Navigate to https://www.sunfishclass.org/membership/join-the-class. Fill out the form and pay the dues. You will receive an email from the association showing the sail number assigned to you.
If you already have sails with numbers, and you would like to use that number, you may petition the association to keep that number. Whether you get to use the number depends on if the person to which the number is assigned is still an active member/using the number. Email sunfishoff@gmail.com to petition for a number change. You may also get additional numbers (for additional boats) assigned to you using the same email address.
New or replacement numbers shall be a minimum of 300mm or 11 13/16”, easy to read, and either rounded in shape or digital "8" style. These styles of numbers may be purchased through marine suppliers.