V.
VAN, avante-garde, the foremost division of any naval armament, or that part which usually leads the way to battle; or advances first in the order of sailing. See Center, Fleet, and Rear.
VANE, a thin slip of bunting hung to the mast-head, or some other conspicuous place in the ship, to show the direction of the wind. See b, fig. 1. plate [I]. It is commonly sewed upon a wooden frame called the stock, which contains two holes whereby to slip over the spindle, upon which it turns about as the wind changes.
Dog-Vane, panon, a small light vane, formed of a piece of packthread about two feet in length, upon which are fixed five or six thin slices of cork stuck full of light feathers. It is usually fastened to the top of a staff two yards high, which is placed on the top of the ship’s side on the quarter-deck, in order to shew the direction of the wind to the helmsman, particularly in a dark night, or when the wind is extremely feeble.
VANGS, a sort of braces to support the mizen gaff, and keep it steddy. They are fixed on the outer-end or peek, and reach downwards to the aftmost part of the ship’s side, where they are hooked and drawn tight, so as to be slackened when the wind is fair; and drawn in to windward when it becomes unfavourable to the ship’s course.
VARIATION, the angle contained between the true meridian and the magnetic meridian.
‘After the discovery of that most useful property of the magnet, or loadstone, namely, the giving hardened iron and steel a polarity, the compass was for many years used without knowing that its direction in any wise deviated from the poles of the world: and about the middle of the 16th century, so certain were some of its inflexibly pointing to the north, that they treated with contempt the notion of the variation, which about that time began to be suspected[[55]]. However, careful observations soon discovered, that in England, and its neighbourhood, the needle pointed to the eastward of the true north: but the quantity of this deviation being known, mariners became as well satisfied as if the compass had none; because they imagined that the true course could be obtained by making allowance for the true variation.
‘From successive observations made afterwards, it was found, that the deviation of the needle from the north was not a constant quantity; but that it gradually diminished, and at last, about the year 1660, it was found at London that the needle pointed due north, and has ever since been getting to the westward, and now the variation is more than 20 degrees to the westward of the north: so that in any one place it may be suspected the variation has a kind of libratory motion, traversing through the north to unknown limits eastward and westward. But the settling of this point must be left to time.
‘During the time of the said observations it was also discovered, that the variation of the needle was different in different parts of the world, it being west in some places when it was east in others; and in places where the variation was of the same name, yet the quantity of it greatly differed. It was therefore found necessary, that mariners should every day, or as often as they had opportunity, make, during their voyage, proper observations for an amplitude or azimuth; whereby they might be enabled to find the variation of the compass in their present place, and thence correct their courses.’ Robertson’s Elements of navigation.
Dr. Halley published, in the last century, a theory of the variations of the compass. In this work he supposes there are four magnetic poles in the earth, two of which are fixed and two moveable, by which he explains the different variation of the compass, at different times, in the same place. But it is impossible to apply exact calculations to so complicated an hypothesis. M. Euler, son of the celebrated geometrician of that name, has however shewn, that two magnetic poles placed on the surface of the earth will sufficiently account for the singular figure assumed by the lines which pass through all the points of equal variation in the chart of Dr. Halley.
M. Euler first examines the case, wherein the two magnetic poles are diametrically opposite; 2d. he places them in the two opposite meridians, but at unequal distances from the poles of the world; 3d. he places them in the same meridian. Finally, he considers them situated in two different meridians. These four cases may become equally important; because, if it is determined that there are only two magnetic poles, and that these poles change their situations, it may some time hereafter be discovered that they pass through all the different positions.
Since the needle of the compass ought always to be in the plane which passes through the place of observation and the two magnetic poles, the problem is reduced to the discovery of the angle contained between this plane and the plane of the meridian. M. Euler, after having examined the different cases, finds, that they also express the earth’s magnetism, represented in the chart published by Mess. Mountaine and Dodson in 1744, particularly throughout Europe and North America, if the following principles are established.
Between the Arctic pole and the magnetic pole 14° 53´.
Between the Antarctic pole and the other magnetic pole 29° 23´.
53° 18´ The angle at the north pole, formed by the meridians passing through the two magnetic poles.
250° The longitude of the meridian, which passes over the northern magnetic pole.
