区别就是两者意思是不一样具体的不同如下

captain中文意思是n.

船长;机长;(海军)上校;(陆军或美国空军的)上尉;首领;领导者;(尤指运动队的)队长;（美国警察局的）副巡长;

vt.

担任…的队长(或船长);

例句

The captain gave the order to abandon ship.

船长下令弃船。

shipmaster中文意思是船主And every shipmaster, and all the company in ships, and sailors, and a many as trade by sea, stood afar off.