It will carry 20A easily don't have the IET regs handy it should be able to carry at least 40-50A.
But it would be no good as a shore supply cable as it is not flexible
Even if you get a single phase to three phase convertor the output of the convertor would depend upon what the supply amperage, which I would suspect not be large enough over the three phases to supply your equipment onboard.
Plugging into different sockets on the berth may cause other problem...