In
solid mechanics
Solid mechanics, also known as mechanics of solids, is the branch of continuum mechanics that studies the behavior of solid materials, especially their motion and deformation under the action of forces, temperature changes, phase changes, and ...
,
structural engineering
Structural engineering is a sub-discipline of civil engineering in which structural engineers are trained to design the 'bones and muscles' that create the form and shape of man-made structures. Structural engineers also must understand and cal ...
, and
shipbuilding
Shipbuilding is the construction of ships and other floating vessels. It normally takes place in a specialized facility known as a shipyard. Shipbuilders, also called shipwrights, follow a specialized occupation that traces its roots to bef ...
, hogging and sagging describe the shape that a
beam or similar long object will
deform into when
loading is applied. ''Hogging'' describes a beam that curves upwards in the middle, and ''sagging'' describes a beam that curves downwards.
Ships
Dynamic stress
Hogging is the stress a ship's
hull
Hull may refer to:
Structures
* Chassis, of an armored fighting vehicle
* Fuselage, of an aircraft
* Hull (botany), the outer covering of seeds
* Hull (watercraft), the body or frame of a ship
* Submarine hull
Mathematics
* Affine hull, in affi ...
or
keel
The keel is the bottom-most longitudinal structural element on a vessel. On some sailboats, it may have a hydrodynamic and counterbalancing purpose, as well. As the laying down of the keel is the initial step in the construction of a ship, in Br ...
experiences that causes the center or the keel to bend upward. Sagging is the stress a ship's hull or keel is placed under when a wave is the same length as the ship and the ship is in the trough of two waves. This causes the middle of the ship to bend down slightly, and depending on the level of bend, may cause the hull to snap or crack.
Sagging or dynamic hogging may have been what sank the ''
Prestige
Prestige refers to a good reputation or high esteem; in earlier usage, ''prestige'' meant "showiness". (19th c.)
Prestige may also refer to:
Arts, entertainment and media Films
* ''Prestige'' (film), a 1932 American film directed by Tay Garnet ...
'' off Spain on 19 November 2002.
The 2013 loss of container ship ''
MOL Comfort'' off the coast of
Yemen
Yemen (; ar, ٱلْيَمَن, al-Yaman), officially the Republic of Yemen,, ) is a country in Western Asia. It is situated on the southern end of the Arabian Peninsula, and borders Saudi Arabia to the north and Oman to the northeast and ...
was attributed to hogging. Subsequent lawsuits blamed the shipbuilder for design flaws.
Time-induced stress
Hogging, or "hog", also refers to the semi-permanent bend in the keel, especially in wooden-hulled ships, caused over time by the ship's center's being more buoyant than the bow or stern. At the beginning of her 1992 refit, had over 13 inches (33 cm) of hog. The keel blocks in the
drydock were set up especially to support this curve. During her three years in drydock, the center keel blocks were gradually shortened, allowing the hog to settle out. Additionally, the diagonal riders specified in her original design to resist hogging, which had been removed in an earlier refit, were restored. The similar-sized had 36 inches (91 cm) of hog before refitting in the mid-1990s.
Cargo loading
During loading and discharging cargo, ships bend (hog or sag) due to the distribution of the weights in the various holds and tanks on board.
The maximum amount of cargo that a vessel can load often depends on whether her
Plimsoll mark is submerged or not. Therefore, sagging can reduce her effective cargo capacity – especially if her
loadline has already been reached prematurely due to the sag. This is taken into account when calculating
cargo
Cargo consists of bulk goods conveyed by water, air, or land. In economics, freight is cargo that is transported at a freight rate for commercial gain. ''Cargo'' was originally a shipload but now covers all types of freight, including tra ...
, by applying what is called a "3/4 mean draft". This method is also called the "two-thirds mean correction", directly derived from
Simpson's first rule.
Structural beams
In building construction, the sagging of beams is called "
deflection
Deflection or deflexion may refer to:
Board games
* Deflection (chess), a tactic that forces an opposing chess piece to leave a square
* Khet (game), formerly ''Deflexion'', an Egyptian-themed chess-like game using lasers
Mechanics
* Deflection ...
". The amount of deflection varies, based on the beam's stiffness, the span between supports, and the load it carries. Sagging is a common problem in older houses.
See also
*
Glossary of nautical terms
*
Strength of ships
The strength of ships is a topic of key interest to naval architects and shipbuilders. Ships which are built too strong are heavy, slow, and cost extra money to build and operate since they weigh more, whilst ships which are built too weakly suffe ...
*
Hog chains
Hog may refer to:
Animals
* Pig
** Usually referring to the domestic pig
** Sometimes referring to other animals in the family Suidae, including:
*** Warthog
*** Red river hog
*** Giant forest hog
* groundhog
* hedgehog
* hog (sheep), a yearling ...
References
*
External links
''Constellations 1994 restoration articlehas several photos showing the hogging.
{{DEFAULTSORT:Hogging And Sagging
Structural analysis
Nautical terminology