While the hull number sequence has changed over the years, the following will help to "De-Mystify" what all those numbers mean on the upper right hand side of the transom.
The hull number is part of the Hull Identification Number (HIN) which is molded into the transom. The HIN is located on the outside of the stern in the upper starboard corner. In many states the HIN is on your title.
Note: The following applies to HINs after August 1, 1984. For more info about numbers prior to this date, see: http://www.boatsafe.com/nauticalknowhow/hin.html
PCW=The U.S. Coast Guard identity for Precision Boat Works.
21=Model or Size of Precision boat
302=Actual number for the boat, or number of hulls produced to that date (HULL NUMBER)
B=Month of hull lamination where A=January, B=February, C=March, etc.
3=Year of lamination.
Items may change on each model of boat due to improvements, new suppliers, or unavailability of older parts. These changes might happen in the middle of the model year. The hull number is a unique, sequential serial number. When you call the factory to order parts or ask a question, they may ask for your hull number. This is the only way they can identify what is exactly on your particular boat.
Sails shipped with new boats from the factory come with hull number digits in the sail bag which can be placed on the sail. You may be able to just look at the sail to see your hull number, although not all owners have applied the numbers to the sail. Also, used sails may have different numbers. It is always best to check the HIN on the transom.