Another try...
Okay, with thanks to the intrepid data miners out there, here goes another try. The reason that the serial number looked defaced and the reason it's so hard to read is that there appear to be TWO serial numbers, one stamped on top of the other!
Perhaps it would be wise to check both OT and Carleton records. Could it have been started as OT and then renumbered and sold as Carelton, or vice-versa?
The number I've been trying to post now looks more clearly like 1666x5 17. The 4th position seems to have a curve at the top pf the digit, so maybe 0, 2, 3, 6, 8 or 9. And I'm not at all positive about the 5th digit.
The OTHER serial number looks like 694x4. There's a hint of a long-ish straight line a the top of the 4th position, which may mean 5 or 7.
See attached photos. The "166x5" (if that's what it is) seems to be a sharp, deep stamp right in the middle of the stem. The other number is lower on the stem (more toward the edge), and seems to be made with a wider-font stamp. Note that the length ("17") is put on with the wider-font stamp, so I think the "694x4" was original and was over-stamped with "166x5". According to the OT chart, "69xxx" would be around 1922 and "16xxx" would be around 1912. When would a "16xxx" Carleton have been produced? Maybe in the early 20s?
More info- mahogany inwales, outwales, thwarts, seats. Set up for sailing. OT-style gudgeons installed the way OT did. No half ribs, but there was a floor rack. Outside stems. Open gunwales. Bolts of steel, countersunk and bunged. Looks like white cedar ribs and red cedar planking. Outside stems oval in cross section. Decks and kingplanks put on with tiny nails- not screws. Coamings put on with oval-head screws, as typical for OT.