Every optimist in the world is issued a measurement book before it is sold.  By registering your optimist with USODA, you keep that measurment book valid.  If you ever take your boat to an event where they require a measurement book/certificate, you will need to show that it has been properly registered in your name with USODA

Every hull has a unique ISAF / World Sailing number associated with it.  That number can be found on a plaque that is affixed to the aft-facing side of the mast partner.   It's comparable to a VIN number on an automobile or boat.  DO NOT REMOVE OR ALTER THIS PLAQUE!!!

It may look like one of these:

When a boat is measured by a builder, they complete the measurement book, which includes the ISAF / World Sailing Plaque number.  That number is provided to USODA, and we assign a sail number to go with it.  That sail number and plaque number are 'married' to one another.  If you are unsure of the sail number that goes with your boat, email usoda@usoda.org and provide the ISAF / World Sailing Plaque number.  We will then be able to provide you with the sail number that goes with your hull.

At USODA events, the sail number you register with must be associated with a boat registered to you (exceptions are made when sailors are using club-owned boats, and also for Green Fleet sailors).  This process eliminates duplicate sail numbers at an event, which would be a nightmare for race officials and scorers!!