Coefficients of Fineness

A table of offsets, although accurately defining the hull shape, does not provide an immediate feel of the main characteristics of that shape. There are some “coefficients” which can be obtained for the underwater hull which provide clues as to its general nature and its likely behaviour.

BUOYANCY AND DISPLACEMENT

It was Archimedes who first realised, in his “eureka” moment, that a body that is immersed completely in water will displace a volume of water equal to the volume of the body and that the apparent weight of the body, when immersed, will be reduced by the weight of water displaced.

Lashing of containers on deck

In the early years of containerisation, existing general cargo vessels were converted with the removal of ‘tween decks and the addition of cell guides into the cargo holds. On deck, the hatchcovers were strengthened and fittings added for lashings.

THE METACENTRIC DIAGRAM

When a ship is heeled through a small angle, the centre of buoyancy moves to a new position B1 and the buoyancy force acts through a point M on the centreline. M is known as the transverse metacentre.

DEFINING THE SHIP GEOMETRY

As with any engineering product, precision is necessary in defining the geometry of a ship. Again, in common with most disciplines, an internationally recognised terminology has grown up over the years to aid this definition.