During the late 1600's and early 1700's, women in Europe had few, if any rights to speak of. The most status a woman ever got in her life was if she was married to someone else of high status, and even then, she was considered the property of her husband. While unmarried, women had a bit more freedom, but were still considered the property of their father.
There were still a handful of women who wished to have more than they were endowed with, and many times, the way to be treated as an equal to man was to dress like one. At the time, it was not considered appropriate for women to wear trousers or men's clothing, so many women were able to easily pass as men without recognition. However, if women were caught posing as men, the penalty could be steep. Out at sea, it was not unheard of for women to be killed if they were caught aboard a pirate ship.
As romantically as pirates are portrayed in modern movies such as Pirates of the Caribbean, often times, this is not an entirely accurate portrayal. Life aboard a pirate ship was often miserable, coming as a result of a lack of fresh food and clean water. Pirates were often malnourished and lived unhealthy lifestyles, which encouraged the spread of disease. Men aboard ships suffered and died from a multitude of diseases, many of them preventable and treatable, simply because they did not have access to proper medical care while at sea.
And, as brotherly as pirates might seem on the big screen, often this was not the case either. Men usually did not get along on pirate ships, and spending time in close quarters didn't always bring them closer together. The hierarchy of power aboard pirate vessels was not always a reality either, and often times, men worked as laborers on a ship, rather than having specific ranks. Brotherhoods were not commonplace; murders and mutinies were not unheard of, and even captains were targeted.
Still thinking the pirate life's for you? Yeah, me neither.