With a HIN ending in F505, I think "legally" there isn't really any way your boat can be anything but a 2005. A dealer may have called it a 2006, or an owner may have thought or "decided" it was a 2006 and registered it as such. I don't say this because it really makes any difference. Sort of like how you don't suddenly become anything more than one day older on your birthday. And it's not like the boat changed shape or design from 2005 to 2006.
But officially, here is how the last four digits work (which was explained above, I'm just saying it again, really).
The first pair of the last four digits signify when the hull was laid (in other words, when they started building the boat). The letter is the month (January is A, February is B, etc.), and the number is the year. So the hull was laid for your boat in June of 2005. The last pair of digits are the official model year. So the 05 says your boat is a 2005.
Not all boats have the same years in the two pairs of digits. For example, my boat's hull was laid at the end of 2001, but it is a 2002 model boat. So my HIN ends in something like L102 (i.e. December of 01 hull laid; 2002 model boat). Yours was begun in 2005 and is also a 2005 model year (which makes sense for a mid-year start).
Although there are usually a few "mysteries" such as Thataway points out, because boatbuilding is not always totally predictable (like, say, cars would be). Maybe they start a 22, but then five 25's get ordered, so the 22 is set aside and they build the 25's, then later get back to the 22. Or maybe they laid a green 22, but then orders come in for seven blue ones so it gets set aside. With the last four digits, you know (or at least there is some accountability presuming no hijinks) that you don't have a boat that was begun five years ago and just sat around (no idea how they keep those records though).
Maybe more than you wanted to know, but hey, always fun to talk about your new boat, right?
