A ship structure is sufficiently strong if it can support all the fixed loads of its machinery, fittings and equipment, and all the cargo loads, and if it can withstand without permanent change of shape, cracking, and fracture all the hydrostatic and hydrodynamic loads which can be imposed upon it in calm water or in any kind of seaway in which it is supposed to operate.
Seafastening is the fastening of cargo while transportation at sea. When moving cargo by sea, it must be secured such that any movement which can damage cargo or ship must be avoided.