This set of rules was shared with me by one of my fellow players in Arise & Descend. When they aren’t playing in our near-weekly game they also DM. Recently they noticed a gap in rules for naval warfare. Unlike Ghosts of Saltmarsh, this rule set is for when the party are on other vessels in a fleet or when the story may demand that the group zoom out from the single ship to a small conflict between two fleets.

Dave, not me, my friend, asked if I would share these for feedback. I have edited for copy, but have not playtested these rules.

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On Ships and Naval Battles

A Naval System for 5th edition Dungeons & Dragons

By Dave

Tall ships on the sea are a great setting for a D&D campaign. The romance of the high seas has driven stories for centuries, and finding adventure there can spice up any campaign.

I have a homebrew campaign running, and in it my players have gotten themselves involved in a civil war on an island nation. Of course, any war like this is going to involve some pretty intense naval battles that I wanted my players to take part in.

However, when I looked into rules and systems for running naval battles, there wasn’t anything that really worked for what I wanted. There is some really fun stuff in the Unearthed Arcana “Of Ships and Sea,” which was refined for the Ghosts of Saltmarsh adventure. Those are great if you’re running a full on naval campaign, with all sorts of rules for maintaining a crew and a ship over long periods of time. 

What I couldn’t find, though, is something for a major set piece battle to conclude my players current story arc. So I’ve come up with some rules and a system for running a naval battle that I think could be useful to other DMs looking to change up their player’s experience.

One quick note at the top: This system assumes your PCs will be on the ships, and that the players themselves will make decisions for those ships. Story-wise, this creates a bit of a problem. Either your players are in command of the ships they’re on or your players are controlling an NPC instead of their own character. If you’re like me, and you’ve always wondered why Han Solo was given the rank of General when he’s done nothing to qualify for that rank, the former is a bit hard to swallow. But some players won’t like the way the immersion is broken for the latter. It’s a small wrinkle, but it’s still there, and you might want to address it with your players.

Preparation and Ship Stat Blocks

Rather than playing as a character, each player will take over a ship. Each ship will have a stat block which will include Strength, Dexterity, and Constitution scores. Wisdom, Intelligence, and Charisma scores will all be zero. Ships are also immune to most effects, because they’re… ya know… ships. They are vulnerable to fire attacks. 

Strength will relate to the amount of damage each attack can cause. The modifiers for various attacks will be based on this score. You add some flavor to this by giving a bonus to a STR score to a ship with a veteren crew, or a penalty to a ship with lots of novice or pressed sailors who aren’t as motivated.

Dexterity will relate to ship movement and speed. A ship’s base speed is 300 feet, adjusted for 50 feet per Dex modifier. For example: A ship with a 14 Dexterity (+2) should have 400 feet of movement. Ships get -3 to their Dexterity score for each size above large.

Constitution works similarly, but will relate to ship AC and hull HP. The base hull HP is 100, adjusted by 10 HP per Con modifier. For example: A ship with a 16 Constitution should have 130 HP. Ships should get +3 to their Constitution for each size above large.

On top of hull HP, each ship will have a number of crew members. Max crew number should be equal to the length of the ship. A large ship (100 feet long) will have a max crew of 100, whereas a gargantuan ship (200 feet long) will have a max crew of 200.

Max crew is in relation to the number of actions a ship can take.  A ship can carry more than its max crew, but cannot take anymore actions because of it.  For example, if a ship with a max crew of 100 gains 30 more crew after sinking another ship, putting it’s total at 130, it still can only take four actions.   

Ships get one action per 25 crew members per turn, rounded down. For example, a ship with 100 crew members gets four actions per turn. But as they lose crew members, they lose the manpower to do as much. So once they go below 100 crew members, they only get 3 actions. A ship with 25 or fewer crew members cannot attack. They can only change course, make repairs, or tend the wounded.  

• Note: When building your stat blocks, make sure to pay attention to how each ship is balanced. Perhaps a flagship of the fleet has 200 crew members, meaning it gets eight actions. But such a large ship is ungainly and probably has half the movement of a smaller ship. You might even consider saying changing course on a ship that size takes two actions.

The ship’s actions are as follows

• Change Course, Drop, or Raise Anchor:  Ship changes to a different heading, drops anchor to stop, or raises anchor to get under way. 
• Arrow volley – Ranged Weapon Attack: + STR to hit. reach 150/400 ft., one target. Hit 2d10 + STR crew. 
• Ballistae – Ranged Weapon Attack: + STR to hit. reach 200/500 ft., one target. Hit 2d12 + STR piercing damage to hull HP.
• Take Cover – Crew members are ordered to take cover. Arrow volley damage (crew casualties) is halved.
• Repair damage – Crew members repair their damaged hull. Heal 1d10 + CON hull HP.
• Tend the wounded – Crew members give medical treatment to their fallen crew members, allowing them to return to the fight. Replace 1d8 + CON crew.
• Grapple and board – When a ship moves within 50 feet of another, they can attempt to grapple and board. The attacking ship will roll a Strength check +1 for every 10 crew members rounding down contested by a Constitution save +1 for every 10 crew members rounding down. The boarded ship can choose to fail this save. Once the two ships are grappled together, they are both restrained.

After including all the actions, a ship’s stat block should look like this

When a ship’s hull HP drops to zero, the ship sinks. Any ship that enters the space in which a ship sank may pick up the remaining crew members. All crew members will be rescued. If an ally of the sunk ship moves into the space they add all the crew members to their current crew. If an enemy ship moves into that space they add half the crew members to their crew. 

