It should not matter whether one uses “female” or “woman” as an adjective for a ship captain or some other person. Both are grammatically correct. But in this age of political correctness and fragile sensitivities, some rabid feminists may object to the use of “female” as exemplified in this headline of a CBS News story:
The objectors would argue that the adjective “female” draws too much attention to the reproductive system (read this article from The New Yorker: ‘Female Trouble: The Debate Over “Woman” as an Adjective’). It is somehow debasing. They would insist on using “woman” as in this Forbes story headline:
As defined in any English dictionary, a woman is an adult female human being. The adjective “female” means having the attributes of a woman, which typically includes the capacity to bear young. Today, however, biological sex is no longer synonymous with gender identity. An individual can choose to be identified as a male or a female.
But why even emphasise the sex or gender of a ship captain? The answer is simple. Although more and more women can be seen behind a ship’s helm, they remain a relatively small tribe in a male-dominated industry. Their sex or gender is worth mentioning. To call them “female ship captains” or “women ship captains” really makes no difference. Both descriptions are a testament to their struggles and achievements as professional women.