the stern-post above, and the aftmost floor-timbers below, it is
necessary to distinguish them by particular names. Thus the highest is
called the wing-transom: the next, the deck-transom; and afterwards
follow the first, second, and third transoms; together with the
intermediate ones, as represented in fig. 1. plate X. and described in
the explanation thereof.
The vertical direction of the arms or angles of the transoms, with
regard to the ship’s length, are expressed in the plane of ELEVATION;
and their horizontal curves are also delineated on the plane of
Projection; both of which are represented under those terms in plate I.
and described in the general explanation of the planes in the article
_Naval_ ARCHITECTURE.
The highest transoms are connected to the ship’s quarter by knees, which
are bolted to those pieces, and to the after-timbers. See the article
SLEEPERS.
TRANSPORT. See the article SHIP.
TRANSPORTING, the act of removing a ship from one place to another, by
the help of anchors and ropes. See WARPING.
TRAVELLER, _racambeau_, a sort of _thimble_, whose diameter is much
longer, in proportion to the breadth of its surface, than the common
ones, fig. 3. plate XII. It is furnished with a tail formed of a piece
of rope, about three feet in length, one end of which encircles the
ring, to which it is _spliced_. These machines are principally intended
to facilitate the _hoisting_ or _lowering_ of the top-gallant-yards at
sea: for which purpose two of them are fixed on each _back-stay_,
whereon they slide upwards and downwards, like the ring of a curtain
upon its rod: being thus attached to the extremities of the
top-gallant-yard, they prevent it from swinging backwards and forwards,
by the agitation of the ship, whilst the yard is hoisting or lowering at
sea.
TRAVERSE, in navigation, implies a compound course, or an assemblage of
various courses, lying at different angles with the meridian. Thus fig.
2. plate XI. exhibits the traverses formed by a ship, when making an
oblique progression against the direction of the wind, as explained in
the article TACKING.
The true course and distance resulting from this diversity of courses is
discovered by collecting the difference of latitude and departure of
each course, and reducing the whole into one departure and one
difference of latitude, according to the known rules of trigonometry.
This reduction will immediately ascertain the base and perpendicular;
or, in other words, will give the difference of latitude and departure
to discover the course and distance. See NAVIGATION.
TRAVERSE-BOARD, a thin circular piece of board, marked with all the
points of the compass, and having eight holes bored in each, and eight
small pegs hanging from the center of the board. It is used to determine
the different courses run by a ship during the period of the watch; and
to ascertain the distance of each course. This implement is particularly
useful in light and variable winds, at which time the helmsman marks the
course every half hour, by fixing a peg in that point of the compass
whereon the ship had advanced. Thus, if the wind is northerly at the
beginning of the watch, the ship, being _close-hauled_ on the larboard
_tack_, will steer W. N. W. If, after the first half hour, the wind
changes to N. _by_ W. the ship will fall off to W. _by_ N. both of these
courses are marked by the helmsman upon the traverse-board, by putting
in one peg for every half hour on which she steers the same course; as,
one peg into W. N. W. and two pegs into W. _by_ N. if she sails an hour
on the latter course; and so on. The lee-way and variation of the
compass are afterwards allowed by the pilot, on summing up the whole.
TREE-NAILS, _gournables_, certain long cylindrical wooden pins, employed
to connect the planks of a ship’s side and bottom to the corresponding
timbers.
The tree-nails are justly esteemed superior to spike-nails or bolts,
which are liable to rust, and loosen, as well as to rot the timber; but
it is necessary that the oak of which they are formed should be solid,
close, and replete with gum, to prevent them from breaking and rotting
in the ship’s frame. They ought also to be well dried, so as to fill
their holes when they are swelled with moisture. They have usually one
inch in thickness to 100 feet in the vessel’s length; so that the
tree-nails of a ship of 100 feet long, are one inch in diameter; and one
inch and a half for a ship of 150 feet.
