A LECTURE ON SHIP-BUILDING.
"We are not ship-builders, boys; in fact, there is not a ship-builder
connected with the school, and I do not intend to engage one even as an
instructor," said the principal, continuing his remarks on the platform.
"In the present depressed state of this important industry, perhaps it
is not advisable to devote much time to the study of scientific
construction in ship-building. It looks now as though the ships of the
future were to be of iron; and many vessels of this material are built
in this country at the present time.
"But perhaps ship-building is rather too ambitious a term to apply to
our intended operations. We shall build a boat of considerable size, and
while we are doing the work we shall learn what we can about
ship-building. Many years ago I built a ship for myself, and
superintended its construction from the keel to the trucks. In building
our boat we shall not put in every stick used in a ship.
"Did any of you ever tow a log in the water?" asked the principal,
pausing for a reply.
"I have," answered Leo Pownall, whose father owned a saw-mill. "I have
towed lots of them on the mill-pond."
"To which end of the log did you make fast?" inquired the captain.
"To either end; just as it came handy," replied the student.
"Then you sometimes did more work than was necessary with your oars. A
log tows easier when you make fast to the big end," continued the
principal, waiting for the pupils to digest the idea.
"I don't see what difference it can make," added Leo. "If anything, I
should say that the small end would open a passage through the water
more readily than the big end."
"I suppose none of you ever saw a whale, but most of you have caught
horn-pouts, or bullheads."
"I have seen a whale on exhibition in New York," interposed Luke
Bennington.
"What was the shape of his head?"
"The one I saw was round; but I have seen pictures of whales in which
the head was nearly square."
"How is it with the pout!"
"His mouth is about the widest part of him," laughed Alick Hartford.
"Take fishes in general, in what part of the body do you find the
greatest girt?" asked the principal.
"Just astern of the head," replied Kit Burlington.
"In some fishes, about one third of the length from the mouth," added
Bark Duxbury.
"Very good; you are about right, though some fishes vary from the
general rule. Now don't you think Nature made a mistake, Leo Pownall,
and that fishes ought to swim tail first instead of head first, as you
would tow a log?"
"I suppose God made the fishes all right; but He gave some of them very
sharp noses," returned the saw-mill owner's son.
"Corresponding to the shape of the butt of a log after it has been
felled; but the greatest girt is still near the head. This is the
general shape of the hull of a vessel."
"But the head of a sperm whale is almost square; and no other fish is
like him," added Phil Gawner.
"The whale is not a fish, Gawner. I have seen a school of porpoises
alongside an ocean steamer. Their greatest girt is one third of the
length from the head end; but they will swim past a fast steamer, and
make something like twenty knots an hour," said Captain Gildrock.
"I was trying to find the porpoise in Wood's Natural History the other
day; but there is no such fish in the book," added Sol Guilford.
"Where did you look?"
"In the volume about fishes."
"The porpoise is not a fish, and you would have found it in the volume
marked 'Mammalia,'" replied the principal with a smile.
"But isn't the porpoise a fish? He lives in the water."
"So do hippopotami; but they are not fishes. Whales, porpoises,
dolphins, seals, and some others, are mammals; that is, they suckle
their young as a cow does a calf. Properly they are not fishes, though
they are very often called so."
These were the kind of questions the captain believed in encouraging,
though they sometimes led the conversation out of the legitimate
channel. They elicited useful information; and he was careful not to let
the students wander too wide of the subject under discussion.
"I don't know now why a log or a fish goes best with the big end
ahead," said Leo Pownall.
"After the passage for a moving body in the water is opened, this fluid
follows its own laws, and seeks an equilibrium. As it moves back to its
natural level, it crowds in upon the after part of the body, whether it
be a log, a fish, or a ship, and thus pushes it ahead. Under the stern
of a vessel, the hull is curved, or hollowed out, just as the size of a
fish diminishes at the tail, which is the fish's rudder.
"But the shape of the hull is varied according to the use to which the
vessel is to be put; but the rule will hold good in the main. In
building a ship the beginning of the work is done on paper. As in
erecting a house, the first thing is to obtain the plans, which are made
by the naval architect. In fact, the entire shape of the vessel is laid
down on the drawing-board. From these the builder gets his dimensions,
all the curves, and the form of every timber and piece of wood used.
"On the drawing on the wall," continued the principal, taking the
pointer and indicating the plans, "everything is put down that can be
needed in the construction of the boat we intend to build. There are
three plans, you will observe. I had them drawn by a naval architect in
New York. This," and the principal pointed to the highest one on the
paper, "is the sheer plan. It shows the side or profile of the hull on a
flat surface. It looks just as the broadside of the Sylph would, if she
were too far off for you to get any idea of the curves in her sides.
"This plan gives the exact curve of the bow, and the exact slant of the
stern-post. The three straight lines extending the whole length of the
hull are the levels to which the water would stand if the vessel were
submerged to three different depths. This drawing is made on a scale of
one inch to a foot. The sheer plan is a vertical plane through the keel.
From it we get the length and height. The red lines which extend from
certain points at the bow to the lower part of the stern post indicate
the various curves of the hull at different distances from the vertical
plane of the keel. In other words, they are three vertical planes,
parallel with the central plane.
"The next plan, of the same length as the first, shows you one half of
the deck of the boat, and is called the half-breadth plan. All the plans
are on the same scale. The straight lines on the deck are the curved
lines of the sheer plan, or the tops of the several vertical planes.
This plan reversed would show the other side of the vessel.
