Death in the Depths

Titan Submersible

The loss of the Titan submersible along with the five people aboard has been in the news this week. They were going down to look at the Titanic. There hasn't been much in the way of detail, so I thought I'd chime in.

A pint's a pound, the world around. A cubic foot of water holds eight gallons and a gallon holds eight pints, so a cubic foot of water weighs 64 pounds. A square foot is 144 square inches, so a column of water one foot high with a square cross section of one inch will weigh about half a pound. The Titanic is lying at a depth of 12,500 feet (roughly two and a half miles straight down from the surface). To determine how much pressure there is at that depth, you multiply 12,500 (the depth in feet) by one half (the weight of one foot of water) and you get 6,250 pounds or about three tons of pressure per square inch. Since the surface of Titan is thousands of square inches, the total pressure pushing in this little bubble of air is like zillions of tons.

Some people have pointed out that carbon fiber was used in the construction of the submersible, and noted that carbon fiber is very strong in tension and is almost useless in compression. So while carbon fiber may have been used in construction of the submersible, there must have been some other material included in the mix that does have good strength in compression. Concrete, steel or aluminum would all be valid choices. James Cameron used steel in his submersible.

Forging the steel pilot sphere for Deepsea Challenger
James Cameron took it to the bottom of the Mariana Trench,
which is three times deeper than the Titanic