Bond requirement for export in small vessels: duty-free release allowed subject to bond, proof of landing, or forfeiture. Export of warehoused goods in vessels below the prescribed size is allowed without payment of import duty provided the exporter or vessel agent executes a bond equal to the import duty, in the form and with such surety or security as the proper officer requires; the bond is discharged on production, within three months or any extended period allowed, of a customs certificate from the port of destination showing the goods were landed, otherwise the amount equal to the import duty for which no certificate is produced shall be forfeited.