TRESTLE-TREES, _tesseaux_, two strong bars of timber fixed horizontally
on the opposite sides of the lower mast-head, to support the frame of
the top, and the weight of the top-mast. See MAST and TOP.
TRIM, _manege du navire_, (_trimman_, Sax. _to build_) implies, in
general, the state or disposition by which a ship is best calculated for
the several purposes of navigation.
Thus the trim of the _hold_ denotes the most convenient and proper
arrangement of the various materials contained therein, relatively to
the ships motion or stability at sea. The trim of the masts and sails is
also their most apposite situation, with regard to the construction of
the ship, and the effort of the wind upon her sails.
As the _stowage_ of the hold, or the disposition of the several articles
of the cargo, considerably affects the ship’s motion and stability, it
will be necessary to give a general idea of the action of a heavy body
upon the fluid that supports it, and the re-action of the fluid on the
floating body.
The whole weight of any body, then, may be considered as united in its
center of gravity; so that, if it were suspended by a line fastened to
this center, the line would hang in a perpendicular position, as
directed through the center of gravity to the center of the earth. A
body which floats in a fluid is not, however, supported by its center of
gravity, but by the compression of the surrounding filaments of water:
and each of these, being considered as infinitely small, will act upon a
very minute portion of the surface of the floating body, with regard to
the specific gravity, and conform to a principle applicable to all
fluids, in proportion to the height of these filaments, viz. That the
weight of a column of any fluid will be in proportion to the specific
gravity of the fluid and the height of the column multiplied by its
base.
But as heavy bodies endeavour, by their gravity, to approach the center
of the earth, in a vertical line passing through their centers; so the
pressure of fluids endeavours to carry bodies in a vertical, tending
from the center of the earth towards their surface, and passing through
the center of gravity of the submerged part, which forces them towards
the surface. So, in any submerged body at rest, these two opposite
forces coincide in the same vertical, acting in a direction quite
contrary to each other. _Bouguer’s Traité du navire._
From this theory it results, that the stability or trim of a ship
chiefly depends upon her construction, as considering the bottom to be
homogeneous. This, however, can only happen when her cargo consists of
the same materials throughout, as with corn, salt, or any species stowed
in bulk, and when her hold is entirely filled. For if the ship has not
sufficient breadth to resist the effort of the wind upon her sails; or
if she is built too high, or too sharp in the floor, her center of
gravity will be too high, and she will be very _crank_, i. e. apt to
overturn.
But as the _stiffness_ of a ship, or quality to carry sail without
danger of overturning, depends very much on the _stowage_ of the hold,
the center of gravity may thereby be considerably lowered, by which her
stability will be increased in proportion. It is a general maxim amongst
mariners, that a ship will not carry sufficient sail till she is laden
so deep that the surface of the water may glance on her extreme breadth
_amidships_. She must therefore have a great deal of weight, as ballast,
&c. to bring her to this situation, which is called a good sailing trim.
Several circumstances are also to be particularly considered with regard
to the quality, weight, and stowage of the ballast. The center of
gravity being placed too high, will render the ship incapable of
carrying a sufficient quantity of sail; and by having it too low, she
will be in danger of rolling away her masts. When it is placed too far
forward, the ship will _pitch_, and _labour_ heavily; and when too far
aft, she will occasionally be exposed to the dangerous circumstance of a
_pooping_ sea. These extremes being carefully avoided, it remains to
proportion the contents of every part of the _hold_ to its capacity, and
to place the lightest materials uppermost. See STOWAGE.
TRIM, when applied to the sails, denotes the general arrangement which
is best calculated to accelerate the ship’s course, according to the
direction of the wind. See the article SAILING.
