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Underwater disasters show the price of design flaws, arrogance

Jul 22, 2023

On 10 April 1963 the USS Thresher (SSN-593), a nuclear-powered submarine, sank 220 miles off the coast of Cape Cod with 129 aboard. My father’s cousin, George Ronald Kroner, a 21-year-old sailor, was among them. That was 60 years ago this past April. There was not much in the news to commemorate the event. Coincidentally, my father played a minor role in the submarine redesign (more on that later).

This past Father’s Day, June 18, the submersible Titan was lost on a dive to explore the Titanic. All five aboard perished.

Both vessels imploded from the weight of water above them. Similarities between the two events ends there. The Thresher was a submarine that can travel independently, whereas the Titan was a submersible requiring a surface ship.

Thresher was undergoing sea trials after maintenance at the Portsmouth Naval shipyard in Maine. One part of the sea trials was to go to its maximum rated test depth of 1,300 feet. The Thresher had been to this depth about 40 times since her initial sea trials in 1961.

Thresher Cmdr. Wes Harvey stopped at 400 feet to check for leaks, and then he reported to the surface ship “at one-half test depth.” The next communication was “minus 300 feet” or 1,000 feet. Although accounts vary, the next communications included “experiencing minor problem” and “have position up angle” and “attempting to blow”, meaning that the sub was attempting to return to the surface by blowing its ballast tanks.

Next there was a garbled message, “test depth” with the possibility of the preceding word “exceeding.” At any rate, the Thresher was gone under 8,400 feet of water and resting on the ocean floor. The crush depth would be about 1,950 feet based on the Navy’s 1.5 safety factor, but the actual implosion may not have occurred until about 2,400 feet.

The Titan submersible made about 12 dives down to the Titanic to a depth of about 12,500 feet, almost 10 times the test depth of the Thresher. Each 2.3 feet of water height equals 1 psi pressure, so 12,500 feet is 5,400 psi.

What caused the Thresher accident? Here is the probable series of events, in my estimation. First there was a very small water pipe leak onto an electric panel, causing loss of communications and loss of electric motor propulsion. I suspect this is the “experiencing minor problem” mentioned above. Normally a submarine surfaces by aiming upwards and powering up by electric motor propeller. But since this was disabled, the backup plan was to blow the ballast, which was attempted per the communication “attempting to blow.”

Why didn’t this work? Compressed air is injected in to the ballast tank to replace water, but a screen was designed into the compressed air line. As the compressed air pressure lowered when released from its reservoir, it became colder, which is a basic law of thermodynamics. This colder air caused moisture in the line to freeze onto the screen blocking the air flow. Also, the lower the sub, the harder and slower it is to blow the ballast.

Now what can be done? Unfortunately, there is no Plan C.

With the Titan, there are many red flags regarding safety. The hull is reportedly made of carbon fibers and titanium. Carbon fibers are very strong in tension, but the hull under water is in compression, so it would be like trying to push with a rope. Presumably resins used with the carbon fibers provided lateral support of the carbon fibers. The rated depth has been changed several times, so it doesn’t seem to be a firm number. The design has never been approved by any regulatory agency or built to any national standards and calculations and the design is not available for review. What factor of safety is being used?

The Titan had a signal warning in case of a hull crack. To me this is more a notice of impending death than a warning.

Here is more about my father’s role in the Thresher redesign.

This is my father’s account. He was a technical writer and his company was hired to write a section of the submarine manual concerning flexible pipe joints, presumable bellows and braid type. He and a photographer and an engineer from Westinghouse drove from Pittsburgh to somewhere in New Jersey where the flex joints are made. The manual needed details about how to properly install, inspect, maintain and test these flex joints.

Engineering is critical to safety on anything where consequences of failure can result in death or severe injury, such as submarines and submersibles where there is no room for error. For Titan it was arrogance and a total disregard for safety. For Thresher it was an innocent mistake of designing a screen into the compressed air line in spite of a culture of safety.

The importance of design and safety reviews cannot be underestimated. The more critical eyes the better to catch seemingly small but important things that might slip through the cracks.

Equally important is adherence to national engineering standards including design, testing, inspections and approvals.

At the end of the day, engineering failures doomed both the Titan and the Thresher.

Ed Sokalski, a Salisbury Township resident, is a retired mechanical engineer.

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