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Stability Terms > Stability Terms Chief Mate 3000 > Flashcards

Stability Terms Chief Mate 3000 Flashcards

1
Q

Stability

A

The ability of a vessel to return to the upright position when inclined from upright by external force. If she returns to upright she is stable (stable equilibrium). If she has no tendency to return upright she is neutral (neutral equilibrium). If she flips over further she is unstable (unstable equilibrium).

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2
Q

Light Displacement

A

Weight at light draught. Water in engine, cooling system and fuel in engine tank, but no fuel or water in tanks, no cargo, no crew or stores onboard.

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3
Q

Displacement

A

Weight of vessel at any given draught, including everything onboard.

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4
Q

Load Displacement

A

Displacement at load draught.

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5
Q

Deadweight

A

The weight of everything onboard that is not part of the light displacement. (Cargo, fish, fuel, water, stores and crew)

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6
Q

Draught

A

Vertical distance from the waterline to the bottom of keel.

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7
Q

Freeboard

A

Distance from the waterline to the lowest watertight deck. We are usually interested in minimum freeboard which is aft.

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8
Q

Density

A

Relationship between weight and volume. Defined by ‘mass per unit volume’. Eg. 1 metric tonne of fresh water=1m3 and therefore has a density of 1 tonne/m3.

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9
Q

Law of Floatation

A

When a vessel floats, the weight of the vessel is supported by the buoyancy of the water. It displaces a weight of water equal to the weight of the vessel.

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10
Q

Relative Density

A

Defined as the ratio of the weight of the substance to the weight of an equal volume of fresh water.

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11
Q

Freshwater Allowance

A

A vessel’s underwater portion of hull is smaller in seawater than fresh water and therefore sinks more in fresh than sea water. Ie. less draughts in sea water. The difference between the two draught a is called fresh water allowance.

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12
Q

Trim

A

Difference between draught froward and aft.

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13
Q

Centre of Gravity

A

Where a vessel’s weight acts vertically downwards.

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14
Q

Centre of Buoyancy

A

Where buoyant forces of water act vertically upward.

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15
Q

Buoyancy

A

An upward force exerted by a fluid that opposes the weight of an immersed object.

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16
Q

Reserve Buoyancy

A

The part of the volume of a ship which is above the water surface and is watertight, so that if a ship sinks more, the buoyancy will increase. Usually from the waterline to the first deck.

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17
Q

Righting Lever

A

Where a heeled vessel forms a lever to bring her upright. The horizontal separation between forces of gravity and buoyancy.

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18
Q

Loll

A

Unstable but not capsized, settled at an angle of loll.

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19
Q

KG

A

Vertical centre of gravity.

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20
Q

KGf

A

Vertical centre of gravity corrected for free surface.

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21
Q

KMt

A

Height of transverse meta centre above the baseline.

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22
Q

FSM

A

Free surface moment of a partially full tank is an apparent vertical moment caused by free surface in the tank.

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23
Q

LCG

A

Longitudinal centre of gravity is the horizontal distance of the centre of gravity from amidships.

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24
Q

LCB

A

Longitudinal centre of buoyancy is the horizontal distance of the centre of buoyancy from amidships.

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25
Q

LCF

A

Longitudinal centre of Floatation is the horizontal distance of the centre of floatation from amidships.

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26
Q

TPC

A

Tonnes per centimetre immersion is the number of tonnes that must be loaded/unloaded to change the vessels draught by 1cm.

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27
Q

MTC

A

Moment to change trim. The number of metric tonnes it takes to change trim by 1cm. Found in the hydrostatic table.

28
Q

Angles of Flooding

A

The angle the sill or coamings of opening, in or above the freeboard deck first reach the water level.

29
Q

Actual Angles of Flooding

A

The angle of heel an opening that cannot be closed or made weathertight becomes immersed.

30
Q

Potential Angle of Flooding

A

If an opening is fitted with a weathertight closing device which can be kept closed and secured at all times when the vessel is underway or at sea, then progressive down flooding can only occur through that opening if the closing device is not closed and secured.

31
Q

Archimedes Principle

A

A body which is wholly or partially immersed in a fluid will experience an up thrust or loss of weight equal to the mass of the fluid displaced.

32
Q

What Is The Relative Density of Fresh Water?

A

1.000

33
Q

What Is The Relative Density of Sea Water

A

1.025

34
Q

List

A

Caused by internal force. Unequal moments about G.

35
Q

Moment

A

A weight x distance.

36
Q

Pro-Metacentre

A

M at a roll more than 15 degrees.

37
Q

Min Distance Between M and G: Fishing Vessel

A

0.35m

38
Q

Min Distance Between M and G: Other Than Fishing

A

0.15m

39
Q

GZ

A

Righting lever. The higher G, the less the righting lever. The lower G, the more the righting lever.

40
Q

GM

A

Metacentric height.

41
Q

t/m

A

Tonne meters.

42
Q

Negative GM

A

M is below G. Unstable.

43
Q

Positive GM

A

M is above G. Stable.

44
Q

Stiff Ship.

A

Big righting lever. Fast return to upright.

45
Q

Tender Vessel

A

Small positive GM.

46
Q

Distance of 1 Roll.

A

From beam back to same beam.

47
Q

Amending an Angle of Loll

A

Angle of loll is at around 20 degrees. We must lower the centre of gravity. Move high things low. Throw cargo off the high side. Press up ballast tank on downward side as close to centre of K as possible, then press up the tank closest to the centre of K on the higher side. We must avoid free surface. Do one thing at a time.

48
Q

ρ

A

Density

49
Q

Δ

A

Displacement

50
Q

Aw

A

Water-plane area.

51
Q

Gross Tonnage

A

Function of moulded volume of all enclosed spaces of a vessel. Indicates overall size of the ship.

52
Q

Net Tonnage

A

Function of moulded volume of all cargo spaces. Indicates useful capacity of a ship.

53
Q

1 Radian

A

57.3 degrees.

54
Q

What is the Measure of Freeboard?

A

From the waterline to the top of the deck line.

55
Q

Fluid

A

The term used for all liquids, water, fuel etc in stability.

Definition: A substance (such as a liquid or gas) tending to flow or conform to the outline of its container.

56
Q

Pressed Up Tank

A

A tank that is completely full.

57
Q

Slack Tank

A

A tank that is not full and not empty. Partially full.

58
Q

LBG

A

Longitudinal distance between B and G.

59
Q

LBP

A

Length between perpendiculars.

60
Q

BG

A

Trimming lever

61
Q

Surging

A

Brief additional forward motion due to rise and fall of sea surface.

62
Q

Heave

A

Brief vertical motion due to rise and fall of sea surface.

63
Q

Sway

A

Brief sideways motion along the slope of the sea surface.

64
Q

6 Degrees of Freedom

A 
Roll
Pitch
Yaw
Surge
Sway
Heave
65
Q

Hogging

A

Longitudinal stress. Ships hull bending upwards at mid ships.

66
Q

Sagging

A

Longitudinal stress. Hull bending downwards at mid ships.

67
Q

Shearing

A

Longitudinal stress. Caused by vastly different forces on either side of a bulkhead.

Stability Terms (1 decks)

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