13.0 Ship constructions and Naval architecture
13.1 Define Seaworthiness and Stability
Seaworthiness
Seaworthiness is the required degree of fitness and safety a vessel must possess at the commencement of its voyage, considering all probable circumstances.
A seaworthy ship is one that is fit for any normal perils of the sea, including the fitness of the vessel itself, as well as any equipment on it and the skills and health of its crew.
Stability
Stability can be defined as the property of a body that causes it, when disturbed from a condition of equilibrium or steady motion, to develop forces or moments that restore its original condition.
The term vessel stability implies the tendency of a floating vessel to return to its original upright position of equilibrium after being tipped by the forces of wind and sea.
13.1.1 Describe the Principles of Flotation, State the Archimedes’ Principle
Principle of flotation: A floating object displaces a weight of fluid equal to its own weight. Every ship, submarine, and dirigible must be designed to displace a weight of fluid at least equal to its own weight.
Archimedes' principle indicates that the upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially submerged, is equal to the weight of the fluid that the body displaces.
In a completely submerged object, the volume of displaced fluid equals the volume of the object. If the object is floating, the volume of the displaced fluid is less than the volume of the object, but the buoyant force is equal to the weight of the object.
Buoyant force = density of fluid × volume of displaced fluid × acceleration due to gravity.
13.1.1.1 Displacement
Displacement is the weight of water that a ship displaces when it is floating, which in turn is the weight of a ship and its contents.
13.1.1.2 Buoyancy
Buoyant force is the force that a fluid exerts on an object that is immersed within it. It is called buoyant force, because this force is a lifting force, often making the object buoyant. Buoyant force can be calculated using Archimedes' Principle.
