A boat HIN is exactly 12 characters, and it splits into three blocks: a 3-character manufacturer code, a 5-character serial number, and a 4-character date. Once you know where the boundaries fall you can read a build date off any hull in about ten seconds.
| Position | What it means |
|---|---|
| 1–3 | MIC — Manufacturer Identification Code, assigned by the US Coast Guard |
| 4–8 | Hull serial number — the builder's own sequence, no fixed meaning |
| 9 | Month of manufacture as a letter, A = January to L = December |
| 10 | Year of manufacture — last digit of the year the hull was built |
| 11–12 | Model year — two digits |
Twelve letters, in order, skipping nothing: A January, B February, C March, D April, E May, F June, G July, H August, I September, J October, K November, L December. If character 9 is a number rather than a letter A–L, you are almost certainly looking at a pre-1984 hull — see below.
Take a real hull number from a published Coast Guard recall record: BWCE1053K819.
| Block | Reads as |
|---|---|
| BWC | Boston Whaler Inc, Edgewater, Florida |
| E1053 | Hull serial number |
| K | November |
| 8 | Built in 2018 |
| 19 | Sold as a 2019 model |
So: a Boston Whaler hull laid up in November 2018 and sold as a 2019 model.
This is the single most common source of confusion, and it is not an error. Boat builders run model years like car makers — production for next season starts in the autumn. A hull built in September, October or November is routinely sold as the following year's model. A HIN reading “K819” is not contradicting itself; it is telling you both facts at once. See finding your boat's model year for why this matters when you insure or resell.
The current format was standardised in August 1984. Before that, the last four characters ran in the opposite order: two digits of year, then two digits of month. So a 1979 hull built in June ends “7906”. Any date block that is four straight digits is being read under the old rules, and only years 1972–1984 are valid there.
HINs are stamped, and stamped characters get misread. The usual culprits are 0 and O, 1 and I, 5 and S, 2 and Z, and 8 and B. If a decode fails, retype it substituting each of those before concluding the number is bad. A HIN also never contains spaces, dashes or punctuation, so strip anything like that before entering it.
Type the 12 characters from your transom and get the model year, build date, manufacturer on record and open recall status — free, no account needed.
Run a free HIN checkNew to hull numbers entirely? Start with what a HIN is. Not sure where to find yours? See where the HIN is located.