When should we use p = ρ.g.h and p = ρ.g.hcg for hydrostatic pressure?

[wmsaqqa]

For the hydrostatic pressure, when do we use [ p = ρ.g.h ] and [ p = ρ.g.hcg ]

where:
ρ = density
g = acc of gravity
h = height of water column
hcg = the distance to the center of gravity from the surface of water downward

 

[SteamKing]

It depends. h should actually be measured from the surface to the 'center of pressure', which is not always located at the c.g. of a submerged body.

http://www.nptel.iitm.ac.in/courses/Webcourse-contents/IIT-KANPUR/FLUID-MECHANICS/lecture-5/5-2_hydro_thrust_plane_surf.htm