The relevant section of the class rules:-
2.4 Registration and Measurement Certificate
2.4.1 No boat is permitted to race in the class unless it has a valid measurement certificate. This rule may be suspended in the case of charter boats at any event with the permission of the IODA Executive Committee.
2.4.2 Each National Authority shall issue sail numbers which shall be consecutive and the number shall be preceded by the national letters. Numbering may restart at 1 on reaching number 9999. A National Authority shall issue a sail number only on receipt of evidence that the building fee has been paid.
2.4.3 The certificate is obtained as follows:
(a) The builder shall have the hull measured by a measurer officially recognised by his National Authority. The Registration Book with the ISAF International class fee receipt, builder's declaration and hull measurement form section completed shall be supplied to the owner of the boat.
(b) The owner shall apply to the appropriate National Authority for a sail number enclosing their Registration Book with builder's declaration and building fee receipt. The National Authority shall enter the sail number in the Registration Book.
(c) The owner is responsible for sending the Registration Book with the builder's declaration and all measurement form sections completed to his National Authority, together with any registration fee that may be required. On receipt of this the National Authority shall complete the measurement certificate section of the Registration Book and return it to the owner. Note that where a National Authority prefers to issue its own certificate this shall be firmly fixed to, and mentioned in the Registration Book.
2.4.4 Change of ownership invalidates the measurement certificate but shall not necessitate remeasurement. The new owner shall apply to his National Authority for endorsement of the certificate/Registration Book returning it with any re-registration fee required and stating the necessary particulars. The measurement certificate/Registration Book shall then be returned to the owner