"The third is the body plan, and exhibits a vertical section of the
hull, looking at it end-on, at the point where it has the greatest
breadth. The right-hand half of it shows the bows, and the left the
stern. The curved lines are the same as those on the sheer plan, though,
of course, they are shown only at the bow and stern, for you cannot see
a line when you look end-on.
"With the making of these plans the task of the naval architect comes to
an end, unless he is employed to superintend the construction of the
vessel. From the plans the builder gets the exact size and shape of the
craft he is to build. From it the moulds, or patterns, of all parts of
the hull are made. In an apartment called the moulding-room, with which
every ship-yard is provided, full-sized plans of the vessel are drawn on
the floor. I do not mean that the entire ship is drawn at the same time.
"If the bow or stern was accurately transferred to the floor, enlarged
to the actual size of the hull, the exact form of the stem or stern post
could be marked off. From this, a mould or pattern could be made of
board or plank. As a matter of fact, a mould is made for every part
used in the construction of the ship, not every piece of wood, for what
is used for one side may do just as well for the other side. For
example, a timber on one side is exactly like the one on the opposite
side.
"In ship-building, the word timber has two meanings. As in general use,
it may be any large stick of wood. In the technical sense, it is one of
the ribs of the vessel. The means of understanding which is meant will
be given you as you proceed with the work. The keel is the backbone of
the vessel, and the strength of the hull depends largely upon it.
"The keel corresponds with the backbone of your bodies. At the forward
end of it is the stem, shaped as you see in the sheer plan. At the after
end is the stern-post; and these three parts form the profile of the
vessel. Between them are the timbers, or ribs, curved as required by the
shape of the hull. To the timbers, the stem and stern-post, the
planking, or outer skin of the ship, is fastened. If you were to build a
canvas canoe, you would make a frame such as I have described. The cloth
part would correspond to the planking.
"But, besides the principal parts I have mentioned, of course there is
a vast number of other parts, whose names you could not remember if I
gave them to you. I shall add only a few of the principal ones. The
timbers--I use the word in its technical sense--are set up about three
feet apart, sometimes a little more, and sometimes a little less. The
lower end of each is fastened to the keel, and of course each timber has
to be shored up, and carefully secured in its proper position.
"The timbers are at right angles with the keel, and in large vessels are
formed of several pieces. Across the keel is laid the floor timber,
which is the connecting link between the pair of ribs. In the middle of
the ship, the floor is nearly flat; but near the stern-post the timbers
strike the keel at an acute angle, and in the same manner at a less
angle at the bows.
"Above the floor timbers is laid the keelson, which is a large and
strong timber a foot square or more in large vessels. These pieces are
fitted together, and bolted to the keel through the timbers. The sharp
angle at the stern is filled with solid wood. As you have seen, the
floor timbers are parts of the ribs," continued the principal, pointing
to a diagram of a full rib. "The next two sticks, forming the sharpest
bend in the timber, are the futtocks, above which are the top timbers
and the lengthening pieces. The plankshear is placed on the top of the
timbers, extending from bow to stern, even with the upper deck, if there
is more than one.
"Large ships have two, three, and even four decks. Fastened to the
timbers are pieces called shelves, upon which rest the beams or timbers
extending across the ship, upon which the decks are laid. In the
corners, where the beams join the ribs, are placed the knees (timbers
like brackets) in which the angle is formed by the natural growth of the
wood. Of course all these pieces are bolted together in the strongest
manner.
"The timbers next to the stem are the knight-heads. They extend upwards
higher than the tops of the other ribs, and assist in the support of the
bowsprit. In the keel, stem, and stern-post, a rabbet, or triangular
groove, is cut out, into which the planks are extended. The first course
of the planking, next to the keel, whether composed of one or many
pieces, is called the garboard streak. This word is often written
_strake_. The other word is more commonly used in this country.
"The next coarse above the garboard streak is the bilge streak, which
may consist of several widths of plank. Above there are the wales, and
still higher the shear streaks. Some of these terms are applied to the
parts of the ship as localities. The bilge is where the sharpest bend
comes in the hull; the wales are the sides near the load line.
"I have tried to give you a general view of ship-building, with a few of
the more important technical terms, some of which most of you have
learned before. As I have said, we shall not use all these pieces in
building the boat. For example, a false keel is put under the true keel
of a ship. It is a timber of the toughest wood, from four to six inches
thick, which is bolted to the keel after the keelson is secured. It is
but lightly fastened, for it is intended to come off, if the vessel
strikes a shoal, and thus allow the true keel to slide off. We shall not
need this addition, unless we require it to increase the depth of the
keel. In that case, it would be better to have the part corresponding to
the false keel made of lead or iron, and then it will serve as so much
ballast.
"On the table you see a wooden model of the boat we are to build. Its
form and size are exactly indicated by the three plans I have
explained. We are not ship-builders, only amateurs; and, while I shall
take pains to have you understand the theory and practice of the art, I
do not feel obliged to follow all the methods in use. So far as I know,
no such model as the one on the table was ever made before. As I shall
direct the construction of the boat, I shall do it in my own way, though
it may not be according to the accepted rules.
"I have kept you now longer than I intended, for, after the hard work
you did last night, and the very quiet and business-like way in which
you did it, I shall make the rest of the day a holiday. The Beech Hill
fleet is at your service, and you may spend the day in any proper manner
that you please. To-morrow afternoon we will dissect this model, and
give out the work of building the boat. In the meantime I shall be glad
to receive suggestions as to her name; but no student must send in more
than one name, for I wish you to have decided opinions."