Adventuring at sea can be simple or more complicated, depending on what you enjoy in your game. If you want to move the party easily from one area to another, you can have a professional crew in a stalwart vessel do the heavy lifting. You can also hire that cantankerous, one-eyed salt with the questionable dinghy to take them up river, all with a little narrative flair, but with little interaction with the environment. Or you can make things riskier by rolling some dice and letting fate take a hand at the tiller.
The current rules in 5e are very light on what happens on and in the water. Below are some optional rules that shouldn’t add too much complexity while still imparting more interest from being surrounded or submerged in water.
Ship Combat
The aim of this blog isn’t to produce a mini-game with complex rules, but to flesh out the existing combat rules in order to enliven sea battles. Most of what’s below codifies some missing elements in the rules as written or adds some level of verisimilitude and player choice.
Maneuvering. Ships move forward or aft, have momentum, and unless under constant propulsion, slow quickly to move with the flow of the water. Once a ship’s motive power is lost, it it loses 10 ft. of speed per round until coming to a stop relative to the current. The ship table below shows average speeds for common ship types. Smaller vessels should be able to turn 90° within two boat lengths of beginning a hard turn. Large ships may take up to four boat lengths.
Damaging Ships. Ships can take damage like anything else, but the effects can have drastically different results. The ship table below shows the armor class and hit points for various components, along with a damage threshold for the hull. The ship’s hp are reduced only if the damage is above the damage threshold. Ship damage has the following effects, based on the component. The only conditions that can affect ships are grappled, invisible, and restrained. They are immune to poison and psychic damage. All of the components have +7 to Strength, -2 to Dexterity, and +5 to Constitution saving throws and ability checks. Ships automatically fail all Intelligence, Wisdom, and Charisma saving throws.
- When the hull is reduced to half its hp, the ship’s speed is halved and it begins taking on water. One quarter of the crew need to work on damage control or the ship begins sinking. If the required crew are not executing damage control, the ship’s speed is reduced to 0 after an hour and one hour later, the ship sinks. When the hull is reduced to 0 hp, the ship’s speed is reduced to 0 and if one half of the crew does not execute damage control, the ship sinks one hour later.
- When the helm hp is reduced to half, the ship cannot turn unless two crewmembers spend one minute and succeed on a DC 15 Strength ability check. Each time the helm takes damage after this, control is lost again and the DC of the check is increased by 1 after each successful attack. Once the helm is reduced to 0 hp, the ship cannot be controlled until two crewmembers spend time repairing the damage.
- When the sails’ hp is reduced to half, the ship’s speed is halved for movement relying on the sails. When the sails are reduced to 0 hp, the ship’s movement is reduced to 0 for movement relying on the sails.
- When the oars’ hp is reduced to half, the ship’s speed is reduced to half for movement relying on rowing. When the oars are reduced to 0 hp, the ship’s movement is reduced to 0 for movement relying on rowing. Most ships carry extra oars and this is reflected in the oars’ hp and rapid ability to replace oars.
Ship Weapons. Ships can have mounted weapons and the attacks from individual combatants aboard the ship. For ease of use, the average ship’s weapon has the following characteristics. These large weapons take up a five-foot square, can fire every other round, and require two crew members to use. There are other, more powerful weapons, some with magical properties, that can deliver more damage and/or other effects.
Armor Class 15, Hit Points 50, Ranged Weapon Attack: +6 to hit, range 120/480 ft., one target. Hit: 16 (3d10) piercing damage.
Ramming. Ships can use their movement to inflict damage if they run into another ship or large creature. While the ships are maneuvering, if the ramming captain can succeed on a contested Intelligence ability check by 5, the ramming ship can be in a position to ram its target. If the ramming ship does not have a naval ram, it delivers an amount of bludgeoning damage equal to the speed (in feet) x 1d4 and the ramming ship’s hull takes half of that damage. If the ramming ship is equipped with a naval ram, it uses a d6 instead of a d4 and only takes one quarter of the damage to its ram and hull. The naval ram has AC 14, 50 hp, and a damage threshold of 10. Once it is reduced to 0 hp, the ship acts as if it does not have a naval ram. After a ram, the ships are locked together for at least 1 minute. The only way to move away during combat is to concentrate rowers on backing off for more than one minute. Since rams are below the water, they are resistant to fire damage. It’s possible for a ship to have a ram enhanced by magic that delivers more damage or some other effect.
Repair. With the exception of special damage control, ship’s damage can only be repaired by a concentrated effort, with the roll coming at the end of each day. The amount of damage that can be repaired each day is equal to 1d6 + 3. If the ship is in a port capable of repairing ships, this roll can be made three times per day. Each roll costs 20 gp for supplies, plus 5 gp for the port repair costs.
