STABILITY

### Explain density.

Density is the mass of a substance (expressed in kg) per unit of volume. The standardized unit of volume is the cubic metre (m3). The density unit is therefore kg/m3.

### Explain specific gravity.

### Explain the difference between mass and weight.

The mass of a body or a substance is a value that represents the quantity of matter of the body or substance. The mass will not change if the body is placed on the moon, the top of a mountain or at sea level.

### Explain displacement.

### Explain displacement volume.

### Explain draft.

### Explain deadweight.

### Explain lightship displacement.

### Explain loaded displacement.

### Explain waterplane area.

### Explain amidships.

### Explain lightship weight.

### Explain Archimedes' principle.

When a ship is floating freely at rest, the mass of the ship (displacement, Δ) is equal to the mass of the volume of water displaced by the ship.

### Explain the Coefficient of fineness.

Coefficient of fineness of the waterplane area (Cw): This coefficient (variable according to the ship's draft) can be expressed as the ratio of the waterplane area to the area of a rectangle having the same length and breadth.

### Explain the Block coefficient.

Block coefficient (Cb): Coefficient (variable according to the ship's draft) that represents the ratio of the underwater volume of a ship to a rectangular block having the same length, breadth and depth.

### Explain Tonnes per centimetre (TPC) immersion.

TPI = Tonnes per inch immersion

### Explain the effects on a ship's draft from changes in the specific gravity of water

Δ = × ρ

### Explain Fresh Water Allowance (FWA).

### Explain Transverse statical stability.

### Explain the reference point K.

Reference point K is applied to the ship's lowest point, which is the keel. This is a fixed point.

### Explain the centre of gravity G.

### Explain the effects of changing load.

### Explain the centre of buoyancy B.

### Explain Ship's inclination.

### Explain Righting moment.

### Explain Righting lever (GZ).

MSS = Δ ×GZ

GZ = GMsinΘ.

Θ being the ship's angle of inclination.

### Explain Metacentre (M).

### Explain Metacentric height (GM).

### Explain a Righting moment with a reduced GM.

The position of G in relation to M is crucial in a ship's ability to right itself. Under normal conditions, G should always be below M. The GM is then said to be positive. The greater the distance between these two points, the higher the positive GM. As stated in the previous paragraph, the larger the GM, the larger the righting lever. If G approaches M, the righting lever decreases and the righting moment is weak.

### Explain a Neutral equilibrium when GM = 0

If GM is zero, meaning that G coincides with M, the righting lever is non-existent. If an external force then makes the ship heel to a small angle, the ship will remain heeled at this angle because there is no righting moment.

### Explain Capsizing moment with a negative GM.

If GM is negative, meaning that G is above M, not only is the righting lever non-existent, but it also becomes a capsizing moment. If the ship is then subjected to a light external force, it will incline sharply and, depending on the shape of the hull, may even capsize completely. In any case, a negative GM is a situation that must absolutely be avoided.

### What can cause an Abrupt shifting of G.

### Explain the effect a Suspended weight will have on stability.

### Explain Free surface effect.

### Explain Longitudinal stability.

### Explain Trim.

### Explain MCTC and MCTI.