Vessel Combat

During vessel combat there is an additional layer of initiative called vessel initiative. Pilots roll their vessel initiative at the start of a tactical encounter by making a piloting check. To make a piloting check the player or DM rolls a D20 and adds their proficiency bonus of the pilot and the proficiency bonus of the ship.
While piloting a ship a character may only use the magic action to either attempt a manoeuvre or to power down the helm, or the utilize action to activate a special ability of the ship such as ramming or using a ships unique ability. If a pilot does not attempt a manoeuvre the ship defaults to steady.
Every ship is taking one of four ship manoeuvres: offensive, steady, defensive, and break. All ships enter combat steady. During the pilots activation they use their action to choose a manoeuvre and make a piloting check to succeed, with a DC based on how many opposing ships are in the same combat (not counting any ship currently in break). A pilot automatically succeeds the check if they choose steady. A vessel that is not currently affected by a spelljammer helm, much like an unconscious creature, is incapacitated, but may drift in the last direction it was travelling.

Magic Action Options

Manoeuvres

Offensive. While making an offensive manoeuvre, all siege weapons aboard the vessel gain a +2 bonus to attack rolls, and the pilot may use a bonus action to utilize the ship to ram.
Defensive. While making a defensive manoeuvre, the vessel and any exposed crew on deck gain a +2 bonus to armour class.
Steady. Steady is the ‘default’ of combat manoeuvres, and has no additional effect.
Break. The ship immediately gains one level of break. A ship with one level of break leaves the combat area if all opposing ships have at least one level of break. A ship with two levels of break leaves the combat area if all opposing ships are currently defensive or break. A ship with three levels of break leaves the combat area if all opposing ships are currently steady, defensive, or break. A ship with four levels of break leaves the combat area.
Piloting proficiency checks for break manoeuvres are made at a disadvantage if any opposing vessels have a tactical speed of more than 1 ½ times the vessel attempting to break, or at advantage if the vessel attempting to break has a tactical speed of more than 1 ½ times that of any opposing vessels

Power Down Helm

When a pilot powers down a helm, they immediately gain one level of exhaustion for every 8 hours they have spent on the helm, and the vessel becomes incapacitated.

Utilize Action Options

Ramming

Only ships fitted with rams may be utilized to ram other ships, and only when they are making an offensive manoeuvre. When ramming, the pilot makes an attack roll against a steady, offensive, or defensive ship. The pilot makes the attack roll by making a piloting check.
If the target is also currently offensive, the attack is made with advantage. If the target is defensive, the attack roll is made with disadvantage.
The four types of ram are listed on the table below, with a brief description of their effect.
Bludgeoning. Critical ship shaken, attacking vessel makes a piloting check (DC 15) or takes half damage, both vessels become steady and lose any levels of break.
Piercing. Critical hull holed, attacking vessel makes makes a piloting check (DC 15) or takes half damage, both vessels become steady and lose any levels of break.
Shearing. Critical rigging sheared, both vessels become steady and lose any levels of break.
Grappling. Grappled (piloting check DC 15 to break free), attacking vessel becomes steady and both vessels lose any levels of break.

Unique Ability

Some ships have a unique ability activated by the pilot. This may be the Nautiloid’s ability to teleport to any location known to the pilot, firing the bombard giant cannon of the Great Bombard, or some elven vessels ability to cloak.

Crew Actions

After the pilots turn, each other player aboard their ship takes a turn in regular initiative order. If the pilot has powered down the helm, one of these players may use the help action to get the pilot off the helm, and a different player may use the magic action to take the pilots place and power on the helm becoming the pilot at the start of the ships next turn (the vessel initiative remains unchanged).
Characters and monsters take their turns as normal, but there are several other actions those aboard a ship may take.
Utilize: Siege Weapon. One siege weapon gains an action to either load, aim, or fire (if loaded). Each heavy weapon lists how many actions it takes to load, aim, and fire.
Utilize: Clear Rigging. The vessel loses one level of sheared.
Utilize: Extinguish Fire. The vessel loses one level of fire
Utilize: Repair. The vessel regains Xd6 hit points, where X is the characters’ proficiency score. Cannot be used on creature vessels.
Utilize: Clear Harpoon. The vessel loses one level of harpooned.
Influence: Shanty. The vessel loses X levels of discord, where X is the characters performance skill or proficiency bonus, whichever is higher. If the ship has no levels of discord, the pilot is inspired by their crew and gains heroic inspiration.
Help: Target. One Siege Weapon aboard the vessel gains +2 to it’s next attack roll. This bonus is not cumulative with itself.

