Investigators say it could take them up to 18 months to determine why Titan imploded. Photo / AP
Until the Titan disaster June 18, no one had ever died while piloting or riding a submersible on deep dives. This remarkable safety record stood for nearly a century.
Federal investigators say it could take them up to 18 months to determine why Titan imploded during its dive to the Titanic wreckage, killing its five passengers. But engineers interviewed by The New York Times pointed out possible weak points in the sub’s design.
Titan’s owner, OceanGate, took a unique approach with the vessel, working to minimise costly overhead. The lightweight craft was relatively easy to transport. It required no dedicated mother ship, but instead could be towed behind a rented ship. Compared with rivals, the company said, the savings made Titan “more financially viable.”
Titan had several cost-saving departures from proven submersible designs. What follows is a comparison of Titan’s design with a standard vehicle that, in typical fashion, relies on conservative engineering rules that have proved themselves over many decades.
Unlike most other submersibles, Titan’s hull was shaped like a pill, which fit more passengers. (A sphere has been the industry standard, known to be better suited for deep-sea pressures.) The hull’s central cylinder used carbon fibre, not the more expensive titanium used in other submersibles. And Titan’s carbon fibre cylinder was attached to titanium hemispheres, creating several joints of dissimilar materials that are challenging to bond properly.
Submersibles must withstand the deep ocean’s crushing pressures, which squeeze with equal force from all sides. At Titanic’s depth — 3.8km down — every square inch of a submersible experiences three tons of force.
A spherical hull distributes the stress evenly, making it the best shape for resisting the compressive forces of the abyss. Any other shape, experts said, will tend to deform unevenly.
Unlike Titan, Alvin, a research submersible, has an all-titanium hull. Since 1973, it has completed more than 4,500 dives.
The pressure applied to a pill shape is distributed disproportionately and may cause collapse similar to a soda can being crushed.
A spherical shape allows for a uniform distribution of pressure, making it less susceptible to distortion.
Titan’s hull was larger and held two more passengers than Alvin, which fits three. In three years of dives, OceanGate charged up to US$250,000 ($405,000) per person to visit the Titanic.
Tim Foecke, a retired forensic metallurgist who has done mechanical testing and failure analysis on metals and carbon fibre, said the change in hull geometry from a tight sphere to a lengthy tube may have contributed to Titan’s catastrophic failure. A larger hull needs to be stronger and thicker to withstand the same pressure as a smaller one. In two hulls of the same thickness, he said, the larger one would “collapse or buckle” first.
Most deep-sea craft undergo costly rounds of inspection and testing by reputable marine organisations that specialise in certifying the deep-diving craft as safe. But OceanGate CEO Stockton Rush obtained no certification for Titan, saying it stifled innovation. In a documentary, he said: “You are remembered for the rules you break, and I’ve broken some rules to make this. The carbon fibre and titanium — there’s a rule you don’t do that. Well, I did.”
Kedar Kirane, a mechanical engineer with expertise in damage, fracture and fatigue in fibre-reinforced composites, said if he were designing the Titan, his top priorities would be testing and certification.
“I would probably emphasise the actual testing itself because that’s very critical,” he said. “Safety is at stake, so before actually using it in a real-world application, I would make sure it passes all the certification required and a lot of experiments.”
The engineers who were interviewed also expressed design concerns over areas of Titan where dissimilar materials were joined. Because different materials change shape at different rates when under pressure, achieving and maintaining a seal in these areas can be challenging.
Titan’s hull was designed so that a carbon fibre shell was glued to titanium rings on either end.
Under deep-sea pressures, carbon fibre would compress in diameter more quickly than the titanium, placing stress on the glue joint.
The dissimilar materials used in the craft’s hull construction, said Alfred S. McLaren, a retired Navy submariner and president emeritus of the Explorers Club of New York City, “have different coefficients of expansion and compression, and that works against keeping a watertight bond.”
Moisture or sea salt could have degraded the hull’s carbon fibre and the glue joining it to the titanium, creating another potential weak point, said Kedar Kirane, a mechanical engineer with expertise in damage, fracture and fatigue in fibre-reinforced composites. Foecke also said that the acrylic of the viewport might have failed where it met the titanium or that uneven tightening of the hatch bolts might have caused uneven stresses along the porthole, causing a fracture.
The best way of outwitting the many dangers, the experts agreed, would have been to subject Titan to rigorous testing under the anticipated conditions and stresses. Fatigue of various materials also would have had to be considered and continually monitored. Manufacturing defects or any damage could build up over time as the Titan endured the cycles of stress associated with repeatedly going down miles to the bottom of the Atlantic and back.
A detailed timeline stretching back to 2013 shows OceanGate did extensive developmental work and testing for Titan. Still, left out of the public record are any proprietary tricks and improvements that OceanGate may have made as it gained field experience with its experimental sub.
OceanGate created most of Titan’s hull out of carbon fibre, rather than the conventional titanium used for Alvin. Experts said the risky design saved money.
Titanium is strong against both compression and tension. That means it can withstand forces that are crushing it or pulling it apart. Carbon fibre, though, is much more effective in resisting pulling forces than crushing forces, such as compression. It resists pulling for a while before breaking, but collapses or buckles if pushed on or compressed.
“I was very surprised” by the fibre construction of Titan, Foecke said.
Carbon fibre is strong and lightweight. It reduced Titan’s weight to 9,525kg, compared with Alvin’s 20,410kg.
“This weight reduction allows us to carry a significantly greater payload,” Rush said in a company news release last year. Rush was serving as Titan’s pilot when it imploded.
To further cut costs for the 2023 season, Rush rented a mother ship that was smaller, older and less expensive than those on previous expeditions. Called the Polar Prince, it was too small and cramped to carry Titan on its deck. The ship thus towed the lightweight craft on the three-day voyage from St. John’s, Newfoundland, to the Titanic site.
“I thought the sub and platform were being tossed around pretty roughly,” recalled Arnie Weissmann, the editor-in-chief of Travel Weekly, about his expedition in May with the same mother ship. In contrast, Alvin travels to its dive sites aboard a dedicated mother ship with custom winches, hangars and a machine shop. A crane places it into the ocean.
Asked if towing Titan risked damage, in addition to other questions, a company spokesperson, Andrew Von Kerens, said: “OceanGate is unable to provide any additional information at this time.”
As a class, submarines go down for days, weeks and months. They operate autonomously. In contrast, submersibles go down for hours and rely on a mother ship for such things as crew sustenance, communications, sleeping bunks and proper toilets. The combination of a support ship and the undersea craft can be costly. Recently, a pair went up for sale at US$50 million.
SOURCES: Tim Foecke, former director of the Center for Automotive Lightweighting at the National Institute of Standards and Technology; Kedar Kirane, assistant professor, Department of Mechanical Engineering, Stony Brook University; Arun Shukla, co-director, National Institute of Undersea Vehicle Technology, Department of Mechanical, Industrial and Systems Engineering, University of Rhode Island; Woods Hole Oceanographic Institution. NOTE: Alvin is a U.S. Navy vessel that is operated by Woods Hole with funding from the National Science Foundation.
This article originally appeared in The New York Times.
Written by: Helmuth Rosales, William J. Broad, Eleanor Lutz and Bedel Saget
Photographs by: The New York Times
©2023 THE NEW YORK TIMES
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