Page 119 of the DMG has stats for airborne and waterborne vehicles. They usually have multiple hundreds of hit points.
[...] That said, one torch can burn a Huge tapestry, and an earthquake spell can reduce a colossus to rubble. You can track a Huge or Gargantuan object's hit points if you like, or you can simply decide how long the object can withstand whatever weapon or force is acting against it. If you track hit points for the object, divide it into Large or smaller sections, and track each section's hit points separately. Destroying one of those sections could ruin the entire object. For example, a Gargantuan statue of a human might topple over when one of its Large legs is reduced to 0 hit points.
So would a ship not work similarly?
Does a ship sink only when it reaches 0 HP?
The counterargument is the one about smaller sections of a massive object; if a giant hole is made in the hull of a ship, one that’s too big to patch up, then surely it will sink.
If a ship has HP and AC, does it count as a creature for the use of spells?
Plenty of spells in D&D 5e don’t damage objects: fireballs and lightning bolts only light objects on fire, so would a ship count as a creature?
Can you target a specific sub-section of a ship? And how would damage thresholds interact with that?
This is linked to question 1. Could a mage casting a powerful spell, or someone wielding a siege weapon, etc., actually aim for a sensitive point on a ship, and destroy that one sub-section?
Furthermore, does a subsection maintain the damage threshold of the full structure? Warships, for example, have of DT of 20, and the stats for resilient objects show that most large objects have less than 30 HP. Does this mean that either, you do nothing to the object, or you nearly destroy it?
My reason for asking this is that spells like meteor swarm, on average, do around 160 damage (I believe it also applies to objects). This isn’t enough to destroy most ships (fair enough, the blast is too small), but surely it could destroy enough of the hull to sink most vessels, no?