How to run a sea battle

[Darth Credence]

My current campaign has taken a turn towards the ocean, and it looks like there will have to be a battle between two ships, and then a battle with some sort of sea monsters. I have never run anything on a ship before, so I was wondering if anyone had some tips on how to best proceed.

The setup is that the players are on a pirate ship, and need a particular person in order to open a tomb on an island. This person is on a different ship, so they will need to attack it at sea and capture the person, then get away. They are both pirate ships, so it will be an evenly matched battle in terms of overall crew. The players are level 10, the opposing pirate captain is a blackguard and he has an evoker and a couple of assassins as high level crew, while all the rest of the pirates on both ships are just reskinned bandits.

I have no idea how they are going to approach this (for that matter, they could always go find a different person in the same family to fulfill the needs, so this all may be moot). They may try to sneak on at night, attack the other ship and grab him during the battle, negotiate for him to be turned over, or something else. But assuming they go for attack and grab during a battle, does anyone have any experience in running a ship to ship battle? I don't want that to be the focus unless the players do, but I would like some structure to it.

Thanks for any help you can give.

[Emongnome777]

I don't have access to it right now, but Ghosts of Saltmarsh has rules of running a ship and I think some about battles between ships (though maybe not so much on crew actions?). Anyway, if you don't have access to GoS, here (https://media.wizards.com/2018/dnd/downloads/UA_ShipsSea.pdf)'s the UA (don't know what changed from UA to published). The published also had ship drawings, which the UA doesn't have.

Wish I could help more, I've never ran a sea combat before, but I do plan on doing so in the campaign I'm running.

[PhantomSoul]

Not strictly about the combat aspect (I haven't tested that part, though there are some guidelines), but this has been a great starting point for seafaring: https://drive.google.com/file/d/1JxObgcSWyA3vnlclSg7DhrrbTUoZksdq/view. Taking Spelljammer as a launching point could also work well! (I haven't played, but I've head appealing little tidbits from mechanics videos.)

[Darth Credence]

Outstanding! Thank you both for the info - there's a lot of good stuff in there that I think will give me what I need.
I'll post how everything goes to share what in this works well and what I screwed up on.

[Spiritchaser]

Think about the party and make sure everyone has something to do.

Assuming, as you suggest, that your players opt for a frontal assault rather than tailing their foe and finding a way to sneak on board at night, you’ll have two groups at range for a while

Now, at level 10, your party might be quite mobile, but it’s certainly possible that you’ll have a few dedicated melee types getting bored while the spell sniper goes nuts.

Do the ships have any weapons? Having a siege weapon lobbing balls of flaming pitch will give some characters the critical job of keeping things from burning down as well as attacking the other ship.

Can the opponents magically transport a small team across, possibly summoning something scary for the party to fight, while putting out fires, trying to burn the sails on the other ship and steering a course through rocks?

Make sure the players are calling the shots, not along for the ride and that the tactics are the party’s to control.

Are they going to cripple the foe from afar, or close and board? Maybe they have the means to fly an away team over? If they’re captaining the ship this is a no brainer, if not did a way to cede command to the players.

Make the rules of movement clear

Whatever rules you use for ship movement they are unlikely to be something you use much. How detailed you want to get is up to you but but make sure you go over how it’ll work in your game with your players (do you want different speeds at different headings? Different abilities to point upwind on differently rigged ships, different turning rates? or just, your ship has a speed and no-one goes within x degrees of straight upwind?) keep it simple or make it fancy, make sure everyone knows how it’s going to work.

[Garimeth]

Lots of good resources and responses. ESPECIALLY making sure everyone has something to do. Couple of notes:

The world has magic, both sides have magic.

Prestidigitation lets you put out fires, decide how big you will let those fires be.

Counterspell is the most important thing a caster brings, not fireball. The side with the more counterspells wins - naval magic combat is rocket tag. Fog cloud obscures vision, landing a fog cloud, silence, or darkness on the other ship's deck is massively debilitating.

Bombarbs and Ballistae massively outrange spells. Pirates know this, if they were bad at being pirates, they would be dead pirates. They will attempt to disable other vessels before closing. You are not pulling to within 120 ft range of any ship that looks remotely capable of putting up a fight or escaping.

TBH, their best bet is either sneaking on at night or teleporting (DDoor) a strikeforce onto the enemy deck. If most of your party is melee, then try and turn the naval action into a boarding action as soon as possible.

I DM for an ocean heavy campaign with IRL Sailors and Marines, so we get a little... in the weeds with our Naval stuff.

[ImproperJustice]

It will seem a little out there but Stars Without Number, revised edition has some really great rules for ship to ship combat where everyone is placed in departments like Captain, Gunnery, Navigation, and Damage control.
Each section provides benefits to the other wIth the captain allocating resources.
The Captain can also trade devastating blows to the ship by allowing the GM to create emergencies in a section. These require some dramatic direct action by the crew to resolve quickly or they can lead to massive loss of that section, personel, etc...

