Stability

Front 1

Light Displacement

Back 1

Weight of the hull, engines, spare parts and water in the boilers and condensers to working level.

Hint 1

Ship when built (hull and machinery)

Front 2

Load Displacement

Back 2

Weight of the hull and everything on board when floating at any particular draught.

Front 3

Deadweight

Back 3

Difference between the load displacement and the light displacement i.e. the weight of cargo, fuel, FW, ballast, stores, crew, passengers and effects.

Front 4

Summer Load Displacement

Back 4

The weight of the hull and everything on board when at the summer loadline mark.

Front 5

Centre of Gravity (G)

Back 5

This is the point at which the entire weight of the vessel is said to act downwards. Its value is equal to displacement. The position of G is entirely dependent on the weight distribution within the vessel.

Front 6

Draught

Back 6

The depth of the vessel measured from keel to waterline.

Front 7

Freeboard

Back 7

The distance from the freeboard (uppermost complete) deck to the waterline.

Front 8

Initial Transverse Metacentre (M)

Back 8

It is the point of intersection of the vertical through B when the vessel is upright and in the slightly inclined positions. M may be considered to be a fixed point up to an angle of 15°.

Front 9

Initial Metacentric Height (GM)

Back 9

It is the distance measured along the centreline between G and M in the initial upright position. GM is often used as a measure of the stability of a vessel and can be calculated by GM=KM-KG.

Front 10

Height of the Metacentre (KM)

Back 10

It is the height of M above the keel. Note that KM=KB+BM.

Front 11

Centre of Buoyancy (B)

Back 11

The geometric centre of the underwater volume. It is the point at which the vessel buoyancy is said to act vertically upwards. Its value is equal to displacement.

Front 12

Density

Back 12

Mass per unit volume and has this formula.

Front 13

LCF

Back 13

Longitudinal centre of flotation. It is the geometric centre of the waterplane area (at that draught.)

Front 14

Trim

Back 14

The difference between the forward and after draughts.

Front 15

Change of Trim (COT)

Back 15

The difference between the original trim and the final trim.

Front 16

LCB

Back 16

Longitudinal centre of Buoyancy. The point longitudinally, where all the upthrusts due to buoyancy may be considered to act vertically upwards.

Front 17

LCG

Back 17

Longitudinal centre of Gravity. The point longitudinally, through which the total weight (mass) of the vessel may be considered to act vertically downwards.

Front 18

TPC

Back 18

Tonnes per centimetre immersion. The TPC for any draught is the weight a vessel must load or discharge to change the mean draught by 1cm in SW.

Front 19

MCTC

Back 19

Moment to change trim 1cm.

Front 20

Free Surface Effect (FSE)

Back 20

The difference between the actual GM and the effective GM is the virtual loss of GM or FSE.

Front 21

Stable Equilibrium

Back 21

A vessel is said to be in stable equilibrium if, when inclined to a small angle of heel by an external force, she tends to return to the initial position.

Front 22

Neutral equilibrium

Back 22

A vessel is said to be in neutral equilibrium if, when inclined to a small angle by an external force, it tends to remain at that angle.

Front 23

Unstable equilibrium

Back 23

A vessel is said to be in unstable equilibrium if, when inclined to a small angle of heel by an external force, it tends to heel over further.

Front 24

Angle of Loll

Back 24

The angle to which a vessel with a negative initial metacentric height will lie at rest in still water.

Front 25

List

Back 25

A vessel is said to be listed when inclined by an internal force. G is off the centreline.

Front 26

Heel

Back 26

A vessel is said to be heeled when inclined by an external force. G is on the centreline.

Front 27

FWA

Back 27

Fresh Water Allowance. The number of mm by which the draught changes when a vessel passes from FW to SW and vice versa at the loaded draught i.e. at the loadline marks.

Front 28

DWA

Back 28

Dock Water Allowance. The number of mm by which the draught changes when a vessel passes from dock water (DW) to SW and vice versa at the loaded draught.

Front 29

Cw

Back 29

Coefficient of waterplane area is the ratio between the actual waterplane area Aw and that of a rectangle of the same extreme dimensions.

Front 30

Cb

Back 30

Block coefficient is the ratio between the underwater volume and the volume of the block having the same extreme dimensions.

Front 31

Archimedes Principle

Back 31

An immersed or partially immersed body experiences an upthrust (Force of Buoyancy) which is equal to the weight of water displaced, which is equal to the weight of the body.