How to read a HIN
Every HIN is 12 characters with no spaces or dashes. The first eight identify the builder and hull; the last four encode the date — in one of three formats depending on when the boat was built. The decoder figures out which format applies automatically.
Current format
August 1, 1984 → todayCharacter 9 is a letter A–L for the month of certification (A=January … L=December); character 10 is the last digit of the certification year; characters 11–12 are the model year.
Straight-year format
November 1, 1972 → July 31, 1984The oldest post-standardization format: characters 9–10 are the two-digit month of production and 11–12 are the two-digit year.
Model-year format
Legacy (a common 1970s–1980s variant)A literal M in position 9 marks this format. Positions 10–11 are the model year and position 12 is a month letter with a DIFFERENT mapping — A=August … L=July.
Where to find your HIN
The primary HIN is permanently stamped on the starboard (right) outboard side of the transom, within two inches of the top of the transom, hull side, or rail (33 CFR 181.29). Boats without a transom carry it on the starboard side aft. A duplicate HIN is affixed in an unexposed spot elsewhere on the hull, so a builder can still identify a stolen or re-fiberglassed boat. It also appears on your title, registration, and — for larger boats — insurance paperwork. If the HIN on the hull doesn't match the paperwork, or looks altered, stop and verify before buying.
Frequently asked
What is a HIN (Hull Identification Number)?
A HIN is a 12-character code that a boat's manufacturer permanently affixes to the hull, required on every boat built or imported since November 1, 1972 under 33 CFR Part 181. It's the boat equivalent of a car's VIN: it identifies the builder and the specific hull and never changes for the life of the boat.
Where do I find the HIN on my boat?
The primary HIN is permanently stamped on the starboard (right-hand) outboard side of the transom, in the upper corner, within two inches of the top of the transom, hull side, or rail (33 CFR 181.29). A duplicate is affixed in an unexposed location elsewhere on the hull. On boats without a transom it's on the starboard side aft.
What do the 12 characters of a HIN mean?
Characters 1–3 are the Manufacturer Identification Code (MIC) assigned by the Coast Guard to the builder. Characters 4–8 are the builder's serial number for that hull. Characters 9–12 encode the date: on current-format HINs that's a month letter, a certification-year digit, and the two-digit model year.
How do older, pre-1984 HINs work?
Two legacy formats exist. The straight-year format (1972–1984) uses a two-digit month then a two-digit year in positions 9–12. The model-year format uses a literal 'M' in position 9, the model year in positions 10–11, and a month letter in position 12 — but with A=August … L=July, a different mapping than the current format. This decoder detects and handles all three.
Why can't a HIN contain the letters I, O, or Q?
The letters I, O, and Q are excluded from the serial portion of a HIN because they're too easily confused with the digits 1 and 0. If you read an 'O' or 'I' in the middle of a HIN, it's almost certainly a zero or a one.
How is a HIN different from an official number or a state registration number?
The HIN is the permanent hull code the builder affixes at manufacture. A state registration number (the bow number, e.g. 'FL 1234 AB') is assigned by your state and changes if the boat is registered elsewhere. A USCG official number is assigned by the National Vessel Documentation Center to a federally documented vessel and marked inside the hull. A boat can have a HIN plus either a bow number or an official number.
Can a HIN tell me who owns the boat?
No. A HIN identifies the builder, hull, and build date only. Owner names are not part of the public record — the Coast Guard has redacted individual owners' names from public vessel data since 2017 — so no free or paid HIN lookup can return a current owner's name from public sources.
Is this HIN decoder free?
Yes. Decoding is done entirely in your browser against the 33 CFR 181 format and is completely free, with no sign-up. When your HIN matches our database we also show the manufacturer and any USCG-documented vessels built under that MIC.
Last verified:
Primary sources
- 33 CFR Part 181 Subpart C — Hull Identification Numbers (§ 181.23–181.31: format, display, and required positions) (retrieved 2026-07-15)
- 33 CFR 181.29 — Hull identification number display (permanent HIN on the starboard outboard side of the transom) (retrieved 2026-07-15)
- USCG Boat Builder's Handbook — Hull Identification Numbers (format, month/year coding, pre-1984 formats) (retrieved 2026-07-15)
- USCG Manufacturers Identification Code (MIC) database — look up the builder behind a MIC (retrieved 2026-07-15)
Keep reading
Independent reference tool — not affiliated with, endorsed by, or sponsored by the U.S. Coast Guard or the National Maritime Center. Vessel data is derived from public USCG sources and may lag official records; always verify with the issuing authority.