If your structure, also called hull, the inner circle of your ship, reaches zero (0), you will sink. The fastest way to sink a ship is to damage the ship through the back, also called Stern. This tactic is called: "sterncamping".
As soon as the hull hitpoints (integrity) goes down, you will start to loose cannons. Always try to keep your damaged/weakest side away from the enemy. In a scenario where you are helpless, e.a. heavily outnumbered/outgunned, it's better to keep distance. If that isn't possible you can focus on two (2) things:
- Trying to hold out as long as possible. This is a good tactic if you want to buy time for your friends or protect more expensive ships. As a rule, non-Juggernaut Ships, including Ships of the Line, should suicide if they can safe a Juggernaut Ship. This is all due to the high production costs of these ships. The same counts for Fregates when they can safe a Ship of the Line. So don't be selfish here if you sail a cheap Frigate, think about the more common goal. However, sometimes people are in such a position they just can't be saved, keep that in mind.
- Trying to deal as much damage as possible. This is a good tactic if you have a big ship, especially for Juggernaut Ships, since they can't really run or turn to protect their weakest side due to maneuverability.
This information is provided by the update that PotBS Wikia is undergoing, by Captain Vuur.