Hull Identification Numbers (HIN)

Since about 1972 the US Coast Guard has been requiring that numbers be shown on the outside of boats built for sale in the USA. This applies to boats imported for sale and boats built domestically. The hull numbers normally appear on the transom and normally in the corner of the transom near where the deck, hull topsides and transom come together on the starboard side. The hull number may refer to an importer, sometimes a marketing company only, or a manufacturer. The number on most used boats consists of 12 characters, the first three represent a code for the importer/builder. Depending on the boat, these three little characters (most commonly about 1/2" high) may be the only clue on the outside of the boat that gives information about its place of origin. We have in our office a list of 3-character prefixes and the companies/persons to whom they were assigned. There are over 10,000 records in this list, so it is a good-sized list.

Since about 1996, hull identification numbers issued by builders that export boats to Europe have included a two-character prefix that will precede the 12 character number and be separated from it by a hyphen. The two character prefix will indicate the country of origin of the boat; US for the United States.

By the way, the last 9 characters of the HIN have a meaning as well. Three formats for these exist as far as we know:

• characters 4-8 inclusive are sequence numbers/model numbers assigned by the builder/importer (they do not have to start with 00001 for hull number 1). Some have used character 4 or characters 4 and 5 as model designations with the remaining characters in this segment being a sequence number. Some builders do not number boats in sequence, however, many do.
• characters 9-12 are the ones that have several official styles, but they all include information about when the boat was built/imported.
  • Style 1 - character 9 is usually an M, the next two characters are the year of the "date of manufacture" (for example "79" is the 1979 model year, which by common acceptable practice ran from Aug through July) and the last character is the month of the "date of manufacture". The month is designated by letter. The months start with Aug of the year prior to the year indicated in the previous 2 characters of the HIN. So that A is for Aug, B is for Sept, C is for Oct, etc. There are L months in a year (L is July). For example "M79B" means the date reference is Sept of 1978; and "M79G" means the date reference is Feb of 1979. This style was used in the period 1972 through 1983, and perhaps into 1984.
  • Style 2 - has the month and year in a more normal display for the "date of manufacture". Characters 9 and 10 are the month number (01 is Jan, 02 is Feb, 10 is Oct, etc) and the last two characters are the year. This style was used concurrently with style 1.
  • Style 3 - has a "model year" most visible (i.e. they are the last two characters), but the month and year of "date of manufacture" less visible. This style was optional during most of 1984, but became mandatory about Aug. 1, 1984 and is still in use. In this style, the ninth character is a letter for the month of the "date of manufacture". A is for Jan, B is for Feb, C is for Mar, etc. The tenth character is the last digit of the year of the "date of manufacture". The last two characters are the model year designated by the builder. The model year is indicated with the last two digits of the year (e.g. year 1990 would be 90).

Using the model year as an indication of boat age (as measured by the time that has passed since it was built) could lead one to believe that the boat is maybe a year (or more?) newer than the boat really is. The current definition for the "date of manufacture" is supposed to be a date that falls within the span of time between the commencement of construction and the time the boat leaves the place of manufacture. Thus, as we read the rules, it is possible to have a boat that was started in 1995, completed in 1997 but not shipped until 1999 with a "date of manufacture" portion of the HIN indicating the year of manufacture as 1999. In the case of imported boats, the "date of manufacture" is supposed to be the date of importation. Again, any year of actual construction seems permissible for the imported boat. Since it is generally conceded that the newer boat is worth more than an older boat, one can probably safely assume that the rules will be applied by the sellers so as to indicate that the boat to which the hull number is affixed appears as new as possible.

For practical purposes the "model year" as indicated in the HIN is usually either the same as the year in the "date of manufacture" or the year following that. Here again, later is probably more desirable for the builder/importer rather than earlier, so ... Using the example of the foregoing paragraph, the boat whose construction was actually completed in 1997 but not shipped until 1999, might have a model year designation of 2000. For quite some time it was traditional for boat builders to consider the model year to begin in the month of Aug (so that model year 1974 actually began in Aug of 1973. We do not believe there is any requirement for that convention to be adopted by all builders/importers.

If you ever observe that the HIN has been modified on the boat in which you are interested, or you suspect that it has been, for reasons other than repair or painting or the like, you have every right to ask a few questions. It is illegal to change the HIN without permission. As indicated above, there is an economic motivation to changing the year numbers. And, when there is an economic motivation, you can be sure that some will exploit it. Be observant, but not paranoid, when buying a boat. Hull number modifications are rare in our experience. Check the number, see if it has been altered (it should normally be molded into the gel coat on a fiberglass boat), Compare it with what you have been told and proceed accordingly.

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