TO READ THE LOG. The indicator of the patent log has three dials, on the same principle as a gas-meter. The first dial is marked in quarters (representing one-fourth of a mile); and the second dial is marked in even miles, and records as high as 10; while the third is marked to 100 miles in 10-mile divisions. When the ship has sailed 100 miles, the three hands will all point at zero, and then commence again their regular revolutions. LEEWAY. HOW TO DETERMINE IT AND ALLOW IT TO A SHIP'S COURSE. When a ship is sailing with the wind on her beam, she will be also forced sideways through the water while she is going ahead, and this can result from having sail set, or it can be occasioned by the vessel having a high freeboard, and the wind acting upon it and her top hamper (spars, etc.) This sideway motion is termed "leeway," and its amount varies with the shape of the vessel, force of the wind, and amount of sail exposed (set). A very simple method for determining leeway is as follows: Observe the course the ship is heading, which we will call north; then as her keel is on the line of north and south, by observing the bearing of the wake over the stern we can see how much difference there is between it and the line of the keel, and that will be the leeway. Suppose that in this instance the wind was easterly, and the wake bore south-by-east. The ship is on the starboard tack, consequently the leeway is being made towards port, or the left-hand side. Now, instead of the ship making a north, she is making a north-by-west course, as she is being driven sideways sufficiently to make a point off her apparent course as shown by compass. If the patent log is being towed, its angle with the line of the keel can be readily seen, and the same will be the leeway. When working a traverse table, always correct the ship's courses for leeway (providing there has been any made), and then after this correction apply the variation of the compass for the latitude and longitude of the ship, which will be given on the chart, and the answer will be the true or geographical course that the ship has made. When a vessel is making leeway the wake will always be left to windward, but if the ship is making no leeway the wake will be left dead astern. CURRENT SAILING. If a ship has been sailing in a current (as shown on chart), the direction of its flow must be called a regular course made, whether with or against the vessel, and the velocity of the stream reckoned as a distance per hour for the time the ship was in it. For example: a ship has been crossing the Gulf Stream, and has been in the current twelve hours. Its flow where the ship crossed has been north-east, and its velocity two miles per hour. Make a note of this in the column of "Remarks," in the log-book, and, when working the traverse table, set down as a regular course north-east 24 miles, and this will allow for the north-east drift the ship has made while she has been heading another course by compass. Again, suppose a ship has been heading N.E. in the Gulf Stream where the current sets N.E. It is only necessary to add to the face of the log the amount of the current per hour for the time the ship was under its influence. If the ship has been heading against the Stream, simply deduct the value of the current per hour from the log for the length of time the ship was in it. This was fully explained under heading of the "Patent Log." ALLOWING FOR DRIFT WHEN HOVE-TO. When a vessel is "hove-to," she will "come up" and "fall off." Now the middle point between this coming up and falling off must be called the course of the ship, and the leeway and variation allowed from this middle point as usual. For example: a ship hove-to comes up to north, and falls off to north-west. The middle point is north-north-west, and the leeway and variation must be allowed from this point. Under such circumstances, a vessel makes a great deal of leeway, and care must be used to apply it correctly. No general rule can be given for allowing for leeway, as different vessels make different amounts. The officer of the watch must determine this for himself. When hove-to, the tiller is put over to leeward, and, when the ship gathers a little way, the rudder brings her up into the wind; she then loses her way in the water, and the rudder ceasing to act, she falls off; thus she is kept continually coming up and falling off. Every time she gathers a little steerageway she forges ahead, and this forging will amount anywhere from one to two knots per hour, according to the vessel and the circumstances. This speed must be allowed to her true course made. TAKING DEPARTURE* OR FAREWELL. After you have sailed away from the land a distance which will enable you to set your course, take the bearing of some well-known light or headland, judge the distance between your ship and the object, and make a note of this in the log-book in the column of "Remarks." This will be considered as the first course and distance sailed, and the opposite to the bearing the direction of the course, which will be set down on the traverse table, after correcting it for variation, the same as any regular course. For example: I take farewell, Sandy Hook Light bearing north-west, distant 10 miles. When working the traverse table for my first day's work, I take as a first course the opposite to north-west, which is south-east, and correct it for variation, and opposite place the distance previously noted-10 miles. The latitude and longitude of Sandy Hook being my point of farewell, this course and distance must be allowed the same as a regular course sailed, so as to determine the distance of the ship from the land left, when the first course was set. *The word "Farewell" should be used in preference to "Departure," so as not to confound the expression with the departure (easting and westing) calculated by traverse table. The CHRONOMETER is simply an accurate time keeper, or clock (regulatedto Greenwich time) which is swung in gimbals like a compass, so that it may preserve its equilibrium when the ship plunges and rolls. Before a chronometer is sent aboard ship by the dealers, its daily variation (rate) from the mean time of the place is observed, and a memorandum, called a "rate-paper," is sent with the instrument, informing the ship-master as to the chronometer's present standing error, and to allow so much to the face of the chronometer daily; to add or to subtract such an amount each day until the chronometer is returned to them. For instance: suppose when a chronometer is received on board ship, the rate paper accompanying same should inform the receiver that the chronometer No. 1000 was on the given day 1' fast of Greenwich mean time, and that its rate was a daily gain of 5 tenths of a second. This paper would be preserved, and for every day thereafter one half second would be added to the rate account, and the whole deducted from the chronometer's face when working an observation. In the small nautical almanacs, furnished gratuitously by the various nautical warehouses, are columns adapted for the keeping of the chronometer rate, and to make the explanation complete, an entire page showing the method will be found following, in which the instrument has been received on February 10, showing it to be slow of Greenwich mean time 5 minutes, 10 seconds and 5 tenths, with a losing rate of 9 tenths daily. On the 15th of the month an observation is taken, and the error of the chronometer as calculated is 5 minutes, 15 seconds and no tenths. This will be added to the face of the chronometer, owing to loss by the chronometer running slow. It will be seen by reference to the columns that the 9 tenths are added mentally, day by day, and the whole error for the given day can thus be selected at a glance, without the nuisance of footing a line of daily variations. |