Springing
Encyclopedia
Springing as a nautical term refers to global vertical resonant hull girder vibration due to oscillating wave loads along the hull
of the ship.
The hydrodynamic theory
of springing is not yet fully understood due to the complex description of the surface waves and structure interaction. It is, however, well known that larger ships with longer resonant periods are more exposed to this type of vibration. Examples of this include very large crude
carriers and bulk carriers, but possibly also container vessels. The container ships are more slender, has higher service speeds and have more pronounced bow flare. These are also known to get significant whipping (transient) vibrations from bow impacts. Whipping may also occur on blunt ships especially in the cases of flat bottom impacts in the bow area. The bottom part of the bow however rarely exits from the water on such ships.
In the extreme cases it may cause severe fatigue cracking of critical structural details, especially in moderate to rough head seas with low peak periods. Vibration in ballast condition is normally more easily excited by waves than cargo condition. The trade may also matter, since some ships experience more head wind and waves in ballast conditions, while other ships may experience more head wind and waves in cargo condition, thereby vibrating less overall.
The first experience with this phenomenon is related to fatigue cracking on Great Lakes
bulk carrier
s (700 feet) during the 1950s. Later 1000 feet Great Lakes bulk carriers experienced the same problems even if the strength requirements became stricter. Ocean
-going ships have not had this problem until recently, when high tensile steel was introduced as a common material in the whole ship to reduce the initial costs. This makes the ships less stiff and the nominal stress level higher.
Today's ship rules does not account for this effect which may dominate the contribution to fatigue for some vessels. The vibration from whipping may also increase the extreme loading of ships potentially contributing to breaking vessels in two in harsh storms.
Hull (watercraft)
A hull is the watertight body of a ship or boat. Above the hull is the superstructure and/or deckhouse, where present. The line where the hull meets the water surface is called the waterline.The structure of the hull varies depending on the vessel type...
of the ship.
The hydrodynamic theory
Fluid dynamics
In physics, fluid dynamics is a sub-discipline of fluid mechanics that deals with fluid flow—the natural science of fluids in motion. It has several subdisciplines itself, including aerodynamics and hydrodynamics...
of springing is not yet fully understood due to the complex description of the surface waves and structure interaction. It is, however, well known that larger ships with longer resonant periods are more exposed to this type of vibration. Examples of this include very large crude
Petroleum
Petroleum or crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid organic compounds, that are found in geologic formations beneath the Earth's surface. Petroleum is recovered mostly through oil drilling...
carriers and bulk carriers, but possibly also container vessels. The container ships are more slender, has higher service speeds and have more pronounced bow flare. These are also known to get significant whipping (transient) vibrations from bow impacts. Whipping may also occur on blunt ships especially in the cases of flat bottom impacts in the bow area. The bottom part of the bow however rarely exits from the water on such ships.
In the extreme cases it may cause severe fatigue cracking of critical structural details, especially in moderate to rough head seas with low peak periods. Vibration in ballast condition is normally more easily excited by waves than cargo condition. The trade may also matter, since some ships experience more head wind and waves in ballast conditions, while other ships may experience more head wind and waves in cargo condition, thereby vibrating less overall.
The first experience with this phenomenon is related to fatigue cracking on Great Lakes
Great Lakes
The Great Lakes are a collection of freshwater lakes located in northeastern North America, on the Canada – United States border. Consisting of Lakes Superior, Michigan, Huron, Erie, and Ontario, they form the largest group of freshwater lakes on Earth by total surface, coming in second by volume...
bulk carrier
Bulk carrier
A bulk carrier, bulk freighter, or bulker is a merchant ship specially designed to transport unpackaged bulk cargo, such as grains, coal, ore, and cement in its cargo holds. Since the first specialized bulk carrier was built in 1852, economic forces have fueled the development of these ships,...
s (700 feet) during the 1950s. Later 1000 feet Great Lakes bulk carriers experienced the same problems even if the strength requirements became stricter. Ocean
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
-going ships have not had this problem until recently, when high tensile steel was introduced as a common material in the whole ship to reduce the initial costs. This makes the ships less stiff and the nominal stress level higher.
Today's ship rules does not account for this effect which may dominate the contribution to fatigue for some vessels. The vibration from whipping may also increase the extreme loading of ships potentially contributing to breaking vessels in two in harsh storms.