As the observations which have been collected with regard to the variation are, for the most part, loose and inaccurate, it is impossible to represent them all with precision; and the great variations observed in the Indian ocean, seem to require, says M. Euler, that the three first quantities should be 14, 35, and 63 degrees. In the mean time, the general agreement is sufficiently satisfactory.
The high reputation of Dr. Halley’s magnetical chart renders it more particularly necessary to point out the errors contained therein[[56]]. There is evidently too little distance between the lines of no variation, of which one crosses the equator 17° westward of London, and the other 119° to the eastward. This makes 136 degrees only; whereas it should necessarily exceed 180 and even 200, inasmuch as the pole of the world is supposed farther distant from the magnetic pole towards the south than in the north, as is required by the other phænomena. Again, upon the coasts discovered by Diemen, there was no variation in 1642; and Dr. Halley also supposes there was none in 1700. Meanwhile, by the alteration observed at Paris, the line of no variation should be advanced 60° towards the south, which will agree better with the calculations, and prove that the distance of the two intersections was really greater than Dr. Halley had established.
The table of variation of Mess. Mountaine and Dodson is accompanied with several interesting particulars, which equally deserve to be inserted here.
At Barbadoes, (says Capt. Snow) the variation seems very nearly at a stand; for in the road I observed 5° east; and by Dr. Halley’s draught, in the year 1701, 5½ degrees. In 1747, at Port Royal keys, Jamaica, I observed the variation 7° 20´ E.; and on the coast of Carthagena, the same week, off the high land of Santa Martha, 7° 45´ nearly south of Port Royal. Therefore these curves are not much altered: the curve at Jamaica is nearly at a stand, as though tied, and the south part of them with the rest dropping to the westward.
Under the equator, in longitude 40° E. from London, the highest variation during the whole fifty-six years appears to be 17°¼ W. and the least 16°½ W.: and in latitude 15° N. longitude 60° W. from London, the variation has been constantly 5° E.: but in other places the case has been widely different. For in the latitude of 10° S. longitude 60° E. from London, the variation has decreased from 17° W. to 7°¼ W.; and in latitude 10° S. longitude 5° W. from London, from 2°¼ W. to 12°¾ W.; and in latitude 15° N. longitude 20°, it has increased from 1° W. to 9° W.
But there is still a more extraordinary appearance in the Indian seas. For instance, under the equator:
| LONGITUDE | MAGNETICAL VARIATION | |||
|---|---|---|---|---|
| East from London. | in 1700. | in 1756. | ||
| Degrees. | Degrees. | Degrees. | ||
| 40 | 16¾ | West. | 16¼ | West. |
| 45 | 17¾ | W. | 14½ | W. |
| 50 | 17½ | W. | 11¾ | W. |
| 55 | 16½ | W. | 8¾ | W. |
| 60 | 15¼ | W. | 6 | W. |
| 65 | 13½ | W. | 4½ | W. |
| 70 | 11½ | W. | 3¼ | W. |
| 75 | 9¾ | W. | 1 | W. |
| 80 | 7¾ | W. | 0¼ | East. |
| 85 | 5½ | W. | 1¼ | E. |
| 90 | 4¼ | W. | 1 | E. |
| 95 | 3¼ | W. | 0½ | West. |
| 100 | 2½ | W. | 1 | W. |
Where the west variation, in the longitude 40° E. is the same in both the above years; and in 1700 the west variation seemed to be regularly decreasing from longitude 50° E. to the longitude 100° E.; but in 1756, we find the west variation decreasing so fast, that we have east variation in the longitude 80°, 85°, and 90° E.; and yet in the longitude 95° and 100° E. we have west variation again. Philosophical Transactions for the year 1757.
To these remarks may be subjoined the following extracts from the Exposition du calcul astronomique, by M. de la Lande.
At the royal observatory in Paris, a magnetical needle of four inches deviated from the N. 18° 10´ towards the west, on the 15th of February 1759: and on the 22d of April 1760, the same needle varied 18° 20´. It is indeed natural to conceive, that nothing can be precisely ascertained by ten minutes upon a circle whose diameter is only four inches. It is nevertheless sufficiently evident, that this variation continues to increase at Paris. In 1610 the needle declined 8° towards the east, so that the variation has changed 26° 20´ in the space of 150 years; and this appears particularly since 1740: for the same needle, which has always been used by M. Maraldi, is more than 3° advanced towards the west, beyond what it was at that period; and this makes 9´ in one year.
