Ship rulings

Turns

Ship combat takes place on 60 ft hexes. Turns are 6 seconds and all ships act before any characters. Any crew not used may act on their own initiative.

During its turn the ship may designate crew assignments to: oars, sails, bilge, combat and special (using a mounted siege weapon or something similar). At the start of the ship's turn the GM will calculate water taken on. Most ship actions have a numerical crew requirement. Once an action is chosen, the used crew cannot be used until the ship's next turn.

Movement

All ships have a max ocean speed but may exceed these speeds on rivers - if they are river worthy. During combat, speed can only be changed by one hex - i.e. if a ship is traveling at 2 hexes, It can only slow to 1 hex or accelerate to 3 hexes. Turning requires a Water Vehicles check and usually requires some movement prior.

Repair

A character with Water Vehicles, Engineering or Carpenter's Tools proficiency may spend one minute (on their own initiative) to add the ship hull die plus their proficiency modifier to the hull's HP.

Sinking

A ship reduced to 0 hull sinks at the end of its next turn. A ship that exceeds it max cargo capacity sinks at the end of its current turn.

Underwater Combat

When making a melee weapon Attack, a creature that doesn’t have a Swimming speed (either natural or granted by magic) has disadvantage on the Attack roll unless the weapon is a Dagger, Javelin, Shortsword, spear, or Trident. 
A ranged weapon Attack automatically misses a target beyond the weapon’s normal range. Even against a target within normal range, the Attack roll has disadvantage unless the weapon is a crossbow, a net, or a weapon that is Thrown like a Javelin (including a spear, Trident, or dart). Creatures and Objects that are fully immersed in water have Resistance to fire damage