The Obsidian Wave

The Obsidian Wave
Vehicle (water), legendary
Carved from a single, massive piece of volcanic glass and reinforced with dark magic, The Obsidian Wave is a terrifying sight on—and beneath—the waves.
Properties
Submersible: The Obsidian Wave can seal its decks and submerge completely, traveling underwater at a speed of 40 feet per round. It can sustain its crew with breathable air for up to 72 hours while submerged.
Stealth: The dark glass of the hull makes the ship incredibly difficult to spot at night or in deep water. Wisdom (Perception) checks made to spot the ship have disadvantage.
Weapons: The ship is equipped with four heavy ballistae and a forward-facing ramming prow that deals 8d10 bludgeoning damage to ships or large creatures it strikes.