33 CFR § 181.25 - Hull identification number format.
Each of the hull identification numbers required by § 181.23 must consist of twelve characters, uninterrupted by slashes, hyphens, or spaces, as follows:
(b) Characters four through eight must be a serial number assigned by the manufacturer in letters of the English alphabet, or Arabic numerals, or both, except the letters I, O, and Q.
(c) Characters nine and ten must indicate the month and year of certification when a date of certification is required. In all other cases characters nine and ten must indicate the date of manufacture. The date indicated can be no earlier than the date construction or assembly began and no later than the date the boat leaves the place of manufacture or assembly or is imported into the United States for the purposes of sale. Character nine must be indicated using letters of the English alphabet. The first month of the year, January, must be designated by the letter “A”, the second month, February, by the letter “B”, and so on until the last month of the year, December. Character ten must be the last digit of the year of manufacture or certification and must be an Arabic numeral.
(d) Characters eleven and twelve must indicate the model year using Arabic numerals for the last two numbers of the model year such as “82” for 1982 and “83” for 1983.