THE COMPASS-THE LEAD-THE LOG
THE COMPASS.-THE LEAD.-THE LOG.
The Compass– A piece of steel which has been touched by a magnet, if free to move on a pivot, will point in a definite direction. To this direction, as a standard, all others may be referred, and any desired course thus followed.
The Mariner’s Compass is based upon this principle. It consists of the needle, which is attached to the under side of a card, Fig. 1, representing the horizon, and graduated with the thirty-two “points” of the compass. The North end, or pole, of the needle is fixed under the North point of the card. The needle and card are balanced on a pivot fixed vertically in the compass-box, or bowl, and the whole is protected by a glass covering.
As the North mark of the compass-card always points with the needle to the North, the other marks will of course point to their respective parts of the horizon.
The variation of the compass and its local errors are not noticed here, as they may be referred to in any book on Navigation.
The Lubber’s Point is a vertical line drawn on the inside of the bowl of the compass to correspond with the vessel’s head; the point of the card coinciding with it shows the course steered, or the direction in which the ship is heading.
To Box the Compass is to name the points in regular succession, beginning at one point and ending at the same; thus, commencing with north and going around with the sun, say:-
A quarter-point (or half-point) can obviously be named with reference to either one of the nearest whole points. Thus N. 1/4 E. would be defined also as N. by E. 3/4 N., and E. N. E. 1/2 E. would be recognized as E. by N. 1/2 N.
The following are the usual rules for naming quarter-points:-
1st. From East or West to the nearest whole point, use for quarter-points that name which ends with the word North or South. Thus, E. 1/4 S., not E. by S. 3/4 E.
2d. From N. E., N. W., S. E., or S. W., to the nearest whole point use that name which ends with the nearest cardinal point. Thus, N. E. 1/2 N., not N. E. by N. 1/2 E.; N. W. 1/4 W., not N. W. by W. 3/4 N.
3d. In all other cases use that name of the quarter or half-point which ends with the word East or West. Thus, E. S. E. 1/2 E., not E. by S. 1/2 S.
A Dumb Compass is used at the mast-heads, taffrail, &c., for taking relative bearings. It consists of a compass-card painted on a board or cut on a copper plate.
Relative Bearings. In referring to the position of an object, the direction of the wind, &c., with reference to the ship, use is frequently made of what are called relative bearings, instead of giving the directions in compass-points.
|In Fig. 2 a ship is represented as heading North. A lighthouse or other object if seen bearing North would also be said to bear, from that ship: Ahead.If seen bearing N. by E.: One point on starboard bow.
Bearing N. N. E.: Two points on starboard bow.
Bearing N. E. by N.: Three points on starboard bow.
Bearing N. E.: Broad off starboard bow.
Bearing N. E. by E.: Three points forward of starboard beam.
Bearing E. N. E.: Two points forward of starboard beam.
Bearing E. by N.: One point forward of starboard beam.
Bearing East: Abeam.
Bearing E. by S. One point abaft starboard beam.
Bearing E. S. E.: Two points abaft starboard beam.
Bearing S. E. by E.: Three points abaft starboard beam.
Bearing S. E.: Broad off starboard quarter.
Bearing S. E, by S.: Three points on starboard quarter.
Bearing S. S. E.: Two points on starboard quarter.
Bearing S. by E.: One point on starboard quarter.
Bearing South: Astern.And similarly at N. by W., N. N. W. &c., one point on port bow, two points on port bow, &c., &c.
To find the direction of the wind, when ship is close hauled.-A square-rigged ship, when close hauled, can usually lie no nearer the wind than six points; therefore, if a ship be close hauled on the starboard tack, and her head at North, count six points thence to the right hand, or towards East, and you will find the wind at E. N.E. The wind then forms with the keel an angle of six points, so that if a line at Fig. 2, Plate 6, represents the ship’s keel, (c) will be the yard when braced up, and (d) the direction of the wind. In practice the yard is braced up sharper, to make the sail stand to better advantage.
When the ship is on the port tack with her head North, the points are counted on the opposite or left side, and the wind is W. N.W. If the ship’s head be put to any point of the compass, counting six points to the right or left hand, according. as the ship is on the starboard or port tack, will always give the direction of the wind when the vessel is close hauled.
