No Certificate of Documentation issued under this part will be deemed valid for operation of the vessel until the vessel is marked in accordance with this subpart.

The official number of the vessel, preceded by the abbreviation “NO.” must be marked in block-type Arabic numerals not less than three inches in height on some clearly visible interior structural part of the hull. The number must be permanently affixed to the vessel so that alteration, removal, or replacement would be obvious. If the official number is on a separate plate, the plate must be fastened in such a manner that its removal would normally cause some scarring of or damage to the surrounding hull area.

(a) For vessels other than those covered in paragraphs (b) and (c) of this section, the name of the vessel must be marked on some clearly visible exterior part of the port and starboard bow and the stern of the vessel. The hailing port of the vessel must be marked on some clearly visible exterior part of the stern of the vessel.

(b) Vessels with square bow. For vessels having a square bow, the name of the vessel must be marked on some clearly visible exterior part of the bow in a manner to avoid obliteration. The name and hailing port must be marked on some clearly visible exterior part of the stern.

(c) Recreational vessels. For vessels documented exclusively for recreation, the name and hailing port must be marked together on some clearly visible exterior part of the hull.

(d) The markings required by paragraphs (a), (b), and (c) of this section, which may be made by the use of any means and materials which result in durable markings, must be made in clearly legible letters of the Latin alphabet or Arabic or Roman numerals not less than four inches in height.

The OCMI for the zone in which the vessel is principally operated has final authority in any disputes concerning the permanence, durability, legibility, or placement of a vessel's markings.