Encyclopaedia Britannica > Volume 21, ROT-Siam

Fasten¬
ing.
Decks.
Caulk¬
ing.
820
SHIPBUILDING
Of the internal planking the lowest strake, or combination of
strakes, in the hold, is called the limber-strake. A limber is a
passage for water, of which there is one throughout the length of
the ship, on each side of the keelson, in order that any leakage
may find its way to the pumps.
The whole of the plank in the hold is called the ceiling. Those
strakes which come over the heads and heels of the timbers are
worked thicker than the general thickness of the ceiling, and are
distinguished as the thick strakes over the several heads. The
strakes under the ends of the beams of the different decks in a
man-of-war, and down to the ports of the deck below, if there were
any ports, were called the clamps of the particular decks to the
beams of which they are the support—as the gun-deck clamps, the
middle-deck clamps, &c. The strakes which work up to the sills
of the ports of the several decks were called the spirketting of
those decks—-as gun-deck spirketting, upper-deck spirketting, &c.
The. fastening of the plank is either “ single,” by which is meant
one fastening only in each strake as it passes each timber or
frame ; or it may be_ “double,” that is, with two fastenings into
each frame which it crosses ; or, again, the fastenings may be
“double and single,” meaning that the fastenings are double and
single alternately in the frames as they cross them. The fastenings
of planks consist generally either of nails or treenails, excepting
at the butts, which are secured by bolts. Several other bolts
ought to be driven in each shift of plank as additional security.
Bolts which are required to pass through the timbers as securities
to the shelf, waterway, knees, &c., should be taken advantage of
to supply the place of the regular fastening of the plank, not only
for the sake of economy, but also for the sake of avoiding unneces-
sarily wounding the timbers.
ihe decks of a wooden ship must not be considered merely as
platforms, but must be regarded as performing an important part
towards the general strength of the whole fabric. They are
generally laid in a longitudinal direction only, and are then use-
ful as a tie to resist extension, or as a strut to resist compression.
The outer strakes of decks at the sides of the ship are generally of
hard wood, and of greater thickness than the deck itself ; they are
called the waterway planks, and are sometimes dowelled to the
upper, surface of each beam. Their rigidity and strength is of
great impoitance, and great attention should be paid to them, and
caie taken that their scarphs are well secured by through-bolts,
and that there is a proper shift between their scarphs and the
scarphs of the shelf.
When the decks are considered as a tie, the importance of keep¬
ing as many strakes as possible entire for the whole length of the
ship must be evident; and a continuous strake of iron or steel
plates beneath the decks is of great value in this respect. The
straighter the deck, or the less the sheer or upward curvature at
the ends that may be given to it, the less liable will it be to any
alteration of length, and the stronger will it be. The ends of the
different planks forming one strake were made to butt on one beam,
and, as the fastenings are driven close to the ends, they did not
possess much strength to resist being torn out. The shifts of the
butts, therefore, of the different strakes required great attention
because the transference of the longitudinal strength of the deck
from one plank to another was thus made by means of the fasten-
mgs to the beams, the strakes not being united to each other
sideways. The introduction of iron decks or partial decks under
the wood has modified this.
These fastenings have, also to withstand the strain during the
process of caulking, which has a tendency to force the planks
sideways from the seam ; and, as the edges of planks of hard wood
will be less crushed or compressed than those of soft wood when
acted on by the caulking-iron, the strain to open the seam between
them to receive the caulking will be greater than with planks of
softer wood, and will require more secure fastenings to resist it
It may also be remarked that the quantity of fastenings should
inciease with the thickness of the plank which is to be secured
se^ oa^um caulking will have the greater mechani¬
cal effect the thicker the edge.
