Just a hunch Gunna, but try writing to your local/national Merchant Navy/Marine org and asking them for a heads-up on requirements for entry (whether you need to join a union or the 'service' itself - I'd give the RNZAF a skip though, as your f*cked-up Prime Minister has effectively killed that off.
Or, get in touch with outfits like P&O or Fred Olsen Lines. Are White Star Line still going??
Not sure of the pre-requisites for an ocean-going engineer, i.e. what type of ticket you'd need to hold or get before being allowed to get underway. Have you done any work on either gas or diesel turbines??