Naval architecture

Naval architects design safe, useful or beautiful ships and boats for their clients. For details of construction techniques see shipbuilding and boat building.

Safety

Maritime safety is concerned with four major items. The strength of the hull and superstructure, the instantaneous stability, ultimate stability, and equipment for safety and navigation.

Related Topics:
Hull - Instantaneous stability - Ultimate stability - Navigation

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Strength is an issue because most ships can be twisted or suspended between two wave-tops under some conditions. The hull only has to fracture once to fail in service and endanger people. Hulls are customarily overdesigned by a factor of 5 to 7 for the expected stresses, and some ships are overdesigned to 10 or more for extreme service.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Instantaneous stability is a measure of how the vessel's buoyancy is distributed. For example, a flat wooden board floats flat on water because its buoyancy is widely distributed. Some useful measures are the angles of roll (tilting to the side) or pitch (nose down or up) per unit of windspeed, or ton of misplaced cargo.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Ultimate stability is concerned with where the vessel's center of gravity has been located. It measures the angles of pitch or roll at which the vessel capsizes and cannot recover. Sometimes this is more than 180 degrees; for example, most lifeboats and singled-hulled pleasure sailboats can recover after being dropped into a basin upside down. Most vessels can recover from rolls of 100 degrees (a knockdown), and pitches of 30 degrees. Larger ships can be overstressed by their own weight at extreme pitches.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

In all designs, calculations are performed with cargo and fuel present and absent. Cargo and fuel can act as a ballast, holding the bottom of the ship down. If absent, or placed above waterline, the ship may become topheavy. Ultimate stability calculations have to plan what will happen if the cargo or fuel shifts- or specify that this must never occur.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Safety equipment includes not just lifeboats and lifejackets. It also includes navigational and signalling equipment.

Related Topics:
Lifeboat - Lifejacket

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

To avoid collisions, vessels mount navigation lights that permit other vessels to determine the type and relative angle of a vessel. This is to decide if there's a danger of collision. For example, almost all vessels mount a green light on the right, a red light on the left, and a white light in back. If you can see both the green and red light, danger of a collision exists. Large "steamers" must mount red lights on major masts. Ships at anchor hoist a single bright white light (the anchor light).

Related Topics:
Collision - Navigation light

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Modern navigational equipment also include GPS, to locate one's position in the trackless ocean. To navigate tight passages in fog or darkness, and avoid other vessels, radar is useful. To avoid shallows and reefs, sonar is also useful.

Related Topics:
GPS - Fog - Radar - Shallow - Reef - Sonar

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

As a practical matter, celestial navigation, in which a vessel measures the angles of sun, moon and stars against a clock, is now rarely practiced. It is, however, widely learned, and treasured.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~