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{{Short description|Shapes a beam deforms into when loads are applied}}In solid mechanics, structural engineering, and shipbuilding, 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 or keel 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 off Spain on 19 November 2002.The 2013 loss of container ship MOL Comfort off the coast of Yemen was attributed to hogging. Subsequent lawsuits blamed the shipbuilder for design flaws.NEWS,weblink Mitsubishi Heavy sued for ¥60 bil. over sunken freighter, The Japan News, The Yomiuri Shimbun, Jiji Press, 7 December 2014, 6 December 2014, dead,weblink" title="web.archive.org/web/20141210003543weblink">weblink 10 December 2014,

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, {{USS|Constitution}} had over 13 inches (33 cm) of hog.WEB, Otton, Patrick, 11 August 1997,weblink USS Constitution Rehabilitation And Restoration, 2 July 2006, 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 {{USS|Constellation|1854|6}} had 36 inches (91 cm) of hog before refitting in the mid-1990s.WEB,weblink The Constellation Restoration Effort - After Two Years, Louis F., Linden, 14 July 1997, Constellation Foundation, Inc., San Francisco Maritime National Park Association, 18 February 2020, WEB,weblink Constellation, Dictionary of American Naval Fighting Ships, 9 February 2004, Naval Historical Center, Washington Navy Yard, Department of the Navy, 2 July 2006, dead,weblink" title="web.archive.org/web/20060815012851weblink">weblink 15 August 2006,

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.{{citation|title=Measurement of bulk cargoes| work = Carefully to Carry | date =May 2008|publisher=UK P&I Club |page=8 |url=http://www.ukpandi.com/fileadmin/uploads/uk-pi/LP%20Documents/Carefully_to_Carry/Measurement%20of%20bulk%20cargoes%20-%20draught%20surveys.pdf | url-status = dead | archive-url =weblink" title="web.archive.org/web/20120324051805weblink">weblink | archive-date = 24 March 2012}} This is taken into account when calculating cargo, 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". The amount of deflection varies in accordance with the beam's stiffness, the span between supports, and the load it carries.WEB,weblink Design > Code Requirements > What is Allowable Deflection ?, Trus Joist, Weyerhaeuser Company, 14 February 2020, Sagging is a common problem in older houses.{{citation | url =weblink | title = How to Fix Sagging Floors: Understanding the common structural shortcomings that cause floors to sag and what to do about them | first = Steve | last = Jordan | date = 14 May 2019 | work = Old House Online | publisher = Cruz Bay Publishing, Inc. | access-date = 14 February 2020}}

See also

• Glossary of nautical terms
• Strength of ships
• Hog chains

References

• {{DANFS}}

External links

• Constellation's 1994 restoration article has several photos showing the hogging.
• weblink" title="web.archive.org/web/20081012172334weblink">Diagram showing hogging stress and the diagonal risers.