CHAPTER LEARNING OBJECTIVES
Upon completion of this chapter, you should be able to do the following:
l Explain the use of levers when operating machines afloat and ashore.
l Discuss the classes of levers.
Through the ages, ships have evolved from crude
rafts to the huge complex cruisers and carriers of todays
Navy. It was a long step from oars to sails, another long
step from sails to steam, and another long step to todays
nuclear power. Each step in the progress of shipbuilding
has involved the use of more and more machines.
Todays Navy personnel are specialists in operating
and maintaining machinery. Boatswains operate
winches to hoist cargo and the anchor; personnel in the
engine room operate pumps, valves, generators, and
other machines to produce and control the ships power;
personnel in the weapons department operate shell
hoists and rammers and elevate and train the guns and
missile launchers; the cooks operate mixers and can
openers; personnel in the CB ratings drive trucks and
operate cranes, graders, and bulldozers. In fact, every
rating in the Navy uses machinery sometime during the
Each machine used aboard ship has made the
physical work load of the crew lighter; you dont walk
the capstan to raise the anchor, or heave on a line to sling
cargo aboard. Machines are your friends. They have
taken much of the backache and drudgery out of a
sailors lift. Reading this book should help you
recognize and understand the operation of many of the
machines you see about you.
WHAT IS A MACHINE?
As you look about you, you probably see half a
dozen machines that you dont recognize as such.
Ordinarily you think of a machine as a complex
device-a gasoline engine or a typewriter. They are
machines; but so are a hammer, a screwdriver, a ships
wheel. A machine is any device that helps you to do
work. It may help by changing the amount of force or
the speed of action. A claw hammer, for example, is a
machine. You can use it to apply a large force for pulling
out a nail; a relatively small pull on the handle produces
a much greater force at the claws.
We use machines to transform energy. For example,
a generator transforms mechanical energy into electrical
energy. We use machines to transfer energy from one
place to another. For example, the connecting rods,
crankshaft, drive shaft, and rear axle of an automobile
transfer energy from the engine to the rear wheels.
Another use of machines is to multiply force. We
use a system of pulleys (a chain hoist, for example) to
lift a heavy load. The pulley system enables us to raise
the load by exerting a force that is smaller than the
weight of the load. We must exert this force over a
greater distance than the height through which the load
is raised; thus, the load will move slower than the chain
on which we pull. The machine enables us to gain force,
but only at the expense of speed.
Machines may also be used to multiply speed. The
best example of this is the bicycle, by which we gain
speed by exerting a greater force.
Machines are also used to change the direction of a
force. For example, the Signalmans halyard enables
one end of the line to exert an upward force on a signal
flag while a downward force is exerted on the other end.
There are only six simple machines: the lever, the
block, the wheel and axle, the inclined plane, the screw,
and the gear. Physicists, however, recognize only two
basic principles in machines: those of the lever and the
inclined plane. The wheel and axle, block and tackle,
and gears may be considered levers. The wedge and the
screw use the principle of the inclined plane.
When you are familiar with the principles of these
simple machines, you can readily understand the