Watertight doors

[Mary S. Lynn]

We know that the watertight doors were electronically controlled from the bridge. Were they closed before or after the collision? This admitted movie-viewer has seen one version where they were closed immediately after the "Iceberg, right ahead" warning, and one where they were closed after the actual collision. It wouldn't have made any possible difference - just curious. Also - was Thomas Andrews responsible for their only going as high as E deck, and not being topped?

 

[Jeremy Lee]

They were closed AFTER the collision with the iceberg.

 

[Mark Chirnside]

Hi!

Also - was Thomas Andrews responsible for their only going as high as E deck, and not being topped?

Out of interest, that detail has received far more attention that it deserved. 'Topping' off the watertight compartments with a watertight deck has its own problems, especially if there is ever flooding above the watertight deck. Imagine the unbalanced result: water on top, air pockets below. OUch!

Best,

Mark.

 

[Parks Stephenson]

Mary,

Since I'm lazy, I'm going to quote myself:

Lord Pirrie developed the requirements for the design of the Olympic-class liners. Alexander Carlisle, Pirrie's brother-in-law and Chief Naval Architect of the shipyard, turned Pirrie's requirements into a practical design. After Carlisle retired in 1910, Pirrie's nephew, Thomas Andrews, completed Carlisle's work.

Carlisle and Andrews led a team that knew their business. Again, I quote myself:

In the most simplistic terms, the height of two watertight bulkheads is calculated by taking the volume of the compartment that is created between them and assuming that compartment is completely flooded, subtract that volume from the ship's displacement. If the tops of the bulkheads are tall enough to be above the ship's new load-draft line after losing the subject compartment, then water will not rise over the tops. Even if the affected compartment isn't capped by a watertight deck, the bulkheads are still considered to be "watertight," because they can contain the water coming through the opening in the hull within the compartment between them. This is a simplistic summary of the type of calculation that was performed by Titanic's designers when they determined her internal subdivision. Given Titanic's expected operating environment, the height of her bulkheads should have been sufficient. The manner in which a merchant vessel should have been operated meant that the most serious hazard should have been collision with another vessel. Titanic's internal subdivision was well designed for such an eventuality.

Some people essentially assert that Titanic's compartmentalisation should have rivalled that of a warship. That is neither practical nor desirable in a passenger ship design.

Parks

 

[Tom Pappas]

Parks said, "Some people essentially assert that Titanic's compartmentalisation should have rivalled that of a warship."

To which I would add: it is possible to backtrack on virtually any sinking and cite design changes that would have prevented it. The problem is that the resulting structure, although precluding a maritime disaster, would have inevitably created a financial one.

 

[Mary S. Lynn]

I don't know if this is possible mathematically, but how much would the water filling one compartment actually weigh? Would there have been a problem if the same weight were a combination of solid masses instead? (Can you tell that I never went past high school physics)?

 

[Parks Stephenson]

Mary,

Not to sound condescending, but naval architects don't think in terms of how much water weighs inside a hull. As I tried to indicate above, the height of two watertight bulkheads that form a compartment is calculated based on the potential loss in volume of the hull's displacement if that compartment is breached. In other words, we don't talk about the weight of water pulling a ship down (how much does water weigh in water?), but rather in how much bouyancy is lost due to a reduction in the hull's displacement.

Therefore, it doesn't do any good to directly compare the weight of water in air to solid objects in a floating hull. Can you tell me what lies behind your question...maybe I will see another way to help you.

Parks

 

[Mary S. Lynn]

I guess I was just curious about the weight factor. Somewhere in a hazy dream, after a night of feasting on over-priced King Crab and a tantalizing array of rich desserts, I found myself thinking about the possibility of one ton of water in a compartment versus one ton of solid mass. Now, even I know that solid mass won't spill over the top, but if one ton of solid mass were placed in each the first five compartments, as opposed to one ton of water (in addition to what was already there - each reducing volume to its own extent) the ship would not sink. A one-ton anchor would not reduce the volume as much as one ton of water. (Maybe I am getting this?) It's almost like (well, not quite) dropping a 5-ounce feather and a 5-ounce pebble from the top of a building to see which will reach the ground first...different mass and composition. Guess I need to jump into my tub and yell "Eureka" to figure out water displacement! You are not condescending at all, Parks. I am just physics-challenged!

