If you are certified to sail in another country then send your certification to the national governing body in your country and ask them to issue a HOCC (Helmsmans Overseas Certificate of Competency). You may get away with your certification as it stands but officially you should have the HOCC as far as I am aware. It also depends on what you qualified in, if you qualified in a dinghy then they may not cover you to sail a 30 foot keel boat.