Siege Weapons and Critical Hits

Siege Weapons represent an array of magical and mundane devices used to attack ships. The following rules complement or expand upon the rules in the 2024 Dungeon Masters Guide.

Making a Siege Weapon Attack

When making an attack with a Siege Weapon, a creature rolls a d20 and adds their proficiency bonus, plus the bonus for the vessel role and hull class, the attack bonus of the siege weapon, and any bonus for the current maneuvre. A siege weapon may be used to attack a creature, but always attacks at disadvantage unless the creature is Gargantuan.
Each siege weapon deals an amount of damage of the type listed. Siege weapons may cause additional effects when they critically hit (on top of the standard critical hit rules).
Siege weapons ignore a vessels damage threshold.

Critical Effects

When a creature scores a critical hit with a Siege Weapon and the target is a vessel or a ship, the target ship gains X levels of Discord where X is the total bonus to the successful attack roll, and the attacker rolls on the Critical Effect table below.
While a vessel has any levels of Discord, its Pilot makes all Magic Actions at disadvantage, and each Utilize Siege Weapon action requires a successful proficiency check at DC 10 + X, where X is every level of Discord. Certain other rules such as ramming and other unique abilities may also cause Critical Effects.

*reroll this effect if the target is a creature ship.
Hull Holed. Treat all damage dice as if they had rolled maximum. The ship cannot make a water landing until it has been fully repaired, and will begin taking on any liquid it is submerged in.
Deck Crew Hit. A random creature on the deck of the ship is hit by the attack. Roll damage for the creature separately, and do not double the damage dice as they were not critically hit.
Siege Weapon Damaged. A random Siege Weapon is hit by the attack. Roll damage for the Siege Weapon separately, and do not double the damage dice as it was not critically hit.
Fire. The ship gains X levels of Fire, where X is the total bonus to the successful attack roll. At the start of its activation a ship takes 4d6 Fire damage for every level of Fire.
Ship Shaken. Every creature aboard the ship except the pilot must make a DC15 Dexterity saving throw. On a failure, they are Stunned until the end of their next activation.
Rigging Sheared. The ship gains X levels of Sheared, where X is the total bonus to the successful attack roll. A ship has 1- to its AC for every level of Sheared, and while it has any levels of Sheared its Pilot makes all rolls at disadvantage.
Interior Crew Hit. A random creature inside the ship is hit by the attack. Roll damage for the creature separately, and do not double the damage dice as they were not critically hit.
Spelljammer Shock. The pilot immediately gains the Unconscious condition and two levels of Exhaustion. They then start a short rest, at the end of which the Unconscious condition ends on them.

Harpooning

Some siege weapons apply one or more levels of Harpooned. While a vessel has one or more levels of Harpooned it loses all levels of Break and becomes Steady, and cannot attempt a Break manoeuvre.

Towing

A vessel may tow any vessel up to two hull classes larger. The towed vessel must be attacked by some secure means such as ropes, cables, or chains, and must not have an active spelljammer helm. Towed creature vessels must be unconscious, and may pose a hazard should they awaken.
Towing a ship of two hull classes smaller or less incurs a 15% speed penalty at tactical speed. Towing a ship one hull class smaller incurs a 25% speed penalty at tactical speed. Towing a ship of equal size or one hull class larger incurs a 50% speed penalty at tactical speed and a 25% speed penalty at cruising speed. Towing a ship of two hull classes larger incurs a 75% speed penalty at tactical speed, and 50% speed penalty at cruising speed.
A ship may not tow a vessel more than two hull classes larger than itself without additional assistance from secondary vessels. For each secondary ship of equal hull class to the primary vessel, treat the primary ship as one size larger for the purposes of towing.
When a battleship or dreadnought tows a vessel of a hull class smaller than itself, treat the towing ship as if it were one hull class smaller.