Until today the whole sea was neutral ground. That is over.
From the Salt Bay to the Shell Isles nothing changes: you hunt monsters and enemy ships in peace. But from the Parrot Lagoon onward the game changes. That is where limited combat begins, and only captains within three levels of each other can fight. Each deeper map widens the band by one: four at the Amber Coast, five at the High Mangrove, six at the Basalt Needles.
And then there is Farelhão Bay, where there is no limit at all. Any captain may attack any captain.
Sinking another captain pays skulls, a currency you cannot buy, trade or sell. What it pays depends on the hull you sent to the bottom, not on the level of whoever sailed it, so nobody profits from hunting beginners. Only the first sinking of each captain per day pays, and the one who goes down loses half of what the winner earned.
Skulls climb ten ranks, from Deckhand to Lord of Tides, and they never fall back: spending your balance does not cost you your rank. The skull shop holds the War Frigate, which nothing else can buy.
Whoever arrives in a combat zone, through a portal or setting sail from port, comes in invisible for thirty seconds. But fire once and the mist is gone.
Update: since October 8 there are twenty ranks, they come from captain-combat points and they can fall; skulls are now only a currency. Today, the thirty invisible seconds apply when you arrive in a combat sea; when you set sail from port, the Harbor Mist hides your ship for fifteen seconds.