Can a player character grapple a ship?

Question

Background:

The situation contemplates engaging with a huge or gargantuan ship, by means such as an 18th level Rune Knight using the Runic Juggernaut feature as described in Tasha's Cauldron of Everything, pg 46 (also applicable for a large rowboat, in which case a ballista/harpoon as described in Storm King’s Thunder pg 133, similar to an Oaken Bolter’s harpoon attack as described in Mordenkainen's Tome of Foes pg 126).

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Assumption:

I am assuming that a vehicle like a ship is not a creature, as that appears to be dealt with in other questions regarding the effects of spells that target creatures but not objects etc.

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Details:

According to chapter 9 Combat, section Grappling, PHB pg 195, it states (italics mine):

When you want to grab a creature or wrestle with it, you can use the Attack action to make a special melee attack, a grapple. //snip// The target of your grapple must be no more than one size larger than you and must be within your reach. //snip// A grappled creature can use its action to escape.

Further according to Appendix A: Conditions, PHB pg 290 it states (italics mine):

Conditions alter a creature’s capabilities in a variety of ways and can arise as a result of a spell, a class feature, a monster’s attack, or other effect.

According to chapter 9 Combat, section Making an Attack PHB pg 192, it states (italics mine):

1. Choosing a target. Pick a target within your attack’s range: a creature, an object, or a location.

According to Objects section, DMG pg 246, it states:

For the purpose of these rules, an object is a discrete, inanimate item like a window, door, sword, book, table, chair, or stone, not a building or a vehicle that is composed of many other objects.

According to Appendix A: Of Ships and the Sea, section Components, in Ghosts of Saltmarsh (“GoS”) pg 186 states (italics mine):

A ship is composed of different components, each of which comprises multiple objects.

In all the example stat blocks of ships in GoS, despite all of the examples being immune to most condtions, none of them have immunity to the grappled condition (or the restrained condition, for that matter).

According to the description of a Kraken’s Tentacle attack MM pg 197, it states (italics mine):

Melee Weapon Attack: +17 to hit, reach 30 ft., one target. Hit: 20 (3d6 + 10) bludgeoning damage, and the target is grappled (escape DC 18). Until this grapple ends, the target is restrained.

Which is different from a infernal war machine Scavenger’s Grappling Claw, which according to its stat block Descent into Avernus pg 219 it states (italics mine):

Melee Weapon Attack: +10 to hit, reach 15 ft., one target. Hit: The target is grappled (escape DC 12). If the target is a creature, it is restrained until the grapple ends.

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It appears that an attack would (presumably) be targeting the hull component of a ship, either as (the equivalent of) an object, or a location, however it is unclear which.

It also appears that while the rules for grappling in PHB refer to targeting only creatures, the rules elsewhere strongly imply that items other than creatures can be grappled.

It is not clear whether the rules elsewhere (eg. Kraken, Scavenger, harpoon) can only be used by non player characters, or whether a player character wielding a harpoon/ballista against a large (possibly huge?) ship, or a huge Rune Knight against a huge or gargantuan ship, can make use of the grappling rules. Like this.

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Accordingly, can a player character grapple a ship?

Answer 1

They can do something

...but it's probably not a grapple. As cited in the question, the special melee attack available to all players may only be used against creatures. It requires a Strength (Athletics) check contested by either a Strength (Athletics) or Dexterity (Acrobatics) check. Objects do not have Strength and Dexterity scores, and are incapable of making such an opposed check. So are many vehicles, outside of the special rules given in Ghosts of Saltmarsh and Descent into Avernus. It wouldn't be unreasonable for a DM to say their specific rule of having ability scores overrules the general targeting of creatures and makes them a valid target for such contested check, but that would be a ruling in game, and not all vehicles have such ability scores.

Several special attacks such as the Kraken Tentacle and Scavenger's Grappling claw bypass the generic grapple special melee attack by applying the grappled condition to whatever target they hit, and follow the normal attack targeting rules. What exactly this means for an object is not perfectly clear by RAW, but the grappler having a firm grip on the object and dragging it about as if it were an equivalently sized creature would be straightforward enough for me.

The PHB has a relevant section in the introduction on page 8:

Combat is the most structured element of a D&D session, with creatures taking turns to make sure that everyone gets a chance to act. Even in the context of a pitched battle, there's still plenty of opportunity for adventurers to attempt wacky stunts like surfing down a flight of stairs on a shield.

Surfing on a shield is not mentioned anywhere in the combat section with special actions, but it explicitly allowed by the rules. As long as our rune knight has the appropriate grasping appendages, they can certainly try, leaving the DM to adjudicate this. More unusual actions like this are often covered by:

Ability Checks

DMG page 237

An ability check is a test to see whether a character succeeds at a task that he or she had decided to attempt. The Player's Handbook includes examples of what each ability score is used for.

PHB 175

Strength Checks
A Strength check can model any attempt to lift, push, pull, or break something, to force your body through a space, or to otherwise apply brute force to situation.
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Other Strength Checks
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Keep a boulder from rolling

This certainly feels like our Rune Knight is attempting to apply brute force to lift, push, or pull this boat to prevent it from moving. And keeping a boulder from rolling seems like a comparable situation - attempting to immobilize a large object against an opposing force. As always, your mileage may vary between different DMs, but I would say a Strength check sounds appropriate in this situation, with a DC set by the DM based on how difficult they think this task is.

Answer 2

No, the Grapple Special Attack can only be used on creatures.

As you quoted, though the attack action can target an object, the Grapple Special Attack specifically requires the target to be a creature. The other features that grapple, such as the Kraken's Tentacle or the Scavenger's Grappling Claw, allow you to grapple a creature or an object, as they specify you must hit a target, not a creature or object, for the grapple to take effect.
This is an example of Specific beats General. Generally, a grapple can effect a creature or an object. Specifically, the Grapple Special Attack can only be used on a creature.

However, you have made note that vehicles and buildings are not considered objects, as they are made up of many smaller objects. This does not mean they cannot be grappled by, say, a Kraken; it means the grappling creature must choose to grapple a specific object that is comprising the vehicle. The Kraken can grapple the hull, or the mast, or the rudder, but if those parts are broken off of the ship, the grapple ends (though that might have dire consequences for the ship and its crew).