When the planks are fastened, the seams or the intervals
between the edges of the strakes are filled with oakum, and this is
beaten m or caulked with such care and force that the oakum
while undisturbed, is almost as hard as the plank itself. If the
openings of the seam were of equal widths throughout their depth
between the planks, it would be impossible to make the caulking
sufficiently compact to resist the water. At the bottom edges of
the seams the planks should be in contact throughout their length,
and ii om this contact they should gradually open upwards so
that, at the outer edge of a plank 10 inches thick, the space should
be about xt °f an inch, that is, about xV of an inch open for every
inch of thickness. It will hence be seen that, if the edges of the
planks are so prepared that when laid they fit closely for their
whole thickness, the force required to compress the outer edge by
driving the caulking-iron into the seams, to open them sufficiently
must be very great, and the fastenings of the planks must be such
as to be able to resist it. Bad caulking is very injurious in every
way, as leading to leakage and to the rotting of the planks them¬
selves at their edges.
Ships are generally built on blocks which are laid at a declivity Launch-
of about -g- inch to a foot. This is for the facility of launching ing.
them The inclined plane or sliding plank on which they are
launched has rather more inclination, or about | inch to the foot
for large ships, and a slight increase for smaller vessels. This
inclination will, however, in some measure, depend upon the depth
of water into which the ship is to be launched.
While a ship is in progress of being built her weight is partly
supported by her keel on the blocks and partly by shores In
order to launch her the weight must be taken off these supports
and transferred to a movable base ; and a platform must be erected
for the movable base to slide on. This platform must not only be
laid at the necessary inclination, but must be of sufficient height
to enable the ship to be water-borne and to preserve her from
striking the ground when she arrives at the end of the ways,
lor this purpose an inclined plane a, a (fig. 14), purposely left
unplaned to diminish the adhesion, is laid on each side the keel
and at about one-sixth the breadth of the vessel distant from
it, and firmly secured on blocks fastened in the slipway. This
Fig. 14.
inclined plane is called the sliding-plank. A long timber, called a
bilgeway o, b, with, a smooth under-surface, is laid upon this
plane ; and upon this timber, as a base, a temporary frame-work
of shores c, c, called “ poppets, ” is erected to reach from the bilge¬
way to the ship. The upper part of this frame-work abuts against
a plank d, temporarily fastened to the bottom of the ship, and
firmly cleated by cleats e, e, also temporarily secured to the
bottom When it is all in place, and the sliding-plank and under
side of the bilgeway finally greased with tallow, soft soap, and oil
the whole framing is set close up to the bottom, and down on the
sliding plank, by wedges /, /, called slivers or slices, by which
means the ship s weight is brought upon the “ launch ” or cradle
\\ hen the launch is thus fitted, the ship may be said to have
tliree keels, two of which are temporary, and are secured under her
bilge In consequence of this width of support, all the shores may
be safely taken away. This being done, the blocks on which the
ship was built, excepting a few, according to the size of the ship
under the foremost end of the keel, are gradually taken from under
her as the tide rises, and her weight is then transferred to the two
temporary keels, or the launch, the bottom of which launch is
formed by the bilgeways, resting on the well-greased inclined
planes. Ihe only preventive now to the launching of the ship
is a short shore, called a dog-shore on each side, with its heel
hrmly cleated on the immovable platform or sliding-plank, and its
head abutting against a cleat secured to the bilgeway, or base
of the movable part, of the launch. Consequently, when this shore
is removed, the ship is free to move, and her weight forces her
down the inclined plane to the water. To prevent her ruuniim
out of her straight course, two ribands are secured on the sliding^
plank, and. strongly shored. Should the ship not move when the
dog-shore is knocked down, the blocks remaining under the fore
part of her keel must be consecutively removed, until her weight
oveicomes the adhesion, or until the action of a screw against her
fore-foot forces her off.
A different mode of launching is sometimes practised in British
merchant-yards, and has been long in use in the French dockyards,
Fig. 15.
allowing the keel to take the entire weight of the vessel. The
two pieces a, a, which arc shown in fig. 15 as being secured to the