I'm no expert... still learning
I will try and explain my thoughts about the effect on the sinking process with WT doors being opened
Forgive me if I point-out the obvious.
A ship will sink if it is heavier than the amount of water it displaces. Consequently we do not overload a ship!
A ship will also sink if the force of buoyancy keeping it above the surface of the sea is removed.
In simple terms:
If we add weight to a ship and keep adding it, it will sink.
If we remove buoyancy and keep removing it, the ship will sink.
Titanic sank by a combination of these two processes .
First, the puncturing of holds 1 and 2 and boiler rooms 6 and 5 caused her to lose buoyancy. i.e. extra weight was not added to the ship to make her sink. The forepeak tank was holed as well but it was full of water beforehand so once again no added weight!
Thus, the ship intially lost buoyancy and in doing so sank by the head. This continued until the water level reached the top of the Collission Bilkhead.. the first bulkhead after the bow...WT Bulkhead 'A'.
As soon as it did so, the water poured over the top and, because the ship was tilted by the head, poured forward and over the bulkhead into the empty storage compartments above the Forepeak tank. This caused the bow to sink a little more. However this second part of the sinking process was due to the added weight of water not to the original loss of buoyancy.
While this was happening, the ship was still loosing buoyancy and would continue to do so until every compartment open to the sea was full.( A little simplified but sufficient for our purpose!) Leaving all the WT Doors open:
If all the WT doors were left open, the ship would become one entire compartment open to the sea and the sinking process would be one of continuous los of buoyancy.
The water would flow from its source.. the hull punctures.. and make its way right to the stern.
In this way, the loss of buoyancy would have been more evenly distributed along the entire length of the ship. There would be no more added weight and she would settle in the water until the entire bouyancy was lost.
However, more to the point, I do not think the hull would have fractured!
Leaving the WT doors open would have allowed the ship to settle evenly. The loss of buoyancy would have been at a steady rate. Consequently, this might just have prevented the hull from fracturing thus the moment of sinking might have been delayed for a very brief time
However, the rate of loss of buoyancy was relentless and when the amount of buoyancy needed to keep Titanic afloat was all used up then it was all over.
Next: Leaving all the WT Doors closed:
If all the WT doors had been left closed then Titanic would have lost buoyancy in 4 compartments.. Nos 1 & 2 holds and Nos 6 & 5 Boiler Rooms.
These would have to be filled before water poured into the successive compartments astern of them. Thereafter. the sinking process became one of added weight rather than lost buoyancy. The length of time the ship remained above the surface would depend on the rate of filling each intact compartment and this would finish when the amount of water equal to the total volume of Lost buoyancy plus added weight of water was greater than the weight of the amount she displaced before the accident. 48,300 Tons? or 1,690,500 Cubic feet of sea water. Partial closure of the WT Doors:
(The actual situation when Titanic sank)
We know that the WT doors forward of Boiler Room 4 were closed and that there was a small amount of water coming into the forward bunker in Boiler room 5. This means that buoyancy was being lost in all comparments forward of Boiler Room 4.
Because the water was entering 5 slower than 6, the water level in 6 was rising faster in there and finally overtopped the WT bulkhead between 5 and 6. While this was happening, the water level in the forward bunker of number 5 had been rising. Eventually the bunker doors collapsed under the pressure and the combined flooding would be free to move aft toward the WT Bulkhead between 4 & 5. Because the WT door between these compartments was close, it would then have to rise up that bulkhead before it gained access to Boiler Room 4.
As I pointed out earlier, all the sinkage up until the water reached that level was due to loss of buoyancy. This being the case, The center of gravity did not move from it's original place. However, the Center of Buoyancy would most certainly have moved amd the Center of Gravity would have tried to follow it. The result was a complicated series of stresses which caused the hull to fail at it's weakest point.
A fracture below the waterline, allowed extra sea water to pour into the main engine room and travel forward and aft through the open WT doors. This sudden influx of water caused the hull to sink bodily. What is more, it returned the sinking process from one of gaining weight to once more, one of losing buoyancy. Weight was no longer being added to the hull from water entering a sealed compartment.
Because the WT doors at the aft end of the engine room were open and thereafter, open to the end of the shaft tunnels, the water very quickly went aft and the stern lost buoyancy in a complicated sequence. This agravated the bending moment and the stern section bent back level with the sea.
Perhaps if the WT doors been closed at the aft end of the Main engine room, it is just possible that there would have been enough retained buoyancy in the stern section when it broke free of the forward section.
Perhaps some of those on the stern section might have lasted long enough to be saved.
Here's another poser:
If the lights stayed on until the last moment; where did the power come from? The generators needed steam and steam came from boilers. This means there must have been a supply of steam to the main or emergency generators right up until a few moments before the end.
Sam Halpern wrote an article "Why a low Angle Break" In it, he showed a sketch of Titanic with a waterline right up to the masthead light and extending aft to meet the sea at the last WT Bulkhead.
Sam's water line shows the engine rooms and boiler rooms completely inudated. If this was the final waterline, where did the steam come from to light the masthead light and the rest of the ship?
If there was enough electric power to serve all the ships lights then the steam to generate it had to come from Boiler Rooms 2 or 3 because the 5 single end boilers in Boiler Room 1 had never been lit and the Boiler Rooms forward of No.3 were flooded
It follows that the length of Titanic's keel above the surface of the sea must have been much greater at the time when the lights went out. I have made crude modifications to Sam's sketch and included suggested water lines as the sinking progressed.
However here's another mystery:
Although not shown, if Wilder's assumed down flooding of 1600 tons in the first 40 minutes is correct, then Titanic' forward draft would only have increased by 9.3 inches and her aft draft decreased by the same amount.