How old is my boat?

This is the best-answered question on the whole site, and the reason is that nobody had to be asked. Every boat sold in the United States carries a twelve-character Hull Identification Number, and the US Coast Guard set out in law exactly what each character means. No manufacturer chart, no permission letter, no page that might be withdrawn.

It also does something none of the other schemes here manage: it tells you the year twice, to two different precisions, three characters apart. One of those is ambiguous on its own. The other fixes it.

What the twelve characters are, in the Coast Guard's words

33 CFR 181.25 — readable at the eCFR — requires that a HIN “consist of twelve characters, uninterrupted by slashes, hyphens, or spaces”, and then says what they are:

The year that is ambiguous, and the year three characters later that is not

Character ten is “the last digit of the year of manufacture or certification”. One digit. A 4 there means 1984, 1994, 2004, 2014 or 2024 — the same ten-way ambiguity that sits under half the pages on this site.

Characters eleven and twelve are the model year in full: “such as ‘82’ for 1982”, which is the Coast Guard's own example. Two digits, so no ambiguity worth the name.

So the rule puts the problem and its answer three characters apart. A boat whose model year reads 04 and whose build digit is 4 was built in 2004, and nothing else fits. This page uses the model year to resolve the build digit and says so on screen, because that is a deduction rather than something the regulation spells out.

They are not the same thing, and the page keeps them apart. The build date is when the hull was certified or assembled; the model year is what the builder chose to call it. A boat built in October is very often next year's model, which is why a HIN can read October 2003, model year 2004 without anything being wrong.

The month letters, and what we are continuing rather than quoting

The regulation names three of the twelve: “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.”

A–L for January to December is our continuation of their sequence, not a table they printed. It is not in doubt — twelve months, a stated start and a stated end — but it is a different kind of statement from a quoted chart, and this site marks the difference. The HVAC page does the same with Trane's days of the week, where only three of six are actually printed.

Three bodies, three answers, one agreement

The HIN serial may not use I, O or Q. Two other schemes on this site solve the same problem — characters too easily misread — and reach different answers:

Two federal agencies and an engine builder in Wisconsin, working separately, all agree that I, O and Q are the dangerous ones — and disagree about everything after that. There is no standard for what counts as confusable, only conventions. The three-way comparison above is computed from the three sources rather than typed out, so it cannot quietly go stale.

What this does not cover, said plainly

Boats built before about 1984. HINs have been required since 1972, but the twelve-character arrangement above comes from a later amendment. The regulation as it stands today does not describe what came before it, so neither does this page, and the decoder says so rather than guessing when a number does not fit.

Boats from outside the United States. The rule covers boats made for or imported into the US. Coast Guard rules allow an importer to use another nation's system where one has been accepted, so a foreign-built hull may carry something else entirely.

The engine is a separate question with a worse answer. See below.

The outboard on the back is a different story

The hull is covered by law. The engine is covered by whatever its maker chooses to publish, and mostly that is where to find the number rather than how to read it.

Honda Marine are typical and are at least precise about it: their serial number locator says the number “is found on or near the stern bracket, stamped into a metal plate” and takes the form BXXX-XXXXXXX — and says nothing about a date being in it. Knowing where to look is genuinely useful and is not the same as knowing what it says.

Two makers appear to publish more, and we could not read either. Tohatsu have a page titled Find out model year, and Mercury Marine have an article on locating the engine serial number. Both render entirely in JavaScript, so a fetch returns navigation and nothing else. Both are linked above so you can open them yourself, which is the point. We are not going to tell you what is on them. There are write-ups elsewhere claiming to summarise both, and none of it comes from a page this site has read.

What was checked

The pool is 326 marine engine and boat makers, listed in marine-makers.txt, built from Wikipedia's marine engine manufacturer and boat builder categories, with websites from Wikidata's official-website property rather than guessed at. Two further categories were tried — outboard motor manufacturers and motorboat manufacturers — and neither exists, so neither contributed anything. This page used to name all four as sources, which claimed more than the sweep covered.

And read the swept figure knowing how much was there to read. Of the 123 counted as swept, 46 offered this method fewer than 25 pages to look at, and 41 of those offered nothing from a sitemap at all. A host that answers, allows us, and then has almost nothing to search still counts as swept. It is the number of doors opened, not the number of rooms searched.

Of the 44 not probed: 34 did not answer at all, 5 returned 403 on robots.txt itself, 3 block us by name, and 2 read fine and then refused the page.

Read the swept figure as swept, not as cleared. This method has demonstrably missed makers who do publish, on Zippo, Ludwig and Rheem. It is also blind to anything behind JavaScript, which on this family is where two of the most promising pages turned out to be.

Eight candidates, and three different meanings of the word

The sweep looks for serial and its equivalents in seven languages, and this family is the first where the word's other English senses outnumbered the one we wanted. Of eight candidates:

That is the ninth, tenth and eleventh time a word has matched something it should not on this project — after “stamp”, updating, package of, thin-film and the rest. The pattern is always the same: a word that is a whole word in the target sense is also a whole word in three other senses, and no amount of care with boundaries fixes that. It is why every candidate is opened by a person before anything is written down.

Building the list

Makers go in by a positive test: a company is filed on Wikipedia under a category containing “companies”, “manufacturers”, “corporations”, “businesses” or “brands”, and anything with none of those is dropped and reported. 127 entries went that way.

Seven well-known boat builders were checked by name and are not in the pool, because Wikipedia has no article for them: Torqeedo, Selva Marine, Nanni Diesel, Grady-White, Lund Boats, Bertram Yacht and Hatteras Yachts. Each was searched for rather than assumed missing. That is a gap in the source, not in the trade, and it is the same gap the pedal page found — a maker list built from an encyclopaedia inherits the encyclopaedia's blind spots.

One category that does exist was deliberately not used: Shipbuilding companies. A shipyard building tankers is a different question from a boat with a HIN on its transom, and the Coast Guard rule this page is built on applies to recreational boats. That is a decision rather than a gap.