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.
For more information: Broadside, Bow, Stern, Damage, PvP Guide.
This information is provided by the update that PotBS Wikia is undergoing, by Captain Vuur.