Now, what’s great is that these rules are OSR / D&D 1e based and easily fit 5e rules. And it doesn’t take much imagination to change futuristic ship names to naval ship names.
IE Comms can be helm/ lookout, navigation is the rigging/helm, etc.


And what is left is a very dynamic ship combat system that our group likes to use that involves everyone.

And best part is SWN is free.

[prototype00]

Oh, be aware if any of your characters has Control Water (Druids and Tempest Clerics) as that is basically an “I WIN” button for naval combat.

Specifically this:

Part Water: You cause water in the area to move apart and create a Trench. The Trench extends across the spell's area, and the separated water forms a wall to either side. The Trench remains until the spell ends or you choose a different Effect. The water then slowly fills in the Trench over the course of the next round until the normal water level is restored.

Thats a trench 100ft cube that opens instantly. Open it under the front half of a ship and it will flip, fall 100ft and capsize.

Then you just dismiss the spell and fill the trench with water over 6s. Is that enough for any sailor to save himself? Dubious.

Edit: Oh, even better, switch the effect to “Whirlpool” targeting the bottom of the trench. Then the water will flow back in over 6s (you dismissed the trench effect) while any sailors have to swim against the giant whirlpool sucking them even further down to Davy Jones’ Locker. Them as survived the 10d6 fall damage that is.

[Darth Credence]

Thanks for all the help and suggestions. In the end, the players found out what port the ship was heading to, and set up an ambush on the dock for when they got off. I will file away everyone's recommendations here for if I ever end up with sea battles in the future.

[Rule-Of-Three]

I DM for an ocean heavy campaign with IRL Sailors and Marines, so we get a little... in the weeds with our Naval stuff.

So do your players also have interest in trying to find a way to hide inside an extra-dimensional space with Rope Trick, get it above the prize, and then fast rope into a VBSS? Do they argue over how fast a compartment floods, assuming a DCFN with two months fleet time did the hatch maintenance? Lol.

You're not alone, my friend. Swashbuckling campaigns are amazing, assuming everyone is on the same page and geeky about things nautical and naval. I've run them in multiple engines, and I still think West End Games Star Wars did it best so far. I've used Gazatteer Kingdom of Irendi rules, Ships and the Sea, Spelljammer, 7th Sea, and my own homebrew for steampunk airship combat, and the main takeaway I have to offer the OP is make sure your players want chewy naval engagements before trying to create a tactical simulation of naval combat. If it's half or mostly no, then stick to the narrative formats recommended in modules like Stormwrack. Otherwise, you'll find out that calculating turn radius and relative bearing to target to calculate fire arcs sucks the fun out of the session amazingly fast for people that aren't into it.

[Rule-Of-Three]

Oh, be aware if any of your characters has Control Water (Druids and Tempest Clerics) as that is basically an “I WIN” button for naval combat.

Specifically this:

Part Water: You cause water in the area to move apart and create a Trench. The Trench extends across the spell's area, and the separated water forms a wall to either side. The Trench remains until the spell ends or you choose a different Effect. The water then slowly fills in the Trench over the course of the next round until the normal water level is restored.

Thats a trench 100ft cube that opens instantly. Open it under the front half of a ship and it will flip, fall 100ft and capsize.

Then you just dismiss the spell and fill the trench with water over 6s. Is that enough for any sailor to save himself? Dubious.


I appreciate where you're going with this, there are anti-carrier torpedoes out there that operate by vaporizing a large amount of water under the keel, disrupting displacement and snapping the ship. It also drops into the void created by the blast, and then quickly subsumed. Trick is, these torpedoes use a low yield nuclear warhead.

Take a look at 100 cubic feet sometimes. It's roughly the size of a porta-potty. That's not going to cause anything larger than a skiff to capsize, assuming you time the displacement right immediately following the cresting of a wave while porpoising. You're right that characters that control the underwater engagement zone are 3D combatants against a 2D target, but humble spells like warp wood and create bonfire are plenty deadly enough.

[Darth Credence]

I appreciate where you're going with this, there are anti-carrier torpedoes out there that operate by vaporizing a large amount of water under the keel, disrupting displacement and snapping the ship. It also drops into the void created by the blast, and then quickly subsumed. Trick is, these torpedoes use a low yield nuclear warhead.

Take a look at 100 cubic feet sometimes. It's roughly the size of a porta-potty. That's not going to cause anything larger than a skiff to capsize, assuming you time the displacement right immediately following the cresting of a wave while porpoising. You're right that characters that control the underwater engagement zone are 3D combatants against a 2D target, but humble spells like warp wood and create bonfire are plenty deadly enough.

The control water spell is not 100 cubic feet. It is a cube up to 100 feet per side, or a maximum of 1,000,000 cubic feet.

[Rule-Of-Three]

The control water spell is not 100 cubic feet. It is a cube up to 100 feet per side, or a maximum of 1,000,000 cubic feet.

Ah, got it. Reading error. Yes, that would be significantly more impactful.