If the ship were always to sail before the wind, it would be a very
simple operation to trim the sails; because nothing else could be
required than to dispose them so as to receive the greatest possible
effort of the wind, which is evidently performed by arranging them at
right angles with its direction. But, when the current of wind acts more
directly upon the ship’s side, it necessarily falls more obliquely on
the surface of the sails, so as to diminish their effort to push the
ship forward; and to augment their tendency to make her incline to one
side. Hence we may conclude, that an increase of the wind, when
accompanied with a variation unfavourable to the ship’s course, will by
no means augment her velocity; because the force previously employed to
push her forward, will afterwards operate to overturn her; and because
this impression renders it necessary to reduce the quantity of sail; the
effort of which is farther diminished by the obliquity of the action of
the wind upon its surface.
By this theory it appears, that the effect of the wind to advance the
ship decreases in proportion to its obliquity with any sail upon which
it operates.
The mechanical disposition of the sails, according to every direction of
the wind upon their surfaces, is copiously described in the articles
CLOSE-HAULED, LARGE, SAILING, and TACKING.
TRIM, when expressed of the masts, denotes their position with regard to
the ship and to each other. Thus, in the latter sense, they should
neither be too near nor too far apart; and, in the former, they should
not be too far forward or aft; and, according to the situation or
quality which communicates a greater velocity to the vessel, they should
either be upright, or inclining aft, or forward.
TRIM _the boat_. See BOAT, and the phrases succeeding it.
_Sharp_-TRIMMED, the situation of a ship’s sails in a scant wind.
TRIMONEER, a barbarous corruption of TIMONEER. See that article.
TRIP, a cant phrase, implying an outward-bound voyage, particularly in
the coasting navigation. It also denotes a single _board_ in _plying_ to
windward.
TRIPPING, the movement by which an anchor is loosened from the bottom by
its cable or buoy-ropes. See ATRIP.
TROUGH, a name given to the hollow, or interval between two high waves,
which resembles a broad and deep trench perpetually fluctuating. As the
_setting_ of the sea is always produced by the wind, it is evident that
the waves, and consequently the trough or hollow space between them,
will be at right angles with the direction of the wind. Hence a ship
rolls heaviest when she lies in the trough of the sea.
TROWSERS, a sort of loose breeches of canvas worn by common sailors.
TRUCK, a piece of wood, which is either conical, cylindrical, spherical,
or spheroidical.
Thus the trucks fixed on the spindle of a mast-head, and which are
otherwise called _acorns_, are in the form of a cone: and those which
are employed as wheels to the gun-carriages are cylinders. The trucks of
the parrels assume the figure of a globe; and, lastly, those of the
flag-staffs resemble an oblate spheroid. See the articles ACORN, CANNON,
PARREL, and FLAG-STAFF.
Trucks of the shrouds are nearly similar to those of the parrels: they
are fastened to the shrouds about twelve or fourteen feet above the
deck, the hole in the middle being placed perpendicularly to contain
some rope which passes through it. The intention of these is to guide
the sailors to the particular rope, which might otherwise be easily
mistaken for some other of the same size, especially in the night.
_Speaking_-TRUMPET, _trompette marine_, a trumpet of brass or tin used
at sea, to propagate the voice to a great distance, or to convey the
orders from one part of the ship to another, in tempestuous weather, &c.
when they cannot otherwise be distinctly heard by the persons to whom
they are directed.
_Fire_-TRUNK. See the article FIRE-SHIP.
TRUNNIONS, _tourillons_, the two knobs or arms which project from the
opposite sides of a piece of artillery, and serve to support it in the
carriage. See CANNON and MORTAR.
TRUSS, (_trousse_, Fr.) a machine employed to pull a yard home to its
respective mast, and retain it firmly in that position.
As the truss is generally used instead of a parrel, it is rarely
employed, except in flying top-gallant-sails, which are never furnished
with parrels. It is no other than a ring or traveller, which encircles
the mast, and has a rope fastened to its after-part, leading downward to
the top or decks; by means of which the truss may be straitened or
slackened at pleasure. The _haliards_ of the top-gallant-sail being
passed through this ring; and the sail being hoisted up to its utmost
extent; it is evident, that the yard will be drawn close to the mast, by
pulling down the truss close to the upper part of the sail. For, without
the truss, the sail and its yard would be blown from the mast, so as to
swing about, by the action of the wind, and the rocking of the vessel;
unless the yard were hoisted close up to the pulley wherein the haliards
run; which seldom is the case in flying top-gallant-sails, because they
are usually much shallower than those which are fixed or _standing_.
