inside boat
The 12-digit HIN, or Hull I. D. Number was not required until the 1973 model year, the requirement went into effect on November 01, 1972. O'Days built prior to that time have a mettal plate affixed to a bulkhead or flotation tank with 2 numbers on it. There is a Hull # and a Class #. Hull # refers to the total number of O'Days built and Class # refers to the number of that model built. Using my (1969?) Widgeon for an example, Hull# 22698 Class # 1791, means that she was the 22698th O'Day built, and the 1791st Widgeon. The plate may have fallen off before you bought your boat, or been removed by a previous owner to paint where it was mounted.