The Triton-built submersible Limiting Factor is a record-breaking masterpiece of engineering. It has been likened to the Apollo spacecraft, described as the “pathfinder to the last frontier on earth”. It is the first submersible to reach the deepest points of all five oceans and was pressure tested for up to 14,000 metres – a depth that does not exist on earth. Now John Ramsay, chief technology officer at Triton Submarines and Limiting Factor designer, has opened up about the challenges of taking submersible technology to unplumbed depths.
It started with Victor Vescovo, a 53-year-old private equity investor and retired naval officer, who was “a man with a plan” when Ramsay first met him in 2014. In fact, his plan – to become the first person to dive to the deepest points of the world’s oceans in a submersible that did not exist – was a “bit too serious”, Ramsay recalls. “He wanted something just for one person that could get him to the bottom of the five deeps.” And Vescovo was not fussed with frills. “He didn’t want all the specialist requirements of a submarine,” Ramsay says.
To prove the potential possibilities of the machine, Ramsay accompanied Vescovo and Triton president Patrick Lahey on a demonstration dive in the Bahamas. “One of the objectives of that dive was to prove to Victor the importance of being able to see out of the submarine with your own eyes and not just through cameras,” says Ramsay. “We spent a long time discussing the technical details of what was and wasn’t possible, being quite matter of fact about it and admitting when things would take more research, time and money.”
After agreeing to the project, Triton set a loose timeframe for its completion. “We agreed that the best plan was to spend six months working out whether everything was even feasible before we started on a full build project,” Ramsay says. Even when the design stage was complete, Ramsay didn’t take anything for granted. “It’s very easy to design something that can’t be built,” he says. Triton relies on dozens of companies to build integral parts of its submersibles. For Limiting Factor, this included the pressure hull, buoyancy foam and all ten thrusters. “The hardest thing in this process was designing a thing that people could make,” Ramsay says. “With a normal sub, there are usually dozens of companies that can make them, but when you’re doing something like Limiting Factor, that is so extreme and using materials that people aren’t used to, that just isn’t the case.”
The “fundamental objective” of the brief was to design a machine that could “get down there reasonably quickly and is absolutely sure to get back,” Ramsay says. To test whether the grade five titanium hull could withstand the crushing pressure of 11,000 metres deep, Triton headed to the Krylov State Research Centre in St Petersburg. While Ramsay describes the facility as “slightly run down” with “plants growing through the fabric of the building”, the institution is the one place in the world such testing can take place. The procedure saw the pressure hull of Limiting Factor lowered down into the pressure chamber and Ramsay recalls it “scraping down the sides”.
“The pressure hull was designed so that it would fit in the pressure chamber,” he says. “It was absolutely at the limit of what would fit.” A dive of 14,000 metres was then simulated. While this depth is 20% deeper than the deepest point on earth (the Challenger Deep stands at 11,000 metres) it is a requirement for submersibles intending to dive the full ocean depth multiple times. Needless to say, Limiting Factor passed the test, becoming the only submersible in the world certified to dive to 11,000 metres an unlimited number of times.
There have of course been other submersibles that have descended to 11,000 metres. First there was Trieste in 1960 which became the first manned vessel to reach the bottom of the Pacific Ocean’s Challenge Deep, commonly known as the deepest point on earth. Then there was Deepsea Challenger in 2012, which saw Canadian film director James Cameron pilot the second manned dive to the bottom. These were however, according to Five Deeps expedition leader Rob McCullum, “one shot wonders”. Neither of them descended to all five deeps or undertook unlimited dives to 11,000 metres. They both dived to the bottom to the Challenge Deep once, reaching depths of 10,912 metres and 10,908 meters respectively. Limiting Factor meanwhile completed four dives to the bottom and reached a record-breaking deepest point of 10,928 metres.
It was clear from the beginning, Ramsay says, that the brief for Limiting Factor was for an entirely different machine. Unlike the foreboding submarines prevalent in World War Two documentaries, black, cylindrical and sinister, Limiting Factor is “scallop shaped”, more similar to an “axe head” or “wedge”, according to McCullum. This allows it to descend through the water column with ease and reach the bottom quickly – and by “quickly” Ramsay means four hours. High manoeuvrability on the bottom was also crucial to ensure that Vescovo could correct the sub’s position after arriving on the bottom. “It was of the absolute importance to be able to move the sub to the deepest point,” Ramsay says.
There are three viewing ports for visibility, one port per person and a third at the bottom. Each port is encircled with cameras to capture documentary footage and images for an in-progress VR experience. Positioned above the ports is Limiting Factor’s air supply; a rack of oxygen cylinders. The system essentially operates like “a small planet” with carbon dioxide scrubbers absorbing the carbon dioxide. This means that the pilots “keep breathing the same air over and over again,” Ramsay says, and means that Limiting Factor can supply oxygen for an impressive 16 hours, followed by an emergency back-up of 96.
With construction complete, it was time for Limiting Factor to hit the water for sea trials in the Bahamas. Launched from the expedition’s support ship Pressure Drop, Limiting Factor descended for the first time. It was, Ramsay remembers, “a fraught time”. “That point in the project is probably the worst stage,” he says. “The first time it hits the water you know there are going to be dozens and dozens of things that need changing to make it perform as it should.” