The hydrostatic force acting on a tank is
 | (3–28) |
where ρt is the liquid density and g is the gravitational acceleration.
The hydrostatic moment acting on the tank about the LTA origin is
 | (3–29) |
Employing Equation 3–27 the general form of the hydrostatic force and moment with respect to the LSA origin is
 | (3–30) |
where 
is of the 6x1 matrix form containing the force and moment components given by
Equation 3–28 and Equation 3–29.
When a structure with internal tanks freely floats in still water, at its equilibrium position the following conditions are satisfied:
 | (3–31) |
where ρ is the water density, 
is the volume of the
displacement of external water (see Equation 3–1), and 
is the center of buoyancy in FRA.