C D, and move the parallel ruler from C D to A, drawing A E parallel to CD: then A E will be the direction of the ship's head. And the parallel ruler being moved to the centre of the compass on the chart, will give the course of the ship on the chart; and A D will be the distance the ship will make good. LOG LINE. THE length of the stray-line should be sufficient to allow the log-chip to be clear of the eddies of the vessel's wake. The distance between the knots should bear the same proportion to the number of seconds run by the glass intended to be used, as the number of feet in a nautical mile bears to the number of seconds in an hour. The number of feet in a nautical mile is 6080. The number of seconds in an hour is 3600. Therefore, to find the length of a knot corresponding to a 28 seconds glass, we proceed as follows: We have for glasses running 30 seconds and 32 seconds the following proportions: 3600 6080:: 30: 50 feet 8 inches. 3600 MARKING THE LEAD LINE. In nautical phrase the lead line has "nine marks and eleven deeps." At two fathoms, the mark is leather; at three fathoms, leather; at five, white rag; at seven, red rag; at ten, a piece of leather with a hole in it; at thirteen, blue rag; fifteen, white rag; seventeen, the same as at seven; at twenty fathoms, a piece of cord with two knots. Deep-sea lead lines are marked the same as far as twenty fathoms; then add a piece of cord with an additional knot for every ten fathoms, and a strip of leather for every five fathoms. |