Hogging
Hogging is a structural deformation that bends the hull upward at midships. It’s the opposite of sagging, and it happens when most of the weight sits toward the bow and stern instead of the center. Ships also tend to hog in light condition, where the midship area is less supported by cargo weight. The effect looks similar to a beam supported in the middle with weights placed at both ends.
In a survey, hogging shows up when the midships draft is smaller than the mean of the forward and aft drafts. This difference indicates that the hull is flexed upward. Because hogging reduces the underwater volume, it also reduces the vessel’s displacement. Ignoring this leads to overstated cargo figures.
To correct for this, surveyors rely on a representative mean draft. For most ships, the three-quarter mean draft is used because it gives more weight to the midships reading. Some large bulk carriers, especially Cape Size vessels, may have dedicated deflection correction tables. These are important because heavy ballast in a central hold can cause a double hog, which exaggerates the error. In these cases, a small reduction in the midships draft, such as three to six centimetres, may be required based on class guidance.
