Everything You Never Wanted to Know About Hull Identification Numbers (HINs)

A Hull Identification Number (HIN) is an identifier meant to uniquely identify a particular vessel. They are the equivalent of a Vehicle Identification Number (VIN) on a car. No two vessels should have the same HIN. The HIN is filed with many different documenting agencies, including states, the U.S. Coast Guard (USCG) (or other countries' coast guard), insurance companies, banks, marinas, etc. So just as listing a wrong Social Security Number on a tax return is likely to cause problems, listing a wrong HIN on a form is likely to cause problems too.

We have owned two boats. When we acquired them, the paperwork on both of them had a HIN listed that was different than was etched on the boat. Based on a sample size of two, this is a very common thing. If it is messed up, it is worth the trouble to get it fixed. (One had a misreading of the badly etched HIN, the other had the wrong build month recorded.)

A couple of caveats in the discussion below...This discussion is about recreational boats built since November 1, 1972 sold in the U.S. I'm not going to talk about boats built before 1972, homemade boats, boats imported from foreign countries that don't follow United States rules, or commercial boats.

The Manufacturer's Identification Code (MIC)

Each manufacturer of marine equipment, including boats, is assigned a three letter code that uniquely identifies them called the Manufacturer's Identification Code (MIC). For example, Catalina Yachts is assigned CTY. You can find the definitive list at USCGBoating.org. These codes are used throughout the boating industry, so if, for example, you visit the Fisheries Supply web site, their product descriptions includes these MIC identifiers.

Finding the HIN for Your Boat

First, let's find out what the HIN is that is assigned to your boat. The HIN should be recorded in two places on the boat (however, the rules have changed over the years, so boats built before August 1, 1984 may not follow all of the rules). Here are the exact rules for where a HIN should be located from 33 CFR §181.29:

§ 181.29 Hull identification number display.

Two identical hull identification numbers are required to be displayed on each boat hull.

(a) The primary hull identification number must be affixed—

(1) On boats with transoms, to the starboard outboard side of the transom within two inches of the top of the transom, gunwale, or hull/deck joint, whichever is lowest.

(2) On boats without transoms or on boats on which it would be impractical to use the transom, to the starboard outboard side of the hull, aft, within one foot of the stern and within two inches of the top of the hull side, gunwale or hull/deck joint, whichever is lowest.

(3) On catamarans and pontoon boats which have readily replaceable hulls, to the aft crossbeam within one foot of the starboard hull attachment.

(4) If the hull identification number would not be visible, because of rails, fittings, or other accessories, the number must be affixed as near as possible to the location specified in paragraph (a) of this section.

(b) The duplicate hull identification number must be affixed in an unexposed location on the interior of the boat or beneath a fitting or item of hardware.

(c) Each hull identification number must be carved, burned, stamped, embossed, molded, bonded, or otherwise permanently affixed to the boat so that alteration, removal, or replacement would be obvious. If the 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 hull identification number must not be attached to parts of the boat that are removable.

(d) The characters of each hull identification number must be no less than one-fourth of an inch high.

On a Catalina 320, the primary HIN is affixed on the starboard side aft, just below the rubrail. On the Catalina 22, it is on the transom just below the rubrail. In both cases, it was scratched into the fiberglass with an etching tool. On the 22, it was difficult to read partly because the handwriting sucked. The second HIN on the 320 is on the starboard side under the V-berth on the bulkhead, but on other boat models will be in other places.

Furthermore, § 181.27 says that:

With the exception of the characters “US-”, which constitute the country of origin code for the United States, if information is displayed on the boat within 2 inches of the 12-character hull identification number (HIN), that information must be separated from the HIN by means of borders or must be on a separate label, so that it will not be interpreted as part of the hull identification number.

HIN Formats

Since November 1, 1972 there have been three HIN formats: The Current Format, which has been used since August 1, 1984 to the present. And two older formats used between November 1, 1972 and July 31, 1984: The Straight Year Format and the Model Year Format.

The Current Format is described in § 181.25:

§ 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:

(a) The first three characters must be a manufacturer identification code assigned under § 181.31(a) or the importer designation assigned under § 181.31(b).

(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.

So, for example, a Catalina 320 HIN begins with CTY. This is followed by a serial number begins with the letter "C", then followed by a four digit sequential hull number (very early 320s used Q instead of C, but Q is not allowed in the serial number as described in the rules above because it might be confused with 0). So hull #87, would be C0087. For the Catalina 22, the HIN serial number beings with the letter "H" followed by a four digit sequential hull number. However, Catalina has made more than 20000 Catalina 22s, so this has rolled over twice. If you see H2284 as the serial number, you will need to look to the last 4 characters to determine whether the hull number is 2284, 12284, or 22284 from the HIN and doing a little research on when these hull numbers rolled over. Only a few boat models have had more than 10000 hulls built and have this issue.

The month of manufacture is then encoded with a letter A-L. This followed by the last digit of the year of manufacture. So, October of 1993 would be encoded J3 (but so would October of 2003). The last two digits are the model year of the boat. Model years typically start at some point in the previous year. For the Catalina 320, the new model year starts in June of the previous year, but many manufacturers start their model year in August. Model year 1994 would be encoded as 94, whereas model year 2004 would be encoded 04.

So putting it all together, Catalina 320 hull #87 build in October of 1993 as a 1994 model year would have a HIN CTYC0087J394.

Note that HINs can contain the letter I in the MIC and in the month of manufacture, and that is a different character than the number 1. Make sure that I, 1, L, O, Q, and 0 are recorded correctly when submitting any paperwork.

The older formats are encoded like this:

Straight Year: 3 digit MIC, 5 digit serial #, 2 digit month of production, 2 digit year. Example: CYT6A130579 for Cobalt Yachts with serial number 6A130, built in May of 1979.

Model Year: 3 digit MIC, 5 digit serial #, the letter M, 2 digit model year, 1 letter month of production. The key for the month in Model Year format is A=August, B=September, ... L=July. Example: ZVMD1769M80L for Vandestadt and McGruer with serial number D1769, built in July of 1980. Boats built a month later would have the last four characters being M81A.

What To Do When the HIN is Wrong

When both of our boats had an improper HIN on some of the paperwork, we needed to get it fixed with the Coast Guard and the state. We first needed photographs and a rubbing of the HIN on the hull. Then we needed to present that info to the state department of licensing. For the Catalina 22, after paying appropriate fees, a new registration and title was issued. For the 320, the title company got the HIN straightened out with the Coast Guard documentation, and after presenting the Coast Guard documentation to the state, the state issued a new registration with the fixed HIN. The old HIN is recorded in a comment on the registration.

The Coast Guard rules for a malformed HIN are described in this document (along with much other materials about HINs). It shows this flow chart for how to fix a HIN: