How to Read and Check a Hull Identification Number (HIN)

What the 12 characters mean

The format is set by federal rule, 33 CFR 181.25. A HIN is exactly twelve characters with no slashes, hyphens or spaces, and each position has a job:

• Characters 1 to 3: the manufacturer identification code (MIC), assigned by the Coast Guard to the builder or, for foreign-built boats, to the U.S. importer.
• Characters 4 to 8: the builder's serial number. Letters and numbers are both allowed, except the letters I, O and Q.
• Character 9: a letter for the month, A for January through L for December.
• Character 10: the last digit of the year the boat was built, or certified when a certification date is required.
• Characters 11 and 12: the last two digits of the model year.

Take a made-up example, XYZ12345F526. XYZ is the builder code, 12345 is the hull's serial, F5 means June of a year ending in 5, and 26 is the model year. So it was built in June 2025 and sold as a 2026 model. The build date can fall anywhere from the start of construction to when the boat left the plant, so a build date months ahead of the model year is normal.

You may see "US-" in front of the number. That is the country of origin code and is allowed. Any other text printed within two inches of the HIN has to be boxed off or put on a separate label so nobody mistakes it for part of the number.

Where to find it on the boat

Under 33 CFR 181.29 every hull carries two identical HINs. The primary one goes on the starboard outboard side of the transom, within two inches of the top of the transom, gunwale or hull-to-deck joint, whichever is lowest. Boats without a usable transom carry it on the starboard side of the hull within a foot of the stern. On pontoon boats and catamarans with replaceable hulls it goes on the aft crossbeam within a foot of the starboard hull. If rails or fittings would block it, the builder puts it as close to that spot as it can.

The second HIN is hidden somewhere inside the boat or under a piece of hardware. Both numbers have to be carved, burned, stamped, embossed, molded or bonded on so that changing or removing them would be obvious, in characters at least a quarter inch high. If the number is on a plate, removing that plate should normally scar the hull around it, and the HIN cannot sit on a removable part.

Running a boat HIN lookup

The free tools below come from the Coast Guard, and each answers a narrower question than you might hope.

The MIC search. The Coast Guard's Manufacturers Identification page lets you search by company name or MIC, and it listed 16,263 records when we checked. Type in the first three characters and you get the company and address on file. Today, SER comes back as Sea Ray Boats in Knoxville, Tennessee. The code is registered to whoever applied for it, so the name may be a corporate owner rather than the brand on the hull. Several recent recalls list BLB under Brunswick Family Boat Co. When the code returns a builder that has nothing to do with the boat in front of you, stop and ask why. Shopping for a used Sea Ray or a Bayliner? Run the code before you go see the boat.

The recall search. The Coast Guard recall database can be searched by MIC, company or recall number, then narrowed by model and model year. The builder code and model year are both right there in the HIN.

PSIX. The Coast Guard's Port State Information Exchange has a HIN field on its vessel search. Its data is a weekly snapshot covering U.S. flag vessels and foreign vessels in U.S. waters, and the Coast Guard does not vouch for its accuracy or completeness. A hit is a lead, not proof. If the boat is documented, see our guide to documented vs state titled boats.

None of these tools shows a state title or lien. For that you need the title itself and the agency that issued it, which our boat title transfer guide walks through.

Red flags when you check a HIN

Read the transom in good light, photograph it, and hold the title next to it. Slow down if you see any of these:

• The number on the transom does not match the title or registration, even by one character. The Coast Guard's own guidance says a single wrong character changes the boat's identity.
• Anything other than twelve characters on a modern boat, an I, O or Q in the serial, or a month letter past L.
• A model year in characters 11 and 12 that disagrees with the year on the title or the listing.
• Fresh gelcoat, grinding marks, a new-looking plate or screws that could come out cleanly where the HIN should be.
• A builder code that comes back to the wrong company in the MIC search.

Federal law takes this seriously. Under 33 CFR 181.35 no one may remove or alter a HIN unless the Coast Guard authorizes it. A transom that has been worked over is a reason to walk away. This check belongs on any used boat inspection, and it applies to a used Tracker aluminum fishing boat just as much as a fiberglass bowrider.

What states do with a bad or missing HIN

States check HINs too. Under 33 CFR 174.16, since January 1, 2017, a state issuing authority has to confirm that a boat built or imported on or after November 1, 1972 has a compliant primary HIN before it issues, renews or updates ownership on a registration. If the boat does not have one, the state assigns a HIN and confirms the owner has permanently fixed it to the hull.

The Coast Guard's 2020 policy memo lets states verify a HIN by pencil tracing, photos, inspection, owner affidavit, contacting the builder, the MIC list or the National Insurance Crime Bureau database. If the HIN is invalid and the boat is under ten years old with its builder still in business, the state asks the Coast Guard to have the builder correct it. Otherwise the state issues its own HIN in the current format.

Florida shows how that looks in practice. FLHSMV's procedure calls a Florida-assigned HIN an FLZ number, and the state assigns HINs to homemade boats, to boats without a manufacturer HIN or with one that is not properly formatted, and to boats coming off Coast Guard documentation onto a Florida title. A boat built before November 1, 1972 does not need a 12-character HIN there. So an FLZ number on an older boat is not a red flag on its own, but the title should explain it. And if you build a boat for yourself, federal rules require you to get a HIN from your state's issuing authority and fix it to the hull.