Freeboard. The freeboard of a ship at any time is the vertical distance between the upper edge of the deck line and the water line. Statutory Freeboard. Statutory freeboard is the vertical distance between the upper edge of the deck line and the upper edges of the respective loadlines.
Because of the different densities of fresh and salt water, the displacement of a vessel and hence her draught will change from one area to another. The density of fresh water is 1 tonne/cubic metre and is used as the basis against which the relative densities of other substances are measured, ie salt water has…
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 cargo capacity. The structure of…
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 lowered too much this can…
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 depend on the fore and…
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 quickly from a roll and…
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 internal volume of a ship…
Other electronic navigation systems employed in the past include Consol, Loran and Omega (similar to Decca) and the forerunner to GPS, the American Transit system. The latter consisted of 5ive low orbit (1100 kms) satellites orbiting the earth in approximately one and three quarter hours. The system made use of the Doppler effect, ie changes…
Another system which operated along the South African and Namibian coast was a series of Radio Transponder Beacons. There were five on the Namibian coast and fifteen on the South African coast. The beacons operated in the 10 GHz (10cm) and 3 GHz (10 cm) radar bands. The beacons would emit a characteristic signal when…
One of the systems which were used along the Namibian and South African coasts was a series of marine radio beacons situated along the coastline and which provided vessels navigating in our waters with a means of obtaining radio bearings. Six of these stations were situated in Namibia and twenty four in South Africa. The…
