nautical physics

7/31/2019 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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