To VEER and haul, to pull a rope tight, by drawing it in and slackening it alternately, till the body to which it is applied acquires an additional motion, like the increased vibrations of a pendulum, so that the rope is straitened to a greater tension with more facility and dispatch. This method is particularly used in hauling the bowlines.
The wind is said to veer and haul when it alters its direction, and becomes more or less fair. Thus it is said to veer aft and to haul forward.
To Veer away the cable. See Cable.
VEERING, virer vent arriere, the operation by which a ship, in changing her course from one board to the other, turns her stern to windward. Hence it is used in opposition to tacking, wherein the head is turned to the wind, and the stern to leeward.
Thus the ship A, fig. 8. plate [XI]. having made the necessary dispositions to veer, bears away gradually before the wind, till it blows obliquely upon the opposite side, which was formerly to leeward, as at a; and as the stern necessarily yields to this impression of the wind, assisted by the force of the helm, and the action of the waves upon the same quarter, the side which was formerly to leeward soon becomes to windward, as in the point a.
Since, by this movement, a ship loses ground considerably more than by tacking, it is rarely practised except in cases of necessity or delay: as, when the violence of the wind and sea renders tacking impracticable; or when her course is slackened to wait for a pilot, or some other ship in company, &c.
It has been observed in the article Tacking, that the change of motion in any body, will be in proportion to the moving force impressed, and made according to the right line in which that force operates. Hence it is evident, that veering as well as tacking is a necessary consequence of the same invariable principle; for as, in the latter, almost the whole force of the wind and of the helm are exerted on the hind part of the ship, to turn the prow to windward; so, in the former, the same impression, assisted by the efforts of the helm, falls upon the prow, to push it to leeward; and the motion communicated to the ship must in both cases necessarily conspire with the action of the wind.
Thus, when it becomes necessary to veer the ship, the sails towards the stern are either furled, or brailed up, and made to shiver in the wind; whilst those near the head are spread abroad, so as to collect the whole current of air which their surfaces can contain. Hence, while the whole force of the wind is exerted on the fore part of the ship to turn her about, its effect is considerably diminished, or altogether destroyed, on the surfaces of the after-sails. The fore part accordingly yields to the above impulse, and is put in motion; and this movement, conspiring with that of the wind, pushes the ship about as much as is necessary to produce the effect required. When she is turned so that the wind will act upon that quarter which was formerly to leeward, as at the point a, fig. 8. her circular motion will be accelerated by extending some of the sails near the stern, as the mizen, and by placing those at the prow more obliquely, which will wheel the vessel round with her bow to the windward; in the same situation, with regard to the wind, as when close-hauled, or tacking.
When the tempest is so violent as to prevent the use of sails, the effort of the wind operates almost equally on the opposite ends of the ship, so that the masts and yards situated at the head and stern counterbalance each other. The effect of the helm is also considerably diminished, because the head-way, which gives life and vigour to all its operations, is at this time feeble and ineffectual. Hence it is necessary to defray this equilibrium which subsists between the masts and yards afore and abaft, and to throw the balance forward, in order to prepare for veering. This is accordingly performed by bracing the foremost yards across the direction of the wind, and arranging those on the main-mast and mizen mast directly in the line of the wind. If this expedient proves unsuccessful, and it is absolutely necessary to veer, in order to save the ship from destruction, by oversetting or running ashore, the mizen-mast must instantly be cut away, and even the main-mast, if she yet remains incapable of answering the helm by bearing away before the wind.
VENT. See the articles Cannon and Windage.
VESSEL, batiment, a general name given to the different sorts of ships which are navigated on the ocean, or in canals and rivers. It is, however, more particularly applied to those of the smaller kind, furnished with one or two masts.
It has already been remarked in the article Ship, that the views of utility, which ought always to be considered in a work of this kind, seemed to limit our general account of shipping to those which are most frequently employed in European navigation. We have therefore collected into one point of view the principal of these in plate [XII].; so that the reader who is unacquainted with marine affairs, may the more easily perceive their distinguishing characters, which are also more particularly described under the reflective articles.
