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General Ship Knowledge. OOW, MCA > Stability > Flashcards

Stability Flashcards

1
Q

A solid block of material has am ass of 6.2tonne and occupies 2.4m3
Calculate its density, show working

A

Density= Mass / volume

6.2t/2.4m3 = 2.6tonnes/m3

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2
Q

A steel plate 5m x 2m x 5cm and density 7.8t/m3 is to be lifted by a crane calculate the mass of the plate?
Show working

A 
Volume = length x breadth x depth 
Volume = 5mx2mx0.05m= 0.5m3
Mass = density x volume (tonnes)
Mass = 7.8tonnes/m3 x 0.5m3

Mass = 3.9 tonnes

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3
Q

What is the density of Fresh water (FW)?

A

1t/m3

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4
Q

What is the density of sea water (SW)?

A

1.025t/m3

(In practice the density of sea water will vary with many factors. A standard value has been adopted and this should always be used unless told otherwise)

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5
Q

Distinguish between the terms density and relative density ?

A

Density is mass divided by volume and has units of t/m3 or kg/m3

Relative density is a ratio
and is comparison between the density of a substance and density of fresh water. As a ratio it has no units

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6
Q

Oil has a RD of 0.89. Give the density in kg/m3 and t/m3

A

890kg/m3

0.890t/m3

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7
Q

A rectangular tanks is 12m wide, 8m long and 4m deep. Calculate the mass of oil (RD 0.84) in the tank when it is 98% full?
Show working!

A

12x8x4x0. 98x0.84=

316. 1t

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8
Q

Describe the marine hydrometer and how it is used?

A

It consists of a weight bulb and long stem

Which, for marine use, is graduated from just above and below the density of sea and fresh water respectively

The RD is measured by placing the instrument in the liquid and noting the level which it sinks.

The denser the water the higher the hydrometer will float. The correct reading is that corresponding to the plane of intersection of the horizontal liquors surface and stem, I.e allow for the meniscus effect

(Measure from the bottom of the meniscus)

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9
Q

Explain the term KG

A

KG

Is the distance from the KEEL to the CENTRE OF GRAVITY of the vessel

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10
Q

Explain the term LCG?

A

LCG is the horizontal distance of the centre of gravity measured from the aft perpendicular

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11
Q

explain the term Kg

A

Is the height of the centre of gravity of an object or mass on the vessel, measured vertically up from the keel

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12
Q

Explain the term KB

A

Is the distance from the keel to the centre of gravity

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13
Q

State the effect that free surface has on vessels stability

A

Free surface effect
Pushes G upwards which
Increases KG therefore reduces GM (IMPORTANT**)

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14
Q

Define the term meta centre and meta centric height

A

Meta centre is the point where the force of buoyancy intersects the centre line of the vessel

Meta centric height is the distance between the centre of gravity and the meta centre otherwise known as GM

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15
Q

What are the three states of equilibrium

A

Stable
Neutral
Unstable

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16
Q

State three items of information given on the hydrostatic data and explain their use?

A

TPC - tonnes per center meter. Gives the number of tons required to sink or raise a vessel by 1 cm.

KMT - gives the height of the meta centre above the keel. This can be used with the KG of the vessel to determine the GM

Displacement - give the mass of the vessel at given drafts. It can be used to determine the change in draught when masses are added or removed from the vessel

17
Q

Describe the motion and list the advantages and disadvantages for a vessel said to be -

Stiff

A

large GM

Will have fast roll periods to relatively small angles of heel

Advantages-
Resistance to heel, small movements of G will have minimal effect, loss of stability due to a compartment flooding will have a smaller effect of the vessel’s stability.

18
Q

Describe the motion and list the advantages and disadvantages for a vessel said to be -

Tender

A

Small GM

Will roll to large angled but have a longer roll period

Advantages - roll motion is slow so more comfortable for passengers, less violent motion

Disadvantages - little resistance to heel, small movements of G will have a greater effect on the overall stability of the vessel.
Flooding of a compartment will have a serious impact on the stability of the vessel.

19
Q

Explain how the effect of free surface can be reduced?
A)at the design stage?
B)when at sea

A

By designing tanks containing liquids to be long and narrow rather than short and wide

When at sea drain down swimming pools and jacuzzis

20
Q

Define light displacement

A

The mass of their vessel when completely empty

WITHOUT
Crew, passengers, stores, fuel or water

21
Q

Define load displacement

A

The mass of the vessel when

FULLY stored ready for sea and floating at the summer load line or datum load line (100%loaded condition)

22
Q

Define load deadweight

A

The difference between the load and light displacements. The “lift” capacity of the ship

23
Q

Define - Archimedes principle (NEED TO KNOW!)*****

A

Any body wholly or partially immersed in a fluid experiences an upward force equal to the weight of the fluid displaced.

24
Q

Equation to find the mass of water referring to Archimedes principle?

A

Mass of water =

Volume x density

25
Q

Density =

A

Mass divided volume.

Density = p (Greek letter)

Steel has a density of 7.8t per m3

26
Q

Dock water density range?

A

1.001 - 1.024 t/m3

1001 - 1024 kg/m3

27
Q

The force of buoyancy is equal to (Archimedes principle)

A

Volume x density

28
Q

Deadweight = (as an equation)

A

Load displacement - light displacement

29
Q

Define TPC immersion

A

tonnes per cm immersion - the mass required to be added (or removed) to cause 1cm sinkage (or rise)

Sinkage (or rise) =

Mass added (or removed) divided by TPC

TPC has units of tonnes per cm, and mass is measured in tonnes.

What will the units of sing

30
Q

TPC formula

A

Mass divided by TPC

31
Q

Where is the center of buoyancy located ?

A

Is located at the overall centre of the underwater volume of the vessel (IMPORTANT)

32
Q

Where is the centre of gravity located ?

A

Located at the overall centre of mass of the vessel and her contents .

33
Q

Three vital rules with the movement of the center of gravity

A

When mass is ADDED to the yacht, G moves TOWARDS the added mass

When mass is REMOVED to the yacht, G moves AWAY from the added mass

When mass is MOVED to the yacht, G moves in the SAME DIRECTION the added mass

34
Q

Formula to find GM (metacentric height)

A

KM - KG

Distance from keel to the meta centre

Minus

The distance from the keel to the centre of gravity

35
Q

Ways to reduce free surface effect?

A

Press tanks! (Or empty)
empty swimming pool, spas
Long narrow tanks
Wash head bulkheads (bulkheads with ovals/circles cut in them

36
Q

Equation to find the righting moment ?
RM
(The moment of statically stability?)

A

GZ multiplied by displacement
(Value in tonne meters TM)
(∆ x GZ)

37
Q

Neutral stability is when

A

Gravity and metacenter are

General Ship Knowledge. OOW, MCA (4 decks)

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