Hull identification
What Is a Hull Identification Number? A Boat Owner's Guide
By The VesselBook Team · Published July 28, 2026 · 5 min read
A Hull Identification Number (HIN) is a 12-character code that permanently identifies a single boat hull, in the same way a VIN identifies a single car. In the United States, every boat built or imported since 1 November 1972 must carry one, and it must be permanently attached to the hull itself — not to a plate that can be swapped, and not to the engine or the trailer.
The HIN is the only part of a boat that never changes. Names change, registration numbers change, engines are replaced, owners come and go. The hull, and the number moulded or fixed to it, stay the same for the life of the boat.
What the 12 characters mean
Boats certified after 1 August 1984 use one standard layout. Reading it left to right:
- Characters 1–3 — the Manufacturer Identifier Code (MIC). A three-letter code assigned to the builder.
BEY, SER, GDY and so on. - Characters 4–8 — the hull serial number. The builder's own five-character serial for that hull. The letters I, O and Q are not used, because they are too easily confused with 1 and 0.
- Character 9 — the month of certification. A letter from
A (January) through L (December). - Character 10 — the last digit of the year of certification.
- Characters 11–12 — the model year.
Worked example: in BEYN6044G506, BEY is the builder, N6044 is that builder's serial for the hull, G is July, 5 is 2005, and 06 is the 2006 model year. So the hull was certified in July 2005 and sold as a 2006 model — which is why a boat's "year" often depends on which year you mean.
Why the HIN matters more than the boat's name
Ask two people about a boat and you get two different answers about which boat they mean. A name gets repainted. A state registration number changes when the boat moves. A dinghy, a keel and a suit of sails can all be swapped.
The HIN is what lets anyone — an owner, a surveyor, a yard, an insurer, a buyer — be certain they are all discussing the same hull. That is why records worth keeping should be attached to the HIN rather than to a name or a registration: they then survive a sale, a re-name and a move to another state.
Where the HIN appears
There are usually two on a boat. The primary HIN is on the outside of the hull, at the upper starboard corner of the transom, where it can be read without dismantling anything. A duplicate HIN is placed somewhere unexposed — inside a locker, under a fitting, beneath the deck — so a hull can still be identified if the transom is damaged or the primary number is removed.
The same number should also appear on the boat's registration or title, its insurance documents, and its bill of sale. If those disagree with the hull, stop and resolve the difference before money changes hands.
For the practical hunt — including boats with no usable transom, personal watercraft and inflatables — see How to Find the HIN on a Boat.
Older boats and boats from outside the US
Two cases regularly confuse people:
- Boats certified between November 1972 and August 1984. Two earlier 12-character layouts were in use, and the date characters do not sit where they do today. Do not assume the modern month-and-year positions apply to a 1970s hull; confirm the build date with the builder or the paperwork instead of decoding it.
- Boats built for the European market. These carry a 14-character Craft Identification Number (CIN) that begins with a two-letter country code before the manufacturer code. An imported boat may carry a CIN, a HIN, or both. Record exactly what is on the hull, character for character, rather than tidying it into the format you expected.
Where a boat has been re-hulled, rebuilt, or assigned a state-issued replacement number, the number on the hull is still the authority. Write down what is physically there.
What a HIN does not tell you
This is where a lot of online advice overreaches. The number itself encodes the builder, a serial and a date. It does not encode:
- who owns the boat, or who owned it before,
- whether money is owed against it,
- whether it has been in an accident, sunk, or repaired,
- how it has been maintained.
None of that is in the characters. It exists — if it exists at all — in separate records: state title files, US Coast Guard documentation for documented vessels, survey reports, yard invoices, insurance files. A HIN is the key those records are filed under, not the records themselves. Anyone promising a complete history from a number alone is selling you something.
Check a hull now
VesselBook keeps a boat's records against its HIN, so they stay with the hull rather than with an owner. The free HIN Lookup shows what is publicly on file for a hull: its identity, whether ownership has been verified, the records an owner has chosen to make public, and whether the hull appears in federal vessel data. No account is needed, and an empty result simply means nothing public is on file yet — it is not a verdict on the boat.
If you own the boat, the more useful direction is the other one: records you file now become the history the next owner, surveyor or insurer can actually see. That is what the Trust Score reflects — how well documented a hull is, not how good a boat it is.