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 the length of 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.
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, 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==