sail smooth, sail safe - old dominion universityaverma/nsf/marine kits/ship disaster... · sail...

Includes Basic ship Terminologies and Investigation Check list

Sail Smooth, Sail Safe

Marine Kit – 4 Marine Kit – 4

MarineTech Project, Lean Institute ODU, May 2011

1. Ship Terminology………………………………………………………03

2. Motions of a Floating Body…………………………………………...09

3. Ship Stability…………………………………………………………….10

4. Free Surface Effect……………………………………………………..13

5. Effect of Water Density on the Draft…………………………………15

6. Displacement of Ship…………………………………………………..16

7. Loading of Ship………………………………………………………....17

8. Tanker Ships.…………………………………………………………....19

9. Speed of Ship..…………………………………………………………..20

10.Ship Power Plant………………………………………………………..21

11.SONAR……………………………………………………………………23

12.Unit Conversions……………………………………………………….26

Index

2MarineTech Project, Lean Institute ODU, May 2011

1. Ship Terminology

Starboard

Port

Stern

Bow

Bow : Front part of the ship

Stern : Rear part of the ship

Starboard : Right side of the ship

Port : Left side of the ship3


Hull

•Most of the modern vessels have

double hull to prevent flooding in

case of accidents.

•Tankers have double hull to

prevent oil spilling in case of hull

damage.

•Double hull also serves as

ballast tanks in the partial loaded

or unloaded condition to keep

the center of gravity as low as

possible for stability.

Ship Hull

Hull is a body of a ship

Double Hull4


Keel

http://web.nps.navy.mil/~me/tsse/NavArchWeb/1/module2/introductio

n.htm#

Keel of the ship is the

principal structural

member of a ship running

lengthwise along the

center line from bow to

stern, to which the frames

are attached.

Various terms used to define hull cross section

“fore” is the front part

“aft” is the rear part


Cross section of ship

Draft of a ship is the vertical distance between the waterline and the bottom

of the hull

Draft

FreeboardWaterline

Freeboard of a ship is the vertical distance above the waterline

Beam of a ship is the width of a ship at any cross section

Beam


Deadrise: Deadrise is an angle measured upward from a horizontal plane at

the keel level.

Flat bottomed vessels

have 0 (zero) deadrise.

Deadrise for “V” shaped

hull varies from bow to

stern.

Deadrise is very important feature in the stability of the vessel. A flat

bottomed boat rises on a plane quickly and provides a stable comfortable

ride in calm water – but will pound heavily in rough water. A vessel with

deadrise provides greater stability and comfort in rough conditions.

• Ocean going big ships are never flat bottomed in the fore and aft

hull sections, may be almost flat bottomed in the mid ship section.

• Ocean going vessel with full flat bottomed hull may capsize easily in

the heavy seas

Deadrise


Bulkhead: Bulkhead is a upright wall like structure within the hull of a ship.

• Bulkheads increase structural rigidity of the vessel

• Bulkheads create watertight compartments to prevent flooding in case of

hull breach or leak.

Longitudinal Bulkheads are used to create watertight compartments in

case of ship capsize. It also divides cargo into different sections and thus

helps improve stability of ship by creating different center of gravities for

different sections. (More on this in free surface effect)

Bulkheads

Bulkheads


2. Motions of a floating body

Any floating body has three motions namely Roll, Pitch and Yaw

Roll: Rolling is the motion of a floating body about the longitudinal axis ( axis

along the length of the body)

Pitch: Pitching is the motion about the transverse axis of the body (i.e axis

along the width of the ship.

Yaw: Yawing is the motion of a floating body about the vertical axis.

Control of all the three motions is very important for ship stability and

ride comfort. 9MarineTech Project, Lean Institute ODU, May 2011

3. Ship Stability

Center of Gravity (G), Center of Buoyancy (B), and Metacenter (M)

play very important role in stability of the ship.

The center of buoyancy, is the center of gravity of the volume of water

which the hull displaces. This point is referred to as B in naval

architecture. The center of gravity of the ship itself is known as G in naval

architecture. When a ship is upright, the center of buoyancy is directly

below the center of gravity of the ship.


http://en.wikipedia.org/wiki/Center_of_gravity

http://en.wikipedia.org/wiki/Volume

http://en.wikipedia.org/wiki/Water

http://en.wikipedia.org/wiki/Hull_%28ship%29

http://en.wikipedia.org/wiki/Displacement_%28fluid%29

http://en.wikipedia.org/wiki/Naval_architecture

http://en.wikipedia.org/wiki/Naval_architecture

Center of Gravity is the point where all the weight of the object can be

considered to be concentrated

Center of Buoyancy is the center of mass of the immersed part of ship or

floating object

Metacenter is the point where lines of action of upward buoyancy force intersect

When the ship is vertical, it lies above the center of gravity and so moves in the

opposite direction of the heel as ship rolls

Relationship between G and M

G under M: ship is stable

G = M: ship neutral

G over M: ship unstable

G

M

B

M

G

B

Stable Unstable11MarineTech Project, Lean Institute ODU, May 2011

When the cargo in the ship are evenly distributed, the ship will be

upright. The sum of the gravity forces of cargo and the ship will be

acting at one point - the Center of Gravity, G, acting downwards.

Similarly, the Center of Buoyancy of the ship will be acting at one point

B, acting upwards.

A ship is said to be in Stable Equilibrium if on being slightly inclined,

tends to return back to the original position.

However, a ship will be in Unstable Equilibrium when she tends to move

further from that original position on being tilted slightly. A ship in

Neutral Equilibrium will tend to neither return nor move further from that

position.

What is stable equilibrium?


