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Name: Christina
Status: other
Grade: other
Location: NJ 
Country: N/A
Date: 1/4/2006


Question:
In relation to the large amount of pressure on each side of a submarine when submerged, the closer to the ocean floor a submarine goes, the stronger the pressure. What is allowing the submarine itself not to become crushed or concave?


Replies:
Your understanding of water pressure is correct. If a submarine dives too deep it will be crushed.

Roughly speaking, a submarine is rated for three types of diving depths. There is the normal operating depth, a safe excursion depth, and then the"crush depth."

Bob Erck


Christina,

Naval attack submarines must be built with great structural strength to be able to withstand the enormous pressures at the depths they use for tactical purposes. This is one reason for the cylindrical shape of submarines as cylindrical shapes are best for withstanding high pressures. The reason for that is the external pressure puts the shell of the submarine under straight compression, which the steel is best able to withstand. If the sub had large flat areas, the pressure could bend the metal relatively easily.

Nonetheless all submarines have a maximum depth; if they venture below that depth, the hull is in great danger of being crushed. The maximum depth for modern naval submarines is 800 to 900 feet; I do not believe any naval attack submarine can go below a depth of 1,000 feet with safety.

For every 10 meters (32.8 feet) increased depth in water the pressure increases by one atmosphere (about 15 lb/foot^2). That is about 2160 pounds per square foot (2160 lb/ft^2) or about 1 ton per square foot. At a depth of 1,000 feet, the pressure increases to 450 lb/inch^2 or 30 tons/foot^2.

Research submarines can go much deeper. The record I have found is "Alvin" which is owned and operated by the Woods Hole Oceanographic Institution. This has a maximum operating depth of 4500 meters (14,764 feet)! The pressure there is around 450 atmospheres (6750 lb/inches^2 or 450 tons/foot^2). Remarkable!

The short answer to your question is that submarines are engineered and constructed to withstand the pressure up to their maximum operating depth.

Best, Dick Plano,
Professor of Physics emeritus, Rutgers University



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