Combat

The Order of Combat

Like creature combat, ship combat is organized into turns and rounds. Initiative is rolled for each ship, and the creatures on that ship all act on their ship's turn. Independent creatures like sea monsters or characters that are not on a ship roll their own initiative.

Sailing is slow, and weapons take time to reload, but these rules are designed to be fast and fun. For the purposes of rules and action economy, a round of combat represents 6 seconds in the game world, though 30 seconds to 1 minute is a more thematic representation.

Combat Round Step by Step

Captain Phase. Captains choose their ship's actions, and they may roll to Push the Crew.
Initiative. Declare any Lookouts. Lookouts (or Captains) roll initiative.
Take turns. Each ship takes a turn in initiative order. On a ship's turn, characters may go in any order they see fit. Each may choose an Action Station based on the Captain's chosen actions, and they may choose a different station each turn. They may also choose another action like casting a spell. Ships and characters may Ready actions to trigger anytime before the ship's next turn.
Begin the next round. Repeat the steps until the combat is over.

Captain's Phase

During this phase, each ship's Captain decides what actions the ship will take. Each ship has a set number of Action Points and the Captain can spend any of these to assign actions for the characters and crew on board to carry out later in the turn. Any actions not carried out by the other characters will be rolled by the Captain.

Push the Crew

During a time of need the Captain may decide to push the crew to their limits. If the Captain makes a successful Intimidation or Persuasion check, the ship gains one extra action point this turn but loses one action point next turn. A Captain cannot Push the Crew if they succeeded in doing so the previous round.

Initiative Phase

Initiative is rerolled each round of combat. After all Captains have decided their ships' actions for the turn, each ship rolls a d20 and adds its DEX modifier. This roll is made by the Captain unless the ship has a Lookout. See the section on Action Stations.

A Ship's Turn

On a ship's turn, the Pilot or Captain may move a distance up to the ship's speed and make two rotations. The characters may take any actions that the Captain chose at the beginning of the round, plus any other actions like the Bosun's Raise Morale ability or casting a spell. After the characters have gone, the Captain rolls for any actions the characters didn't take. These actions may be taken before, after, or at any point along the ship's movement. Characters may also Ready actions (i.e. wait for a target to be in range).

Arc of Fire

In the age of gunpowder weapons, most ships carried the majority of their arsenal along the side of the ship, requiring the vessel to maneuver to the sides for most cannons to have a shot, requiring them to turn to hit a target they were chasing. Broadside refers to this area. Other attacks, like the 1st Rate's Chase Guns, can only fire Fore & Aft.

Ramming

A ship may attempt to Ram another ship. At the beginning of the turn, the Captain may spend all of the ship's Action Points to declare a ram. On the ship's turn, if it ends its movement with its bow adjacent to another ship's space it may attempt to ram. Both ships roll a die equal to their base hit die. The ramming ship adds +1 to its roll for each space it traveled this turn. The winning ship deals damage to the losing ship as though it had just dealt a critical hit with its primary attack.

Example: A brigantine (7d10+14 hp) rams into a sloop (6d8+6 hp). The brigantine travels 3 spaces before making contact. It will roll 1d10+3 versus the sloop's 1d8. If the brigantine wins it will deal critical hit damage (2d10+3) to the sloop.

If for some reason the ramming ship cannot get to a space adjacent to another ship, it does not ram and its Action Points are lost.

Boarding & Close Combat

After ships are close enough to engage in close combat or creature scale combat, DMs are encouraged to switch to a 5ft square grid maps. Mass combat and Mob combat rules can be used to deal with the crew, but, like any good story, it's the heroes and not the extras that matter!

References

5e - Supplemental - Limithron's Guide to Naval Combat.pdf