When the wind is E. by N., in Fig. 2, the ship is then one point free, because her head is seven points from the wind. With the wind East in the figure, it is said to be two points free, or abeam, as shown in the remarks on relative bearings. If the wind is at S. in the figure, it is said to be aft.
After learning to box the compass with the sun, go around against the sun, or from North towards West, and practise with such questions as the following: Ship on the port tack, heading S. W. 3/4 W., how will she head on the other tack? With the wind at S.W. and steering due East,
|the ship is hauled up, two points and a half, how will she head? Close hauled, with the port tacks aboard, heading S. S.E., you bear up, keeping away six points, how will the ship head, and how will the wind be with reference to the ship’s beam? Ship heading N. N.E. on the starboard tack, a lighthouse is reported from aloft bearing two points abaft the lee beam, how will it bear by compass, &c., &c.?
Soundings, to ascertain the depth of water on entering or leaving a port, or in any case where there is supposed to be less than twenty fathoms of water, are taken by the hand lead, Fig. 3, a quartermaster or forecastle-man being stationed in the main chains for the purpose; the lead weighing, from seven to fourteen pounds, and the line being from twenty. to thirty fathoms in length. Hand lead lines are marked as follows:
At 2 fathoms from the lead, with 2 strips of leather.
These are known as the “marks.” The numbers omitted, as 1, 4, 6, 8, &c., are called the “deeps,” and they are spoken of together as the “marks and deeps of the lead line.”
All lead lines should be marked when wet.
Soundings by the hand-lead are taken while the vessel has headway on, the leadsman throwing the lead forward, and getting the depth as the vessel passes, while the line is nearly perpendicular. He communicates to the officer the soundings obtained, thus:
If the depth corresponds with either of the above marks, he says, “By the mark 5 or 7. If the mark is a little below the surface, he says, “Mark under water 5 or 7.” If the depth is greater, or one half more than any of the marks, he says, “And a quarter,” or “And a half 5 or 7.” If the depth is a quarter less, he says, “Quarter less 5 or 7.” If he judges by the distance between any two of the marks
|that the depth of water is 4, 6, 8, 9, 11, 12, 14, 16, 18, 19, or 21 fathoms, he says, “By the deep 4,” &c.On the hand-lead line there are nine “marks” and eleven “deeps.”Require the soundings to be given in a sharp, clear and decided tone of voice. In steamers, this is certainly the best plan, for while the old-fashioned “song” is being drawled out, the vessel may run ashore.
The Breast-band or Rope, generally the former, made of canvas, secured at both ends to the rigging, supports the body of the leadsman while heaving the hand-lead.
Besides the breast-band, it is a very good plan to have fitted, in connection with it, a tarpaulin apron, to cover the “leadsman” from the feet to the waist. This keeps him dry and adds much to his comfort.
On going into the chains for the purpose of sounding, the leadsman should see the breast-rope properly secured; his line clear, and the end made fast. If at night, he should take the distance from the breast-rope to the water’s edge; then at each cast deduct this distance from the mark at hand and give it as the true sounding.
The Coasting Lead is used in depths from 25 to 100 fathoms, the lead weighing from 25 to 50 pounds.
The Deep-sea Lead is used in depths of over 100 fathoms, and weighs from 80 to 150 pounds.
Both coasting and deep-sea (pronounced “dipsey”) leads are hollowed out at the base to receive anarming of tallow. When the lead strikes, the tallow becomes coated with sand, pebbles, shells or other substances which show the character of the bottom. This information, compared with the description of the sea bottom given on the chart, may prove of value in determining the ship’s position. Instead of being hollowed out at the bottom, the deep-sea lead may have a specimen cup, of brass, at the end, as shown in Fig. 4. The coasting and deep-sea lines are marked alike as follows:
10 fathoms, one knot.
