Tortuga:
Not what books, what tropes. What elements.
As i said for me it would be plausibility of the setting in terms of whether piracy can reasonably exist under the given scenario.
I mean once you strip it of all its trappings pirate is really just another word for mugger. They are criminals with a profit motive who assault and murder people, en mass, for their possessions. As a viable business model that requires a few basic preconditions.
1) Enough economic activity. Unless the society they prey upon produces
sufficient wealth to make stealing it worth risking your life there is
really no point in being a pirate.
2) A market. Popular fiction notwithstanding most of what a pirate can
expect to seize in terms of loot will not be cash or other forms of
liquid, anonymous wealth. That means there has to be a way to fence
their victims former posessions for legal tender. That in turn implies a
legitimate country willing to act as a laundromat for stolen bulk
cargoes, be it as a weapon of economic warfare against its rivals, for
a share of the take, or both.
3) A safe haven. Pirate vessels, be they spaceships, zeppelins, or
drakkar need maintenance, and provisions, and their crews a place to
actually be able to spend any of their illgotten gains. That means a
port or rather ports able and willing to provide both in defiance of
whatever authorities the pirates have offended with their activities.
Usually that takes the form of (as above) a state actor extending the
cover of its souvereignity because its a cheap or even profitable way to
damage their rivals without officially going to war, or augmenting your
forces if you already are at war.
Alternatively you'd need an extended period of anarchy or military
overextension where none of the legitimate countries has the forces to
spare to suppress local warlords and prevent them from renting out their
infrastructure to the raiders for a cut.
4) Being a livable evil. Pirates are parasites. If their predations
destroy the economic base of the country whose ships and towns they
attack they kill off the very host their own livelihood depends upon. No
profit, no trade; no trade, no loot; no loot, no pirates.
If pirates are an existential threat rather than a calculated, and
calculable, risk to the movement of wares and people it also tends to
make eradicating piracy a political priority, which historically spells
the end for the pirates in fairly short order as the bases they depend
upon get captured or razed (Shing Shi is the only example i can recall
where the pirates arguably won that sort of full on confrontation, and
even she ultimately decided to cash in her chips and make a deal while
she was ahead).
