A ships boilers are great targets when you actually nail em, usually kills all propulsion and ship can sink Titanic style (albeit the forecastle is what gets lifted into the air) with a single hit (really helps too when the boilers are adjacent to powder magazines).
Really rough waters and no more working propulsion ended up with a quick sinking with only 1 hit (waters were only ~90 meters deep so was able to check her out once she bottomed)