To Sound with the Deep-sea Lead. The men are ranged outside the vessel from the weather mizzen chains to the cathead. The line is passed forward outside and clear of everything. The lead is sent forward on deck, and the line bent to it by the captain of the forecastle. The line is then hauled forward, each man collecting a coil of several fathoms in his hand, commencing forward, until the officer thinks there is line enough out. It is then snatched in a small snatch-block, Fig. 5, secured to the
|after mizzen rigging, or to the weather spanker yang, the remaining part of it being coiled down in a tub or rack, or wound on a reel, clear for running. Everything being in readiness, and the vessel’s headway sufficiently deadened, the officer orders, Stand by! Heave! The captain of the forecastle heaves the lead as far forward as he can, and at the same time cries, Watch-ho! Watch! And each man, as the line runs out from his hand, holds it clear of the side, and repeats the cry, Watch-ho! Watch! In the mean while, the line runs out until the lead touches the bottom, or until a sufficient quantity has been run out to satisfy the officer that no bottom has been found. The men then lay aft and man the line! and walk forward with it; a petty officer being stationed by it, to note the depth of water by the first mark that comes in.If bottom has been found, it will instantly be known by the line bringing up suddenly in running out, or by the arming on the lead after it is hauled up; by which the nature of the bottom is known.To get sounding by the deep-sea lead while lying to in a gale, or in any case when the vessel drifts much to leeward, it is proper to pass the line from to windward around the stern, and then forward on the lee side, and to heave the lead from to leeward, which will bring the line nearly perpendicular by the time the lead touches the bottom.
In heaving the deep-sea lead, the men stationed in the chains should be cautioned not to let the line go until they feel the lead take it, for if the ship is in much shoaler water than was anticipated, it is thus detected at once.
Besides the common lead, there are a variety of “patents” for sounding; the one known as Massey’s lead, being about the most successful. In this, a machine is attached to the lead, and a fan set in motion by its descent. The motion is communicated to a register wheel, and the number of fathoms corresponding to the depth of water is pointed out by an indicator. This lead should also have a good arming of tallow to bring up specimens of the bottom.
The Drift Lead. While at single anchor, it is proper always to have a lead somewhat heavier than the hand-lead, say from fourteen to twenty pounds, over the side, and resting on the bottom, with a man to attend it. Of course, this is only necessary in a stiff breeze, or at night. But in a vessel-of-war, it should be observed as a standing rule, without regard to the weather. By this you will have instant notice if the vessel parts her cable or drags her anchor.
Various methods have been proposed for measuring the rate at which a ship sails; but that most in use is by the Log and Glass.
The Log is a flat piece of thin board, of a sectoral or quandrantal form, Figs. 6a and b, Plate 5, loaded, on the circular side, with lead sufficient to make it swim upright in the water. To this is fastened a line, about 150 fathoms long, called the log-line, which is divided into certain spaces called knots, and is wound on a reel, Fig. 7, which turns very easily. The Glass is of the same form as an Hour-Glass, Fig. 8, and containing such a quantity of sand as will run through the hole in its neck in twenty-eight seconds.
Marking the Log-Line. Previous to marking a new Log-line, it is soaked in water for a few days, in order to get it in the condition it will be when in use. From fifteen to twenty fathoms is allowed for “stray-line;” and then the length of a knot determined (for the 28-second glass) by the following proportion, viz.: As the number of seconds in an hour is to the number of feet in a sea mile, so is the length of the glass to the length of a knot, or,
therefore the length of the knot is 47 feet 4 inches for the 28-second glass.
The velocity of the ship is estimated in knots and tenths of a knot.
The limit of “stray-line” is marked by a piece of red bunting about six inches long, and each length of 47 feet 4 inches after that by a piece of fish-line with one, two, three, etc., knots in it, according to, its number from the “stray-line.”
Each length of 47 feet 4 inches (the “knot”) is subdivided into five equal parts, and a small piece of white bunting about two inches long is turned into the line at every two-tenth division thus formed.
Always, before leaving port, the Navigator has the line thoroughly soaked for a few days, and then all the marks placed at their proper distances. He also compares all the sand-glasses with a watch, and if any should be incorrect, he makes them run the proper time by taking out or putting in sand, as the case requires. During daylight, especially in very damp weather, it is preferable to use a watch to a sand-glass for noting the time. Errors of the glass due to moisture are commonly corrected by drying it at the galley.