This is because sailors don’t want to drown and know that if they try to fight the ship rescuing them, they will be left behind. Half the surviving crew members will join the fight in the new ship because they’re either pressed or sailors for hire therefore sailing for one ship or another is all the same to them. The other half will willingly go below decks as prisoners as that’s preferable to drowning.

Setting up Battle

The battlemap for these engagements should be a grid on primarily open sea, though some islands or a coastline can certainly add some tactical flavor. One square on the grid should equal 50 feet. Since ships are large and slow-moving objects in a large area, each round is equivalent to about 6 minutes. Ships will be sized to 50 foot squares.

• Medium = 50 feet long (a large yacht)
• Large = 100 feet long (a sloop or a brig)
• Huge = 150 feet long (galleon or a schooner)
• Gargantuan = 200+ feet long (frigate or Ship of the Line)

Movement

When it comes to sailing ships, the wind is an important factor. A token should be placed on the map to indicate the direction of the wind. A ship may not sail directly into the wind, but can sail at a 45 degree angle towards the wind. Ships sail fastest going perpendicular to the wind, so when they head 90 degrees from the wind, they have full movement. Sailing away from the wind is the slowest, so ships headed the same direction as the wind have one-third speed, rounded to the nearest 50 feet. Quartering the wind (45 degree angle in any direction towards or away from the wind) will give ships two-thirds speed rounded to the nearest 50 feet.

In practice, it should look as follows. The diagram below is for a ship with 300 ft of movement:

It takes one action to change course or drop anchor to stop, but if no action is taken to correct course, the ship will spend it’s full available movement each turn continuing in the same direction.

If a ship’s movement will lead it to hit another ship or some other obstacle, it must use one of its actions to change course or stop.

A ship cannot attack through an allied ship’s space, but must move to a space with a clear shot at its target if it wants to take an attack action.

Boarding Rules

Of course, no high seas adventure would be complete without the chance to board another ship. As an action, a ship within 50 feet of another can take the Grapple and Board actions. If that action is successful, the two ships are tied together and restrained. While two ships are grappled and restrained, they attack each other. Each ship gets one action for each 25 crew members rounding down per round.  They can attack or retreat and break free. 

• Attack: +1 for each 10 crew members rounding down. Damage 1d10+1 for each 10 crew members rounding down.
• Retreat: Strength check +1 for every 10 crew members rounding down contested by a Constitution save +1 for every 10 crew members rounding down. The enemy ship can choose to fail this save.

Once one ship has less than half crew, the rest of the crew will surrender. If a ship already is down to half a crew, it will surrender as soon as it is grappled. The winning ship has two options:

• Bring captured crew aboard their own ship, adding half of the surviving crew of the captured ship to their crew member total (and taking the other half prisoner), and scuttling the captured ship.
• Add half the surviving crew of the captured ship to the crew member total (taking the other half prisoner) then split the new crew total evenly to take command of both ships.

If your entire party is on a single ship, or if more than one of your player’s ships grapple on to a single enemy, you might want to replace this grapple roll with a full encounter and ship-based battlemap.

Adding Your Player’s Traits

Most of these ships will be pretty similar in capabilities. But you can add some variation to these fights by giving bonuses based on your players’ character classes and traits. Story-wise, your player’s heroes will have spent some time with the crew members of their ship teaching them some new skills and talents, which gives those crews certain advantages in battle.

For example, in my campaign, I have four PCs, a Barbarian, a Paladin, a Ranger, and a Wizard. For my final battle, I will have them all on separate ships (which each player will control), and give the following bonuses:

• Barbarian: He’s great at close quarters combat so his ship will have advantage on his Grapple and Board Strength check and +5 to his boarding attack.
• Paladin: She’s a healer and a tank so her ship will be resistant to Arrow Volley (she loses half the crew members per volley, down to a quarter with the Take Cover action), and she has a +5 to her Tend Wounded action.
• Ranger: She’s a classic ranged fighter so her ship will have no range disadvantage for her Arrow Volley or Ballistae actions, and get a +5 to her Arrow Volley damage.
• Wizard: He loves to cast Expeditious Retreat on himself and keep moving in battle so his ship will have an extra 150 feet of movement, and he can add fire damage to his Ballistae action.

You should add your own bonuses based on the personality and favorite tactics of your characters. 

Final Notes

Another big change you could add to this is adding cannons, assuming you’re playing with the Firearms rules. Since I don’t use them in my campaign, I didn’t think too hard on how they would work. But that doesn’t mean you couldn’t adapt this for Firearms rules.

An optional rule you might use is to add changes to the wind direction.  If you want to use this, choose a random interval (or roll for one) such as 3 rounds or 15 minutes (real time), and roll either a d4 or d8 to choose a random change in wind direction.

And finally, this is all pretty complicated, and might be a bit much to throw at a party in one session. I would advise bringing these concepts slowly. For example, put your players on a single ship that you control, and give them each one of the ship’s actions to use as they see fit. Then you can slowly bring in concepts like wind direction, movement, or boarding one at a time, so that by the time your players reach their climactic battle, they are comfortable with all these rules and the tools at their disposal.

Hopefully this can give you a framework to build an epic and memorable naval battle to your campaign. If you have any thoughts or suggestions for improvements to this, I’d love to hear them.