 

[Parks Stephenson]

Mary,

If it helps, think of it this way...a ship floats by displacing water, not by being lighter than water. Solid mass is distributed throughout a ship with full regard for the effect it will have on the ship's ability to displace water (and the effect it will have on trim and a few other factors). Watertight bulkheads are designed to restrict the reduction in buoyancy (and lowering of the hull's load-line) caused by a ruptured compartment to a manageable level. They do not prevent the loss of displacement caused by the rupture, but attempt instead to isolate and restrict free flow of water from high to lower areas of pressure. The volume of the compartment will dictate the height of the bulkheads that form it. Does this help you visualise the situation?

Parks

 

[Charles B. Weeks Jr.]

Mary:
What Parks says is correct. With ships we are always up against one of two limits. Weight, as in displacement or deadweight, and volume as in cubic capacity or registered (Net or Gross) tons. The cross over is the fact that 2240 lbs ( one long ton) of salt water occupies 35 cubic feet of volume. For fresh water its 36 cubic feet. A ship floats because it displaces a volume of water that weights the same as the ship. By the way blimps work the same way. When a ship's hull is punctured and flooding occurs there are to methods of dealing with the change in stability. One is the added weight method the other the lost buoyancy method. The names of these two methods go back to what Parks is talking about, do you lose buoyancy or add weight. Different people use different methods on this question.
Hope that helps a bit.
Regards,
Charlie Weeks

 

[Mary S. Lynn]

Aha! "With ships we are always up against one of two limits. Weight, as in displacement or deadweight, and volume as in cubic capacity or registered tons" My pea-brain is beginning to buzz! (Take cover, now). "Displacement versus deadweight"..that's the answer I was looking for! I sincerely hope that neither of you think I'm a total moron, and I thank you for your explanations. No excuse for my ignorance, other than curiosity.

 

[Charles B. Weeks Jr.]

Mary:
Displacement and Deadweight are both weights, measured in Long Tons (2240 Lbs in USA). The difference between the two is the weight (displacement) of the Light Ship. Light Ship is bare hull, machinery, lifeboats, cargo gear. It is the least the finished ship will ever weight. Full Load Displacement is the weight of the ship with a full load, down to her marks, (that is the Plimsol marks) the most she can ever legally weight. The difference is the Deadweight, ie. carrying capacity.
Regards,
Charlie

 

[Mary S. Lynn]

I guess that the "deadweight" issue is what I finally figured out, Charlie. I used to lurk in a few hulls, and see crate after crate of heavily laden cargo from food to bottled water to T-shirts to store items to concrete mix to books...ad infinitum. (deadweight). I just never mastered the West Indian crew lingo of explanation when I asked about it. I never mastered physics, either! Thanks for a very good exlanation!

 

[Tom Pappas]

Another way to think about displacement weight is to imagine the ship suspended from a spring scale, like in a grocery store. The scale will read the displacement weight. If you then slowly lower the scale, the ship will descend into the water, and its buoyancy will gradually pick up the weight. When it's floating, your scale will read zero: all of the ship's mass is "suspended" by its buoyancy.

 

[Daniel Foerster]

If anyone is interested in the amount of water in the compartments after flooding:

Fore Peak: 800 Tonnes
Hold No. 1: 3000 Tonnes
Hold No. 2: 4500 Tonnes
Hold No. 3: 5300 Tonnes
BR No. 6: 7650 Tonnes
BR No. 5: 8500 Tonnes

To my knowledge Edward Wilding was responsible for the watertight subdivision.