mass is referred to as hydrodynamic added mass. In ship design, the energy required to accelerate the added mass must be taken into account when performing a sea keeping analysis. For ships, the added mass can easily reach one fourth or one third of the mass of the ship and therefore represents a significant inertia, in addition to frictional and wavemaking drag forces. For certain geometries freely sinking through a column of water, hydrodynamic added mass associated with the sinking body can be much larger than the mass of the object. This situation can occur, for instance, when the sinking body has a large flat surface with its normal vector pointed in the direction of motion (downward). A substantial amount of kinetic energy is released when such an object is abruptly decelerated (e.g., due to an impact with the seabed). In the offshore industry hydrodynamic added mass of different geometries are the subject of considerable investigation. These studies typically are required as input to subsea dropped object risk assessments (studies focused on quantifying risk of dropped object impacts to subsea infrastructure). As hydrodynamic added mass can make up a significant proportion of a sinking object's total mass at the instant of impact, it significantly influences the design resistance considered for subsea protection structures. Proximity to a boundary (or another object) can influence the quantity of hydrodynamic added mass. This means that added mass depends on both the object geometry and its proximity to a boundary. For floating bodies (e.g., ships/vessels) this means that the response of the floating body (i.e., due to wave action) is altered in finite water depths (the effect is virtually nonexistent in deep water). The specific depth (or proximity to a boundary) at which the hydrodynamic added mass is affected depends on the body's geometry and location and shape of a boundary (e.g., a dock, seawall, bulkhead, or the seabed). The hydrodynamic added mass associated with a freely sinking object near a boundary is similar to that of a floating body. In general, hydrodynamic added mass increases as the distance between a boundary and a body decreases. This characteristic is important when planning subsea installations or predicting the motion of a floating body in shallow water conditions. Aeronautics In aircraft (other than lighter-than-air balloons and blimps), the added mass is not usually taken into account because the density of the air is so small. See also