Thus fig. 4. plate [XII]. exhibits a snow under sail; fig. 5. represents a ketch at anchor; fig. 6. a brig or brigantine; fig. 7. a bilander; fig. 8. a xebec; fig. 9. a schooner; fig. 10. a galliot; fig. 11. a dogger; all of which are under sail; fig. 12. & 13. two galleys, one of which is under sail, and the other rowing; and fig. 14. a sloop.
The ketch, whose sails are furled, is furnished with a try-sail, like the snow; and it has a fore-sail, fore-staysail, and jib, nearly similar to those of a sloop; but the sails on the main-mast and mizen-mast are like those of a ship. The main-sail and main-topsail of the brig are like those of the schooner; and the fore-mast is rigged and equipped with sails in the same manner as the ship and snow. The sails, masts, and yards of the xebec, being extremely different from these, are described at large under the article. In the schooner both the mainsail and foresail are extended by a boom and gaff, as likewise is the sloop’s mainsail; the sails of the dogger and galliot are sufficiently expressed in the plate; and, finally, the galleys are navigated with lateen-sails, which are extremely different from those of the vessels above described.
Agent VICTUALLER. See Agent Victualler.
To UNBALLAST, delester, to discharge the ballast of a ship.
UNBENDING, désamarrer, generally implies the act of taking off the sails from their yards and stays; of casting loose the anchors from their cables, or of untying one rope from another. See also Bend.
UNBITTING, débitter, the operation of removing the turns of a cable from off the bits. See Bits and Cable.
To UNDER-RUN, parcourir, to pass under or examine any part of a cable or other rope, in order to discover whether it is damaged or intangled.
It is usual to under-run the cables in particular harbours, as well to cleanse them with brooms and brushes from any filth, ooze, shells, &c. collected in the stream; as to examine whether they have sustained any injury under the surface of the water; as, from rocky ground, or by the friction against other cables or anchors.
Plate. xii to face Vessel
To Under-run a tackle, is to separate the several parts of which it is composed, and range them in order, from one block to the other; so that the general effort may not be interrupted, when it is put in motion.
Under sail, the state of a ship when she is loosened from her moorings, and under the government of her sails and rudder. See Helm and Sail.
UNLACING, déboutonner, the act of loosening and taking off the bonnet of a sail from its principal part.
To UNMOOR, desafourcher, is to reduce a ship to the state of riding by a single anchor and cable, after she has been moored or fastened by two or more cables. See the articles Anchor and Mooring.
UNREEVING, the act of withdrawing or taking out a rope from any channel through which it had formerly passed; as in a block, thimble, dead-eye, &c. See Reeve.
To UNRIG a ship, défuner, is to deprive her of the standing and running rigging.
VOYAL, tournevire, a large rope used to unmoor, or heave up the anchors of a ship, by transmitting the effort of the capstern to the cables.
This is performed by fastening one part of the voyal to the cable in several places, and by winding another part thereof three or four times about the capstern, which answers the same purpose as if the cable itself were in that manner wound about the capstern; and the voyal being much lighter and more pliant, is infinitely more convenient in this exercise. See the articles Capstern and Nipper.
If the cable is drawn into the ship by the main capstern, the voyal is used without any block: but if the capstern in the fore-part of the ship be employed for this purpose, the voyal usually passes through a large block attached to the main-mast; and thence communicates with the jear-capstern.
UPPER-DECK, the highest of those decks which are continued throughout the whole of a ship of war, or merchantman, without any interruption, of steps or irregular ascents. See Deck and Waist.
UPPER-WORK, oeuvres mortes, a general name given to all that part of a ship which is above the surface of the water when she is properly balanced for a sea-voyage: hence it may be considered as separated from the bottom by the main wale, as explained particularly in the article Naval Architecture.
UPRIGHT, the situation wherein the opposite sides of a ship are equally elevated above the surface of the water, as in fig. 2. plate [VI].; or when she neither inclines to the right nor left, with regard to the vertical position of her stem and stern-post.
USES AND CUSTOMS of the sea; certain general principles which compose the basis of marine jurisprudence, and regulate the affairs of commerce and navigation.