Werbil,
As Lasiorhinus says an MSIC is the maritime equivalent iof an ASIC, required if you need to be inside the fence at Australian commercial ports, on Australian registered ships (don't know what the cutoff size is) or on offshore installations in Australian waters (read oil rigs and platforms, etc.). They are cracking down on rotary wing aircrew in offshore and MPT operations.
Cheers,
SFB