Grade 12 – Nautical Science

September 23, 2020

Stability of vessels – concepts and definitions

The following concepts and definitions apply to the stability of vessels at sea: Tonnage deck. This is the upper deck in single deck ships and the deck next below the upper deck in other ships. Tonnage. This is the enclosed/internal capacity (volume) of a ship measured in tons, i.e. the […]
September 23, 2020

States of stability

Stable equilibrium. The forces of gravity (G) and the buoyancy (B) must be in line and the centre of gravity (G) must be below the metacentre (M). Whilst this is the state a vessel should be in, if the centre of gravity is too low, the ship will recover too […]
September 23, 2020

Trim

As stated on the concepts and definitions page, trim is the inclination of the ship’s designed horizontal fore and aft plane with the surface of the water in which she floats. When in normal trim this plane lies parallel with the surface of the water. The condition of trim will […]
September 23, 2020

Effect of the movement of cargo/ballast/personnel

By shifting cargo/ballast/personnel about the vessel, the stability of the vessel can be altered advantageously or adversely. By shifting weight from higher up in a ship to a lower position, one would be lowering the centre of gravity and therefore increasing the stability. However, if the centre of gravity is […]
September 23, 2020

Hull stresses

A ship is subjected to stresses from a complex system of forces and the structure must be braced and supported to withstand any reasonable combinations of load at a given time. The cost and weight in the construction of a ship must be balanced against strength, rigidity, sea worthiness and […]