Wave

• Force of wave heels the

ship to the starboard.

• Center of gravity of oil

shifts.

• Oil acts as a single

mass, hence the

change in the center of

gravity is drastic

• Force of wave and

change in the center of

gravity heels the ship

more and more without

giving it a chance to

come to its upright

position.

• As the ultimate effect of

wave force and big

change in center of

gravity ship capsizes.

4. What is the free surface effect?

This effect proves fatal in partially filled ocean going vessels in the

heavy seas.


Ship is fitted with

compartments, i.e.

(longitudinal bulkheads)

Now the liquid in the

tank acts as different

masses and center of

gravity of individual

mass changes.

But effect of changing

all the center of gravities

does not shift the center

of gravity of the ship as

significantly as before.

How to minimize the free surface effect?

The other way to minimize the free surface effect is to fill the tanks nearly full.

This does not give the liquid room and hence minimizes the free surface effect.

Tanker ships never sail partially filled 14MarineTech Project, Lean Institute ODU, May 2011

5. Effect of change in density of water on

the draft of a ship

Density of Fresh Water = 1000 kg / m3

Average Density of Sea Water = 1030 kg / m3

Draft of ship changes with the change in density of water

NewDensity

OldDensity

OldDraft

Draft New

Keeping the load same, change in the draft can be calculated

by following equation

Fresh water draft is more than salt water draft

Ships transiting between sea water and fresh water have to consider this

change in draft to avoid a danger of running aground15


The word "displacement" arises from the basic physical law, discovered by

Archimedes, that the weight of a floating object equates exactly to that of the

water displaced

6. Displacement of ship

Displacement = actual total weight of the vessel

Unit of Displacement = long ton or metric ton

How to calculate Displacement of ship?

1. Volume of submerged part (cu. Feet) = length * Beam * Draft

2. Multiply this by block coefficient of hull

3. Multiply this figure by 64 to get weight of ship in pounds or divide by

35 to calculate weight in long tons

4. Using SI or metric system: displacement (in tons) is volume (in cubic

meters) multiplied by the specific gravity of sea water (nominally

1.025)


Lightship weight is the

displacement of the ship

only with no fuel,

passengers, cargo, water,

etc. on board.

Deadweight Tonnage

(DWT) is full load

displacement minus the

lightship weight. It includes

the crew, passengers,

cargo, fuel, water and

stores etc.

A ship can carry cargo weighing roughly 90% of its deadweight

tonnage

Full Load Displacement:

Displacement when ship is

loaded with cargo or

people to the point that it is

submerged to its load line

Plimsoll line or International Load Line

the mark on the hull of a ship that shows where the waterline is when the ship

is loaded to full capacity according to the condition of the water at the point

of loading.


7. Loading of Ship

• Cargo should be always evenly distributed

• Uneven distribution makes ship unstable

• Uneven distribution also creates stresses on the ship structure

• Cargo should be properly secured (e.g.in case of cargo like cars)

cargoofMass

cargoofVolumeStowage Factor =

Proper care should be taken to distribute the load evenly

when carrying high density cargo with stowage factor above

0.56


8. Tanker Ships

Slop tanks are provided for storage of dirty ballast residue and tank

washings from the cargo tanks

General Arrangement of Cargo and Ballast Tanks for Tankers

•Tankers are used to carry liquid and gaseous cargo

•All the tanker ships have double hull in order to prevent oil

leakage

•Partially filled tankers are highly unstable in heavy seas

because of the free surface effect


9. Speed of ship

Speed of a ship is measured in knots

• Modern ships are powered by diesel engines

• Some ships are powered by steam turbines also

• Nuclear power is used in defense naval ships

Propellers

Propeller

shaft

Power

Source

(Diesel

Engine /

Steam

Turbine/

Nuclear

power)

Loss of propulsion system can prove fatal, especially in heavy

seas as ship loses control over direction20


10. Ship Power Plant

Most new ships today are powered by diesel engines,

though a few older ships are still powered by steam

turbines and reciprocating steam engines

Propeller

Propeller shaft

Power Plant

(Engine/ turbine)


• Power plant and propulsion system are the most critical

systems in any ship

• It gives the ship the force required to move

• Failure of power plant or propulsion system could be fatal as

ship loses control on the direction

• Loss of power or propulsion in heavy seas or near the shore is

very dangerous since ship may stray with the direction of

winds and waves and may run aground


11. SONAR

SONAR (Sound Navigation and Ranging)

SONAR is a technique that uses sound propagation under water

(primarily) to navigate, communicate or detect other vessels

Principle of SONAR: Reflection of sound waves


24

• A transmitter is used to transmit the signal

• A receiver is used to catch the reflection (echo)

• The time from transmission of a pulse to reception is measured

• Speed of sound in water is known

• Using the formula Speed = we can calculate the distance of

the object from the source of the pulse (transmitter)Time

ceDistan

SEA BED

Distance “d”

Time “t”


Speed of sound in water is calculated using following equation

4388 + (11.25 × temperature (in °F))

+ (0.0182 × depth (in feet)

+ salinity (in parts-per-thousand)).

Speed of Sound

(feet /s)=

1 foot = 0.3048 meters

Distance from the object is calculated using formula

Distance =Speed of sound x time between transmission and reception

2


12. Unit Conversions

1 Metric ton = 2204.62 pounds = 1000 kilogram

1 long ton = 2240 pounds = 1016.05 kilogram

1 meter = 3.281 feet

1 knot = 1.151 miles / hour = 1.852 kilometer / hour

1 nautical mile = 1.151 miles = 1.852 kilometer

746 horsepower = 1 Watt = 1 Joule / second


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