What is hogging and sagging of ships?

 Hogging

    Longitudinal bending stress would occur if the ship were subjected to local loading at the fore end and after ends, (e.g. ship with machinery aft and in light condition with ballasted fore peak tank) the hull would tend to ‘hog.’

     This effect would be made worse if the wave crest were amidships with wavelength similar to ship length as shown.

Sagging

     If the load and the buoyancy distribution tended to distort the hull as shown (e.g.,. could be a ship with machinery amidships in light condition), is termed as sagging. This is made worse when the wave crests are at the ends of the ship, with a wavelength similar to ship length.