Download - Nautical Physics
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PHYSICS ON
BOARD
Submitted by:
RUBEN APELACIO Jr.
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A ship made of any material, concrete, steel, wood, or plastic will
only stay afloat while the buoyancy, is greater than its weight. The
buoyancy or upward force from the sea is equal to the weight of the
water displaced. So a 10 ton ship will sink into the water until 10 tons
of water has been pushed aside. Add 5 tons of cargo and it will sit
deeper in the water with 15 tons of water displaced.
The reason for this can best be explained by looking at a ship in a
small harbor with lock gates. As the ship sinks into the water, the
water is pushed sideways and this causes the water level in the dock to
rise, the upward force on the boat is caused by the weight of the water
you have caused to rise trying to get back to a level position. It is the
same force in or out of the dock.
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WHY CONCRETE SHIPFLOAT?
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Concrete as a solid block sinks as it uses up less space than the same
weight of water, when you spread it out on a frame enclosing air, it takes up
a greater space than the weight of the equivalent volume of water and floats.
An old wooden ship, encased in Ferrocement, will usually sit higher in the
water after, and needs to have extra ballast added to bring it back down to itsoriginal level.
The amount of space within the ship above the water line and below the
point water could enter is the reserve buoyancy.
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KEEPING SHIP UPRIGHT
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A large steel ship is designed to be heavier at the bottom than the top, often
the lower part is made of heavy metal, sometimes with ballast (extra weight
added at the bottom) while the upper levels is made of light weight material
such as aluminum. Engines and any other heavy items are kept as low as
possible.
The weight, or force of gravity is pushing down through the center line ofthe ship, and the buoyancy is equal at the same point. When the ship tilts a
little to the side by some means, the buoyancy is in the new center of contact
with the sea, and no longer directly under the center of gravity, it therefore
pushes it back up straight. If the center of gravity is too high or can be made
by some other reason to move outside of the point the buoyancy force is
pressing up, the ship will capsize.
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The side to side rocking motion of a ship is caused by the rise and fall of
waves, when the water is higher on one side the ships center of contact with the
water will be on that side causing the ship to tilt over the opposite way to stay
level in relation to the wave. When waves run across the path of a ship this sets up
a pendulum effect, when you go directly into waves this motion does not occur
but the ship may go up and down in relation to the front and back.
When a ship moves through water it in effect creates mountains in front and a
valley behind, so its nose will rise and back will be lower. The faster you go, and
therefore the more water you move in relation to the size of the craft, the more
marked this becomes. With small speed boats going very fast they can even get tothe point that they will do a backwards somersault. Fast flowing water past a
stationary craft can have a smaller but similar effect.
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STABILIZERS
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Stabilizers are like small wings that stick out below the
waterline. They reduce the side to side motion. They are
most effective then the ship is moving forward though the
water, large gyros, spinning weights, also will reduce or
eliminate the movement.
It is also possible to use the movement of water or
another liquid to level up a container within a ship, or to
control servos that through hydraulics or other meansachieve a stable platform.
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METACENTRIC HEIGHT
This drawing which demonstrates the relative positions of theCenter of Gravity, Center of Buoyancy, and Metacenter
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The metacentric height is a measurement of the initial static stability of a
floating body. It is calculated as the distance between the centre of gravity of a
ship and its metacentre. (GM). A larger metacentric height implies greater
initial stability against overturning. Metacentric height also has implication on
the natural period of rolling of a hull, with very large metacentric heights
being associated with shorter periods of roll which are uncomfortable for
passengers. Hence, a sufficiently high but not excessively high metacentric
height is considered ideal for passenger ships.
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HOW DOES SHIP TURN
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Ships use the principle of recoil for propulsion and steering.
In order to accelerate a mass in a given direction, a force needs to act on this
mass in the direction of acceleration.
According to Newton's third law, if a mass A exerts a force on mass B, mass
B exerts a force of equal magnitude and opposite direction on mass A.
So if the ship (by means of its propeller) exerts a force on the water, the
water exerts a force of equal magnitude on the ship. This recoil force is what
drives the ship ahead.
If the water is forced a bit sideways by the ships rudder, the rudder is forced
sideways in the other direction, again because of recoil, and the ship is
turned.
