Piracy -- all attempts to Google 19th century piracy turn up early stuff. Like the Barbary pirates and the US Navy being sent against them by Jefferson. I know it was heavily suppressed throughout the century, but were there any hot spots in the later times?
The British army had rankers -- the non-gentleman variety, enlisted soldiers who got a commission. Were there equivalent figures in the navy? Was it more likely, or less? Was it as social difficult as it was in the army? Googling victorian navy with commissions and the like seems to turn up army stuff, and details about the officers and the sailors.
And while we're at it, are there any books that cover the social and day-to-day aspects of life in the navy at that time? Any navy, because I think there will be encounters between different navies, and I may want to steal from more than one.