I have a theory about the Final Plunge after a bit of research, it's based from a few theories too, I think the final plunge may have occurred like this:
The water comes to the Boat Deck, and the ship starts to sink much faster than before, still with a 10 degree port list. The 1st funnel's base gets crushed by the water and the funnel falls off to port side, killing a lot of people. As the water reaches the 2nd funnel's base, something inside the funnel explodes, and it falls to starboard side, and a huge black smoke covers the area of the funnel (as described by Jack Thayer). The water touches the area of the 3rd funnel, and the ship is now at 23 degrees, and with the stress caused (as the Titanic reached a angle it wasn't meant to reach, it was too much stress for it), the ship starts to break at the keel (as the keel cannot bend like Banana Peel theory, it's too rigid to do it, but not too rigid to break away), and after the keel breaks, the upper decks immediately break until the lower decks, and the Titanic breaks in half in front of the 3rd funnel, and the 3rd funnel falls off, only the lower decks hold the ship togheter; the forward and aft tower are very weak after the break, and as the bow starts to push the stern with it, the forward and aft tower end up breaking off the ship while the lower decks break off too (the lower decks can't push the stern up), then the stern capsizes to port, and the 4th funnel falls off, then it starts to sink, lifting itself high in the air too, being almost vertical at a certain point, but as there is still lots of air escaping in the stern, it remains afloat for a few seconds and sinks.
I think that makes sense.
