|Boy's Manual of Seamanship and Gunnery|
Log Line - Log Ship
Q. Describe a log line ?
A. The first part of the line is called stray line ; a piece of buntin marks the end of the stray line ; the marking of the line commences from the piece of buntin, and is equally divided into parts, called knots and half-knots, and is marked thus :- 47 ft. 3 ins. from the buntin which terminates the stray line, a piece of leather is put, which denotes the first knot or mile ; thus at every 47 ft. 3 ins., knots are put to denote the number of miles or knots, from two knots up to the required number, the line being marked according to the highest rate of speed the ship is expected to go ; between every knot there is what is termed a half-knot, which is a single knot.
Q. How does the log line so marked denote the speed of a ship ?
A. Two log glasses are used in conjunction with the log line, called the long and short log glasses. The long glass is a 28-sec. and the short one a 14-sec. glass.
The long glass is used when the ship is supposed to be going less than five knots through the water, and the short glass when her speed is greater.
The division of knots on the log line bears the same proportion to a nautical mile as the log glasses do to an hour.
For example: If the long glass is being used, and three knots run out, the ship is going at the rate of three knots an hour; if the short glass is being used, she is going six knots an hour ; if the one knot between the three and four knots, with the short glass, it will denote that the ship is going seven knots ; if the long glass, three and a half knots.
Q. What is the use of stray line, and what length ought it to be ?
A. It takes the log ship out of the influence of the eddy water in the ship's wake, and also allows it to get a good hold of the water, before the whole of the stray line is out, and the marking of the ship's way through the water is began.
The length of the line should be rather more than the length of the ship.
Q. How is a log ship attached to a log line ?
A. By three pieces of line called legs, two being spliced into the log line, the end of the log line forming the third.
There are three holes in the log ship ; one in the upper or pointed part, the other two at the opposite extremes of the log ship, just above the circular part ; through one of these, and the hole in the upper part, two of the legs are rove and knotted to keep them in place, the other leg has a peg of hard wood or bone spliced in it, and when the log ship is in use, it is put into the remaining hole of the log ship. When the log ship is thrown into the water, being slung in this way, it swims in an upright position, the lower, or arc part, being weighted, catches the water and remains stationary, and . the ship moves ahead away from it, the line which is kept on a reel runs out, the reel being held in a position to facilitate its movements.
A knot is divided into ten parts, but not so marked on the line, the person heaving the log judging according to the length of line out. For instance, a ship is said to be going 4 and 2, 4 and 6, 4 and 8, according to the length of line run out between the knot and half-knot.
Q. How is the log hove ?
A. The person that heaves the log stands as near the lee quarter as possible, inserts the peg in the hole of the log ship, takes several fakes of' the line in one hand, to insure sufficient slack line to allow the log ship to fall clear into the water, holding, the lug ship in the other, sees the reel is held in a good position, and then asks the question, " Is the glass clear ? " which is answered by the person holding the glass (which is generally the quartermaster of the watch), "a clear gloss. "
The log ship is then dropped into the water and floats astern, care being taken that the line is not checked ; when the piece of buntin marking the stray line passes through the hand of the person heaving the log, or over the quarter, he calls out " turn, " which is answered by the person holding the glass saying " turn, " attending the line that it runs out freely, occasionally assisting it by a slight tug.
The person holding the glass, when all the sand has run out, calls out " stop, " when the line is instantly checked, and the nearest knot is looked for, which denotes the rate the ship is going.
Directly a strain is brought on the line, the peg slips out, and the log ship floats on its flat in the water, in which position it offers no resistance, and is easily hauled in.
Should the peg stick fast in the hole, it is very difficult to haul the log ship in, and it often carries the line away; therefore care should be taken not to jamb the peg in too tightly.
Q. Who heaves the log?
A. The midshipman of the watch.
Q. How often is it hove?
A. Every hour, and the result noted in the log book.
Q. What difference is there between a nautical and a land mile ?
A. A nautical mile contains 2027 yards, whereas a land mile is only 1760 yards.
Q. What is the cause of this difference ?
A. A land mile is measured without any reference to the size of the earth.
A nautical mile is the number of yards contained in the circumference of the earth at the equator, divided by 21600 (360° x 60), the number of minutes in a circle, or the sixtieth part of a degree on the equator.
Q. Is there any other mode of finding out the speed of a ship, or the distance run by her in any given time ?
A. Yes; Massey's patent log, which is considered the most accurate way of measuring the distance run by a ship.
Q. How is it used ?
A. It is bent to the end of a deep-sea lead line, and veered about forty or fifty fathoms astern, generally from one of the weather quarter boats, which takes it to windward, and well out of the influence of the eddy water in the ship's wake.
Q. What does it consist of?
A. An indicator, with three dials, one marked in divisions of 10 up to 100 miles, the second marked in divisions of miles up to 10 miles, and the third marked in four quarters of a mile.
Thus the last dial denotes the quarters ; the second dial, the miles up to 10 ; and the first shows the 10 ; that is, whether it is 47 ½ or 56 ¾ miles.
For example - If the ship has run 47 ½ miles, one dial will mark 40, the next dial 7, and the next dial half a mile, which, by adding the three together, gives the distance run as 47 ½ miles, so on up to any distance under 110 miles.
The log is usually hauled in at the end of each watch, and the result registered in the ship's log book.
A fan is attached by a piece of cord to the after end of the indicator, and as the ship moves through the water, the fan is turned by the action of the water, which motion is communicated to the wheel, worked by means of the piece of cord which connects the face to the indicator.
On the fore end of the indicator a piece of iron rod is attached also by means of apiece of cord ; just abaft the hole for the cord are two iron studs through the iron rod, crossing each other at right angles.
In the after end of the rod is a hole for bending the end of the deep-sea lead line to, which is bent in a similar way that it is bent to the becket of a lead.
Q. What advantage has the patent log over the common log?
A. Very often the wind is uncertain : at one part of the hour blowing a fresh breeze, at another nearly a calm ; the common log merely shows what the ship is going at the time it is hove, and the officer of the watch judges what in his opinion the ship has really made, which of course is liable to error, whereas the patent log shows the exact distance the ship has run, whether it has blown fresh one part, and the ship has gone at the rate of ten knots, and at another part of the watch it has been nearly a calm, and she has scarcely moved through the water, still the true result is shown.
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