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ACCELERATION OF SHIP
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In physics, acceleration is the rate of change of velocity with time.In one
dimension, acceleration is the rate at which something speeds up or slows down.
However, since velocity is a vector , acceleration describes the rate of change of
both the magnitude and the direction of velocity. Acceleration has the
dimensions L T2. In SI units, acceleration is measured in meters per second
squared(m/s2). (Negative acceleration i.e. retardation, also has the same
dimensions/units.)
Proper acceleration, the acceleration of a body relative to a free-fall
condition, is measured by an instrument called an accelerometer.
http://en.wikipedia.org/wiki/International_System_of_Unitshttp://en.wikipedia.org/wiki/International_System_of_Units -
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In common speech, the term accelerationis used for an increase in
speed (the magnitude of velocity); a decrease in speed is called
deceleration. In physics, a change in the direction of velocity also is an
acceleration: for rotary motion, the change in direction of velocity
results in centripetal (toward the center) acceleration; whereas the rate of
change of speed is a tangential acceleration.
Proper acceleration, the acceleration of a body relative to a free-fall
condition, is measured by an instrument called an accelerometer.
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In common speech, the term accelerationis used for an increase in speed (the
magnitude of velocity); a decrease in speed is called deceleration. In physics, a change in
the direction of velocity also is an acceleration: for rotary motion, the change in
direction of velocity results in centripetal (toward the center) acceleration; whereas the rate
of change of speed is a tangential acceleration.
In classical mechanics, for a body with constant mass, the acceleration of the bodyis proportional to the net force acting on it (Newton's second law):
where F is the resultant force acting on the body, mis the mass of the body, and a
is its acceleration.
Average acceleration is the change in velocity (
v) divided by the change in time(t). Instantaneous acceleration is the acceleration at a specific point in time which is
for a very short interval of time as tapproaches zero.
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INERTIAL NAVIGATION
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An inertial navigation system (INS) is a navigation aid that uses a
computer, motion sensors (accelerometers) and rotation sensors (gyroscopes) to
continuously calculate via dead reckoning the position, orientation, and velocity
(direction and speed of movement) of a moving object without the need for
external references. It is used on vehicles such as ships, aircraft, submarines,
guided missiles, and spacecraft. Other terms used to refer to inertial navigation
systems or closely related devices include inertial guidance system, inertial
reference platform, inertial instrument, inertial measurement unit (IMU) and
many other variations.
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GLOBAL POSITIONINGSYSTEM
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GPS (global positioning system) can be defined as a collection of satellites
and ground stations that allow users with specifically designed radio equipment
to obtain position, distance and velocity data. Mariners at one time used
constellations and the stars (such as Polaris in the Little Dipper or Alpha Ursae
Minoris) as landmarks at night to determine their position and direction at
sea. GPS replaces natural stars with artificial satellites which, together with
radio signals and computer chips, have taken navigation a quantum leap forward
in accuracy and usability.
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APPLIED PHYSICS
ENGINE
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An oscillating engine was a type of direct-acting engine that was designed
to achieve further reductions in engine size and weight. Oscillating engines
had the piston rods connected directly to the crankshaft, dispensing with the
need for connecting rods. In order to achieve this aim, the engine cylinders
were not immobile as in most engines, but secured in the middle by trunnions
which allowed the cylinders themselves to pivot back and forth as the
crankshaft rotated, hence the term oscillating.[24] Steam was supplied and
exhausted through the trunnions. The oscilating motion of the cylinder was
used to line up ports in the trunnions to direct the steam feed and exhaust to
the cylinder at the correct times
http://en.wikipedia.org/wiki/Marine_steam_enginehttp://en.wikipedia.org/wiki/Marine_steam_engine -
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APPLIED PHYSICS
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Apropeller is a type of fanthat transmits power by converting rotational
motion into thrust. A pressure difference is produced between the forward
and rear surfaces of the airfoil-shaped blade, and a fluid (such as air or
water) is accelerated behind the blade. Propeller dynamics can be modeled by
both Bernoulli's principle and Newton's third law. A propeller is often
colloquially known as screw.
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