46 CFR 131.220 - Drafts.
(a) Each vessel must have the drafts of the vessel plainly and legibly marked upon the stem and upon the sternpost or rudderpost, or at any place at the stern of the vessel that may be necessary for easy observance. The bottom of each mark must indicate the draft.
(b) Each draft must be taken from the bottom of the keel to the surface of the water at the location of the marks.
(c) When, because of raked stem or cutaway skeg, the keel does not extend forward or aft to the draft markings, the datum line from which the draft is taken must be the line of the bottom of the keel projected forward or aft, as the case may be, to where the line meets that of the draft markings projected downward.
(d) When a skeg or other appendage extends below the line of the keel, the draft at the end of the vessel adjacent to that appendage must be measured to a line tangent to the lowest part of the appendage and parallel to the line of the bottom of the keel.
(e) Drafts must be separated so that the projections of the marks onto a vertical plane are of uniform height, equal to the vertical spacing between consecutive marks.
(f) Marks must be painted in a color contrasting with that of the hull.
(g) Where marks are obscured because of operational constraints or by protrusions, the vessel must be fitted with a reliable draft-indicating system from which the drafts at bow and stern can be determined.