(a) Each number required by § 173.15 must:
(1) Be painted on or permanently attached to each side of the forward half of the vessel except as allowed by paragraph (b) or required by paragraph (c) of this section;
(2) Be in plain vertical block characters of not less than 3 inches in height;
(3) Contrast with the color of the background and be distinctly visible and legible;
(4) Have spaces or hyphens that are equal to the width of a letter other than “I” or a number other than “1” between the letter and number groupings (Example: DC 5678 EF or DC-5678-EF); and
(5) Read from left to right.
(b) When a vessel is used by a manufacturer or by a dealer for testing or demonstrating, the number may be painted on or attached to removable plates that are temporarily but firmly attached to each side of the forward half of the vessel.
(c) On vessels so configured that a number on the hull or superstructure would not be easily visible, the number must be painted on or attached to a backing plate that is attached to the forward half of the vessel so that the number is visible from each side of the vessel.
(d) Each number displayed on a tender exempted under § 173.13 must meet the requirements of paragraph (a) of this section and have a space or hyphen that is equal to the width of a letter other than “I” or a number other than “1” between the suffix and the number. (Example: DC 5678 EF 1 or DC-5678-EF-1.)