The US does not recognize any foreign license as being of equivalent competence, although of course the UK and others recognize the US license as of equivalent competence. go figure.
Why would you need to change jobs if you wanted to emigrate can't you just stay working where you are now? - that has to be one of the main advantages of a life at sea.
moving to the US is not easy. It's not anything like moving to other EU countries. Often your best bet would be to be sponsored there by a company.