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I read the FAQ about identifying model year but on my 17 Montauk but [the stencil number and the federal HIN] do not match.
The stenciled transom says 3C3597 and the metal plate in the bow stowage says BWCJ7084F586, which I interpret to mean it was built June 1986.

Q1: [do you have] any ideas on [why the number in] the stenciling [does not match number the federal hull identification number]?

o8er wrote:Q1: [do you have] any ideas on [why the number in] the stenciling [does not match the federal hull identification number]?

Yes. I have an idea: the stencil number and the federal hull identification number are never the same number.

The FAQ explains both numbers is detail. You probably should read it again.

The stencil number conforms to Boston Whaler’s in-house system for identifying and tracking hulls as they are being molded. There is no encoding of a model year into the stencil number, as they are generally used sequentially.

The federal hull identification number conforms to the federal regulations imposed on all boat builders in order to sell the boat in the USA.

That you have made an inference the two numbers should “match” is an error.

Read at

https://continuouswave.com/whaler/reference/FAQ/#Q2

You have also made an error in interpreting the HIN. The HIN (using the “new” format) shows the boat was built in June 1985 as a 1986 model year boat.

Also, the HIN being on a metal tag is a bit unusual for a boat made in 1985, as the requirements specified a molded-in or permanently attached method. This topic is discussed at great length at

Method of Indicating Federal Hull Identification number
https://continuouswave.com/forum/viewto ... 442#p46442

Thank you for clarifying the [the nature of the stencil and the federal hull identification] numbers. What I was looking for was my model year. I'm a new owner of a--now I know--a 1986 Montauk.

There's a metal plate on the starboard transom that has the same number as the [metal tag in the anchor locker] except it seems to be missing the "J".

o8er wrote:There's a metal plate on the starboard transom that has the same number as the [metal tag in the anchor locker, except it seems to be missing the "J".

As explained in the FAQ answers to which I pointed and gave a hyperlink in my earlier reply, Boston Whaler often pre-printed the metal tags with certain elements of the HIN which would be repeated on many HIN tags to be used in a run of production, including, for example, a prefix character in the PRODUCTION SEQUENCE NUMBER, such as, in this case, the leading character "J." The absence of the "J" prefix on the tag affixed to the transom is likely due to exposure to the weather over the years or from some abrasion used in an attempt to clean off the HIN tag which accidentally removed the ink of the "J" from the tag. Again, this is explicitly mentioned in the FAQ in the answer to Q2 and in the paragraphs under the sub-heading "Missing Letters or Numbers on Metal Tag."

o8er wrote: I'll likely re-visit the write-up one day,

You might try reading the FAQ again before asking more questions, as the FAQ is actually intended to provide comprehensive answers to the most frequently asked questions.

Here is all the information that can be extracted from the federal HIN number on your particular boat:

First, FROM THE FAQ we see this HIN is in the "new" format (used after August 1984) which encodes the HIN according to this schema:

MIC-NNNNN-P-Y-ZZ

  MIC = Manufacturer's ID Code  BWC=Boston Whaler
NNNNN = 5-character production or serial no. 
    Y = Year of production
   ZZ = Model Year

HIN = BWC J7084 F5 86

BWC = the manufacturer identity code or MIC for Boston Whaler

J7085 = the five-character production sequence number of this hull

F = the month of production, according to the scheme F indicates June

5 = the year of production, deduced to be 1985 based on the model year two-digit year

86 = the model year, deduced to be 1986, as only two digits are provided

ASIDE: that the stencil number on your particular ended with two digits ("97") that could have been the last two digits of a year in the possible years of production for this boat is just a complete coincidence, and to have inferred that the last two digits of a stencil number must be an encoding of the year was incorrect on your part.

The stencil number has only six characters, and to use two of the six to indicate a year of production would have left only four characters available for Boston Whaler to encode the production sequence of the every hull ever made for all time.

ASIDE

o8er wrote:What I was looking for was my model year.

Your initial post never mentioned anything about confusion of model year, but I was able to INFER that must be what you were asking about when I noticed that the last two digits of the stencil number could have been mis-interpreted as being a year. When creating a post, a good approach is to be very specific in your statements, as readers are not mind readers.