46 CFR §170.290

1. (a)When doing the damage stability calculations required by this subchapter, the virtual increase in the vessel's vertical center of gravity due to liquids in tanks must be determined by calculating—
   1. (1)For each type of consumable liquid, the free surface effect of at least one transverse pair of wing tanks or a single centerline tank; and
   2. (2)The free surface effect of each partially filled tank containing other than consumable liquids.
2. (b)For the purpose of paragraph (a)(1) of this section, the tank or combination of tanks selected must be those having the greatest free surface effect.
3. (c)When doing the calculations in paragraph (a) of this section, the free surface effect of a liquid in a tank must be determined by—
   1. (1)Assuming the vessel is heeled five degrees from the vertical; or
   2. (2)Calculating the shift of the center of gravity of the liquid in the tank by the moment of transference method.