It means that an American vessel trading across the Pacific Ocean is going to have to have every "man jack" of her crew a Caucasian or a negro or else she can not enter an American port. It means the same thing for every British vessel. It will have to be manned by Americans. or Britons. or Europeans. or Africans. it can not have a single Malay or a Chinaman or a Japanese in its crew. On the other hand. there is an exception in this section that allows a ship under the Chinese flag to come in with her crew of 100 per cent Chinese. So also every Japanese ship may come in with every individual in her crew a Japanese coolie. if you please.
Identified stereotypes
Generalization about Chinese and Japanese laborers ('coolies') as being universally employable on ships.