When Mounted On A Ship, Do Siege Weapons Take The Ship's Dexterity Into Account?

Question

Been running a campaign using the ship rules as provided by Ghosts of Saltmarsh, but some confusion recently came up about the ship mounted weapons. While a siege weapon is an object and thus does not take in a creature's dexterity, assuming I am correct about that, is that the same case with a ship's dexterity when the siege weapon is mounted to it?

Answer 1

Siege Weapons have a fixed to-hit number

Siege Weapons work differently than normal ranged weapons. With normal ranged weapons, you get to add your Dexterity bonus to the attack roll. With siege weapons, the to hit is a fixed number that depends on the weapon (p. 255 DMG).

For example, a ballista has the following attack, which requires three actions by operators, one to load, aim and fire each:

Bolt. Ranged Weapon Attack: +6 to hit, range 120/480 ft., one target. Hit: 16 (3d10) piercing damage.

With Vehicle combat for ships in Ghosts of Saltmarsh, what changes is how the weapons get fired -- this now is an action of the ship, for example on page 187 for the Galley:

Fire Ballistas. The galley can fire its ballistas (DMG, ch. 8).

And the Galley's 4 ballistas are referencing the standard ballista from the DMG here. Those ballistas are also listed in the ships stat block again, and have the nearly the same attack action as the normal ballista:

Ranged Weapon Attack: +6 to hit, range 120/480 ft., one target. Hit: 16 (3d10) piercing damage.

The Galley as a ship has Dexterity 4, for a three-point negative modifier. If the Dexterity of the ship would apply to the Ballistas, then the to-hit would need to be three lower than from a normal ballista, for a total of +3 instead of +6. However, the ships ballistas have +6 to hit, like any other ballista. So the ship's dexterity does not factor in the to-hit calculation.

(PS. The ships officer's Take Aim ability grants Advantage to the attack rolls of the ships weapons, but does not change the to-hit roll bonus, either. Thanks to @Kirt)