There are already RPG games that focus on swashbuckling campaigns. They're lighter in tone, and feature the cinematic action, or perhaps a bit of politics and intrigue. I'm coming at the pirate genre from the perspective of horror fantasy; ghost-haunted ruined Spanish castles on lonely promontories; dank swamps with zombie masters, jade idols, and mindless undead hulks; fallen jungle ruins with blasphemous temples and a fortune in gems. The idea is to make a large wilderness hex crawl, a "saltbox" instead of a sandbox, with the sailing vessel as the primary conveyance. The mode is D&D style play, exploration seeking after treasure, but with the chance for a bit of opportunistic piracy on the high seas (both for and against the players), and some rowdy carousing back in Port Royal or Tortuga.
The challenge is to build simple, abstract, flavorful nautical rules that capture situations during the Age of Sail without requiring a lot of nautical interest to enjoy the style. So far, the ship combat rules in Flashing Blades: High Seas (FBHS) strike a good tone of abstraction and flavor when compared to the fiddly bits in competing rules sets, but there are a few things to change and/or add, to adapt them to D&D style play.
First thing to add is some basic skill resolution for professional skills - unskilled, skilled, expert, master - for specialized (non-adventuring) skills like sailing, navigation, and gunnery where resolution is going to matter. Plenty of OSR types have adopted 2d6 skill systems modeled after the reaction roll chart. Player characters can gain knowledge of professions over time, but the system is mainly for determining how hired experts contribute during a conflict.
An important segment of a nautical encounter is when sails are spotted on the horizon, quickly followed by a decision to evade or give chase; the zoom level of FBHS is a little too tactical (yards instead of miles), skipping the whole dynamic of evading until night fall to escape the pursuer after dark, or using fog and foul weather, for the same. Should be simple to extend the FBHS process a bit.
When a ship has successfully overtaken another, there's the opportunity to maneuver. FBHS has solid maneuvering rules, covering positioning for broadsides, chasers and stern guns, crossing the T, etc, and suggesting how to use ship handling and a bit of piloting skill; players don't need to know about the wind gage or leeward approaches, it's abstracted into fairly simple skill rolls once they decide on a broad strategy.
I'm a big fan of the humble d6 when you need to roll a ton of dice - too many years of Axis & Allies. Batteries of cannons should be resolved with a handful of d6's. Some of the rule sets involve calculating a ton of d20 modifiers and rolling dozens of times for a broadside on the d20 scale. Meanwhile, FBHS has a single die roll for an entire battery, which isn't ideal to me either, so I'll adjust to include chucking handfuls of d6's and adding up hits.
Regardless, the strength of historical buccaneers was their crack shots with the musket, so there need to be adjustments to the combat approach to account for actual historical strategies like picking off helmsman, suppressing gun ports with withering fire, and otherwise clearing the deck with small arms while closing the gap to board. The type of buccaneer ships in the game are typically lightly armed (unlike the 3-4 mast monsters used by pirates in the later age).
There are a number of points at which a merchant ship's reactions (or morale checks) are critical; when spotted (to determine if they lay to, evade, or come about); when they’re overtaken - do they fight or roll over; when they're boarded, do they surrender, defend the decks, or set traps and retreat to closed quarters. Reputation for the buccaneers and pirates will be a factor influencing morale checks.
FBHS has fast, abstract rules for handling the boarding - although, like I mentioned above, the assumption seems to be two heavily armed ships slugging it out with broadsides, movie-style, and not fast rovers raking the decks with small arms and then quickly overwhelming with a boarding action. It also omits grenades, a practical weapon, albeit one you usually don't see in the swashbuckling movies, either. Otherwise, the FBHS rules feature a simple d6 system that would work well with the Axis & Allies style mass d6 rolls.
It'll be important to define some standard ship "types" that make sense to me, by my understanding of the ships of the period; number and types of guns are important, structural hit points, handling ability (for maneuvering), typical crew sizes, and I'll even have to solve the cargo management problem (without having to micro-manage every single item loaded onto the ship).
I plan on yoinking some firearm rules from AD&D's A Mighty Fortress (although I assume the LOTFP gun book will be available long before this campaign is ready) and I'll be scanning Backswords & Bucklers again for ideas as well. I also need to pick up Flashing Blades sometime, I really like the approach in the nautical supplement.
So that's a statement of purpose. More to come.