TRUSS-PARREL. See PARREL.
TRYING, _à la cape_, the situation in which a ship lies nearly in the
_trough_ or hollow of the sea in a tempest, particularly when it blows
contrary to her course.
In _trying_, as well as in _scudding_, the sails are always reduced in
proportion to the increase of the storm. Thus, in the former state, a
ship may lie by the wind under a whole main-sail, a whole fore-sail, or
a whole mizen; or under any of those sails, when diminished by the
_reef_ or _balance_. As the least possible quantity of sail used in
scudding are the _goose-wings_ of the foresail; so in _trying_, the
smallest portion is generally the mizen-staysail or main-staysail: and
in either state, if the storm is excessive, she may lie with all the
sails furled, or, according to the sea-phrase, _under bare poles_.
The intent of spreading a sail at this time is to keep the ship more
steddy, and, by pressing her side down in the water, to prevent her from
rolling violently; and also to turn her _bow_ towards the direction of
the wind, so that the shock of the waves may fall more obliquely on her
flank, than when she lies along the trough of the sea. While she remains
in this situation, the helm is fastened close to the lee-side, or, in
the sea-language, _hard a-lee_, to prevent her as much as possible from
falling-off. But as the ship is not then kept in equilibrio by the
effort of her sails, which at other times counterbalance each other at
the _head_ and _stern_, she is moved by a slow but continual vibration,
which turns her head alternately to windward and to leeward, forming an
angle of three or four points in the interval. That part where she
stops, in approaching the direction of the wind, is called her
_coming-to_, and the contrary excess of the angle _to leeward_ is termed
her _falling-off_.
Thus, suppose the wind northerly, and a ship trying with her starboard
side to windward: if, in turning her head towards the source of the
wind, she arrives at N. W. ½ N. or N. 39° W. and then declines to the
leeward as far W. ½ S. or S. 84° W, the former will be called her
coming-to, and the latter her falling-off. In this position she advances
very little according to the line of her length, but is driven
considerably to leeward, as described in the articles DRIFT and LEE-WAY.
TUCK, a name given to that part of the ship where the ends of the
bottom-planks are collected together immediately under the stern or
counter.
When this part, instead of being incurvated, and forming a convex
surface, assumes the shape of a vertical or oblique plane, it is said to
be square, as represented in fig. 8. plate IX. A square tuck is
accordingly terminated above by the wing-_transom_, and below and on
each side by the _fashion-pieces_.
TUMBLING-HOME, _encabanement_, that part of a ship’s side which falls
inward above the extreme breadth, so as to make the ship gradually
narrower from the lower deck upwards. This angle is represented in
general throughout all the timbers in the plane of _projection_, plate
I. It is also more particularly expressed by Q T in the MIDSHIP-FRAME,
plate VII. where it is evident, that the ship grows narrower from Q
towards T. N. B. In all our old sea-books, this narrowing of a ship from
the extreme breadth upwards is called housing-in. See UPPER-WORK.
TURNING-_to-windward_, _chicaner le vent_, that operation in sailing
wherein a ship endeavours to make a progress against the direction of
the wind, by a compound course, inclined to the place of her
destination. This method of navigation is otherwise called _plying_. See
also BEATING and TACKING.
TYE, _itague_, a sort of _runner_ or thick rope, used to transmit the
effort of a tackle to any _yard_ or _gaff_, which extends the upper part
of a sail.
The tye is either passed through a block fixed to the mast-head, and
afterwards through another block moveable upon the yard or gaff intended
to be hoisted; or the end of it is simply fastened to the said yard or
gaff, after communicating with the block at the mast-head. See also the
article JEARS.
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.