Heaving the Log.-To find the ship’s speed is
|called heaving the log, and is thus performed: One man holds the reel, and another the glass; an officer of the watch throws the log over the ship’s stern, on the lee side, and when he observes the stray line is run off (allowed to carry the log out of the eddy of the ship’s wake), and the red rag is gone off, he cries, Turn; the glass-holder answers, Turn; and watching the glass, the moment it is run out, says, Up. The reel being immediately stopped, the last mark run off shows the number of knots, and the distance of that mark from the rail is estimated in tenths. Then the knots and tenths together show the distance the ship has run the preceding hour, if the wind has been constant. But if the wind has not been the same during the whole hour, or interval of time between heaving the log, or if there has been more sail set or handed, a proper allowance must be made. Sometimes, when the ship is before the wind, and a great sea setting after her, it will bring home the log. In such cases, it is customary to allow one mile in ten, and less in proportion if the sea be not so great. Allowance ought also to be made, if there be a head sea.This practice of measuring a ship’s rate of sailing, is founded upon the following principle, that the length of each knot is the same part of a. sea mile;* as twenty-eight seconds is of an hour.In heaving the log, you must be careful to veer out the line as fast as the chip will take it; for if it be left to turn the reel itself, it will come home and deceive you in your reckoning. You must also be careful to measure the log-line pretty often, lest it stretch and deceive you in the distance. Like regard must be had that the glass be just 28 seconds; otherwise no accurate account of the ship’s way can be kept. The glass is much influenced by the weather, running slower in damp weather than in dry. The glass may be examined by a watch, as above stated, or by the following method:-Fasten a plummet on a line, and hang it on a nail, observing that the distance between the nail and middle of the plummet be 39 1/8 inches; then swing the plummet, and notice how often it swings while the glass is running out, and that will be the number of seconds measured by the glass.
If the vessel’s speed is greater than four knots the fourteen-second glass is used instead of the twenty-eight second, and the number of knots run out is doubled to ascertain the actual rate of sailing, as the line is graduated for the twenty-eight second glass. The twenty-eight and fourteen second glasses are called respectively the long and short glasses.
* A statute mile is 5,280 feet. To convert sea miles into statute miles, multiply the former by 1.153. To convert statute miles into sea miles, multiply by the decimal .868.
|The Patent Log is now in constant use, especially on board steamers. It should be rigged out by a spar, so as to clear the wake, and care taken to haul it in whenever the ship is stopped.Massey’s Patent Log is composed of a brass wedge-shaped box, having within three cogged wheels, acting on each other in such proportion that a total revolution of one completes a division of the next (or one-twentieth), a revolution of the next, one-eighth, registering thus from one hundred and sixty miles to tenths, and decimal parts; the action is by the rotation of a spindle with four spirally-fixed wings (termed the rotation, or fly), which turns an endless screw in the box, acting directly on the decimal wheel. It is towed astern by a stout lead line of sixty fathoms, and is registered every time the course is changed, angles taken, &c., but should not be reset until the twenty-four hours have elapsed, or the ship anchors, or goes less than three knots-when it becomes uncertain from not towing horizontally.When great accuracy is required it is well to use two logs, putting one overboard as the other is hauled up, as when the course is changed, etc.
The Taffrail Log, Fig. 9. This is a mechanical log of the same character as Massey’s, but it has the advantage of towing only the fly, the registering apparatus being at the inboard end of the trailing line so that it can be easily read without hauling in the line. In one patent of this kind there is placed between the register and fly a conical hollow metal piece upon which the vibrations due to pitching are taken.
Registering logs are frequently made to strike a bell at every mile or five miles of the run.
Among the various speed indicators which, like the common log, are useful in showing changes of speed, the instrument invented by Ensign Hogg, U. S. Navy, has given very satisfactory results, and may be described as follows:
Fig. 10 shows a sailing vessel with the vacuum instrument represented in Fig. 11, towed astern by a hollow gum tube, the length of which for the largest vessels is 75 feet. The tube is supported in the water at low speeds by the buoy in Fig. 12. The mercurial gauge, Fig. 13, is on board the vessel; at present a metallic gauge is generally substituted.
The action of the speed indicator is as follows: The water rushing through the instrument at A, Fig. 11, causes a vacuum at the small end of the mouth-piece B. This vacuum communicates by means of the gum-tube with the vacuum-gauge on deck, and the greater the vacuum, the greater the speed. The graduations on the vacuum-gauge are found by experiment.
|The only difference with a steamer is that the rubber tube is rigged out about three feet by an outrigger from the ship’s side, and the vacuum instrument is towed alongside.The Ground Log is the common log line with a hand-lead attached, and is used in tideways and currents, in soundings, to ascertain the vessel’s speed over the ground.|