The DMG, on page 119 has stats for different vehicles. They usually have multiple hundreds of hitpoints. However, isn’t a boat a massive object? If it were, it would be subject to the rules concerning objects: on pages 246-247. The rules for objects state that:
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? If you used a spell to blow a hole into the side of the ship, could you not make it fill up with water and sink? Spells like Meteor Swarm come to mind, on average it’ll 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?