Fire Damage. Some weapons and attacks can affect the ship in different ways. If a fire attack exceeds the damage threshold and the component fails a DC 15 Dexterity save, the component is on fire. If a component is on fire, it takes 1d10 fire damage without having to pass the damage threshold and must succeed on another DC 15 Dexterity save or add an extra 1d10 fire damage. This reflects the ability of the fire to spread. Fire can spread in a reasonable manner between components if the adjacent component fails a save, but oars are resistant to fire damage and have advantage on saves vs. catching fire.
| Vessel Type | Dinghy | Sailing boat | Longship | Sailing Ship |
| Length | 10 ft. | 45 ft. | 80 ft. | 150 ft. |
| Beam | 5 ft. | 10 ft. | 20 ft. | 40 ft. |
| Crew | 1 | 1 | 40-80 | 60-200 |
| Passengers | 2-5 | 3-10 | 10-30 | 20-200 |
| Speed: Sail | 0 | 3 mph/25 ft. | 5 mph/45 ft. | 5 mph/45 ft. |
| Speed: Oar | 3 mph/15 ft. | 3 mph/20 ft. | 5 mph/20 ft. | 0 |
| Hull AC/hp(dt) | 11/50(0) | 15/100(10) | 15/300(15) | 15/300(15) |
| Helm AC/hp | See Oars | 12/50 | 16/50 | 18/50 |
| Oar AC/hp | 12/25 | 12/100 | 12/100 | None |
| Sail AC/hp | None | 12/100 | 12/100 | 12/100 |
Movement Aboard Ships
Ships are usually crowded, with gear and crew all over. The area is considered difficult terrain.
Sea State. When the ship is heaving in heavy seas, anyone who takes a full move and does not use an action to hold onto a part of the ship must succeed on a DC 10 Dexterity saving throw or fall prone on the deck. If the total is 1 or less, the creature falls overboard if it isn’t secured with a rope or something similar. If the ship is also in a violent storm, the DC is 15.
Fighting Aboard Ships
In order to more accurately portray the crowded press of combatants, two medium or small creatures can occupy the same space. All attacks thus joined are at disadvantage, as are all Dexterity saving throws by the combatants.
Crew vs. Crew. In order to simulate the large press of a chaotic battle, determine the conditions and support of the various sides and roll on the table below at the end of each round. Modify the roll under the following conditions.
- The enemy captain has been obviously defeated: +10
- The PCs are displaying unusual powers or great might: +5
- The friendly crew outnumber the enemy crew: +1 for every 10 more fighters
- The enemy crew outnumbers the friendly crew: +1 for every 10 more fighters
- The friendly captain has been obviously defeated: -10
| 1d20 | Effect |
| 1 | The friendly crew loses 5 morale points and the enemy crew gains 3 morale points |
| 2-4 | The friendly crew loses 3 morale points and the enemy crew gains 1 morale points |
| 5-7 | The friendly crew loses 3 morale points |
| 8-13 | The struggle is hot and close, surging back and forth. |
| 14-16 | The enemy crew loses 3 morale points |
| 17-19 | The enemy crew loses 3 morale points and the friendly crew gains 1 morale points |
| 20 | The enemy crew loses 5 morale points and the friendly crew gains 3 morale points |
Morale. Determine the morale of the crews prior to combat. An average crew will have a morale of 10. This can be affected by various conditions prior to the battle. For example, if the ship has been at sea for an extended period, they might have a lower morale, or perhaps have come off a successful attack and have a higher morale. There could also be conditional aspects to the morale, such has one side having a large number of ranged attackers in the rigging, firing on the enemy crew. Once the crew’s morale reaches 0, they surrender.
Casualties. Based on the rolls above, the crew takes a percentage of casualties (killed or wounded) equal to half the morale points lost.
Off the Ship and in the Water
If a creature falls into the water, new challenges arise. Use some of the mechanics below to add some spice to getting wet.
Perception. If the creature has no swim speed and is trying to discern something that requires visual acuity underwater (writing, facial features, etc.), Wisdom (Perception) ability checks are at disadvantage.
The following table shows how far creatures can discern objects that are underwater. If the observer is above water, the distances are halved.
| Conditions | Visibility |
| Clear water, bright light | 60 ft. |
| Clear water, dim light | 30 ft. |
| Murky water or no light | 10 ft. |
Swimming with no armor or light armor. Characters without a swimming speed must expend 2 feet of movement to move one foot. Rough water acts as rough terrain.
Swimming with medium armor. Characters without a swimming speed must expend 2 feet of movement to move one foot. Rough water acts as rough terrain. Further, you must expend half of your movement to keep from sinking 10 feet on your turn.
Swimming with heavy armor. Characters without a swimming speed must expend 2 feet of movement to move one foot. Rough water acts as rough terrain. Further, you must expend a full move to keep from sinking 10 feet on your turn.
Swimming while holding a shield. Characters without a swimming speed that have donned a shield move at half speed.
Swimming long distances. After each hour of swimming, covering a distance of one mile in calm water or half a mile in rough water, a character without a swim speed must succeed on a DC 10 Constitution saving throw or gain one level of exhaustion. Characters in heavy armor make this roll at disadvantage.
Melee Attacks in the water. A character without a swim speed makes all melee attacks at disadvantage unless using a dagger, javelin, shortsword, spear, or trident.
Ranged Weapon Attacks in water. A ranged weapon beyond normal range attack automatically misses. 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). Attacks from water to air or vice versa are at disadvantage regardless of the weapon type.
Casting Spells Underwater. If a character who cannot breathe underwater casts a spell that has a verbal component, they are not holding their breath. After the spell is cast, they have a number of rounds equal to their Constitution modifier (minimum of one) before they start suffocating.
This brings a close to the Serpent Lake series; be sure to check out parts One and Two and let us know your thoughts on campaigns that heavily feature ship travel in the comments or on Discord!