French continued to be taught among the gentry after English became the common language in England by act of Parliament in 1362. A lot of legal documents and treatises were written in French (even in England) well into the 18th century. French remained a strong language in day to day diplomacy and commerce so that even final treatises of the Spanish War of Succession were written in French.
During the 18th century the middle class (in a desire to be perceived as 'refined') continued to teach French at home along with Italian due to the influences of art, music and literature in society. However, it was common for boys to be taught 'ancient' Latin and Greek, while the 'modern' languages of French and Italian were taught to girls.
I'm not certain how this effects bilingual numbers among sailors and officers of the navy or further out to buccaneers, but if you study any etymology, you constantly see that word origins begin in French all the time. English as a developing language owes a lot to French.