Is it necessary to be trained as a sailor? You just need to be trained to verify it, right? What mechanic sailor? I'm talking about the crew of the cargo ship. Of course.
Crew members must have received professional training. Non-nautical majors must attend at least one year's training after training in colleges or specialized training institutions before they can take the seaman's certificate examination. The A&B mechanic sailor you mentioned is a class A or B navigation area position, and of course there is a class C. Both classes A and B can run the ocean, and the class C is generally the domestic north-south line or Southeast Asia. If you want to go aboard, you must have a certificate. It's all a radish and a pit. I dare not send specific training institutions here. It seems that I am advertising, and I can't answer it or submit it. You can search for crew training institutions in Baidu.