Funny once you start getting nautical in theme, you quickly get nautical in tactics. A single competent caster is enough to sink a vessel if they get within range. A caster that can find the target and cast this spell is a figurative Exocet. So in a high magic world, over-the-horizon strike, detection, and evasion (teleport, flight, divination) C5I principles, interdiction, and countermeasures (counterspell, dispel magic, control flames, etc.) become essential to just giving the Marines a chance to board. Two ships with equally skilled casters would be a wonderful cat-and-mouse reenactment of Master and Commander, as whomever got the drop on the other would have tremendous advantage.

I find that mid to high-level casters usually break nautical encounters in a way the makes not casters feel like sidekicks, and tend to run swashbuckling campaigns in lower magic worlds as a result. The other option is when the ships themselves are magical or have a magical helm (Spelljammer) that requires caster control. In those cases, I incorporate Seamanship skill (varies in edition) to execute maneuvers (i.e. change course by 90 degrees in 75% of the move distance as normal), and make the Leadership feat and high CHA scores relevant for how your crew executes the orders. The caster then gets to play a Captain mini-game that is tactically relevant and contributes to the whole, without making the party a caster tactical nuke delivery vehicle.

[Garimeth]

So do your players also have interest in trying to find a way to hide inside an extra-dimensional space with Rope Trick, get it above the prize, and then fast rope into a VBSS? Do they argue over how fast a compartment floods, assuming a DCFN with two months fleet time did the hatch maintenance? Lol.

You're not alone, my friend. Swashbuckling campaigns are amazing, assuming everyone is on the same page and geeky about things nautical and naval. I've run them in multiple engines, and I still think West End Games Star Wars did it best so far. I've used Gazatteer Kingdom of Irendi rules, Ships and the Sea, Spelljammer, 7th Sea, and my own homebrew for steampunk airship combat, and the main takeaway I have to offer the OP is make sure your players want chewy naval engagements before trying to create a tactical simulation of naval combat. If it's half or mostly no, then stick to the narrative formats recommended in modules like Stormwrack. Otherwise, you'll find out that calculating turn radius and relative bearing to target to calculate fire arcs sucks the fun out of the session amazingly fast for people that aren't into it.

Lol, sorry for the late response. That kind of stuff 100% happened in the 3.5 game I ran from Stormwrack material, but as you mentioned in another post, EVERYONE was on board, so it was fun.

New game, in a lower magic setting... lol. Well now the party is a retired USMC CWO2 that was in the other game in 2013, me an FMF sailor, a prior Counterintel Marine, a GMC, a prior army Cav scout and a civilian paramedic.

The prior soldier and the paramedic get bored fast if I let the others take too long. They are good sports, but I definitely had to have them make a chain of command that they will follow to prevent everyone from arguing about tactics after initiative is rolled lol.

Fortunately the non casters of the group rolled characters that can contribute meaningfully in a ship engagement through skills and bonus actions while controlling the vessel or its weapon systems, and the three people that mostly do that are the two prior marines and the gunner's mate so it works out.

When the paramedic and soldier were initially talking about broadsides and stuff we had a very lengthy out of game discussion about what magical Naval tactics would ACTUALLY look like. We decided that independent steaming for warships was probably rare unless they had casters, and that most others would use flanking maneuvers and the superior range of their bombards (much further than most spells, just with disadvantage) to disable the other vessels before approaching if the goal was piracy or violence.

Related, I have not run 7th Sea yet... but I REALLY want to use its rules for a Norse Viking based game with a swashbuckling feel. think, the Odyssey meets Count of Monte Cristo, but Vikings. We'll see. So many games, not enough time.

[Garimeth]

Lol, sorry for the late response. That kind of stuff 100% happened in the 3.5 game I ran from Stormwrack material, but as you mentioned in another post, EVERYONE was on board, so it was fun.

New game, in a lower magic setting... lol. Well now the party is a retired USMC CWO2 that was in the other game in 2013, me an FMF sailor, a prior Counterintel Marine, a GMC, a prior army Cav scout and a civilian paramedic.

The prior soldier and the paramedic get bored fast if I let the others take too long. They are good sports, but I definitely had to have them make a chain of command that they will follow to prevent everyone from arguing about tactics after initiative is rolled lol.

Fortunately the non casters of the group rolled characters that can contribute meaningfully in a ship engagement through skills and bonus actions while controlling the vessel or its weapon systems, and the three people that mostly do that are the two prior marines and the gunner's mate so it works out.

When the paramedic and soldier were initially talking about broadsides and stuff we had a very lengthy out of game discussion about what magical Naval tactics would ACTUALLY look like. We decided that independent steaming for warships was probably rare unless they had casters, and that most others would use flanking maneuvers and the superior range of their bombards (much further than most spells, just with disadvantage) to disable the other vessels before approaching if the goal was piracy or violence.

Related, I have not run 7th Sea yet... but I REALLY want to use its rules for a Norse Viking based game with a swashbuckling feel. think, the Odyssey meets Count of Monte Cristo, but Vikings. We'll see. So many games, not enough time.

EDIT: Worth mentioning too that one of the casters is a storm sorc, so it really changed the discussions about points of sail, at least for the PCs.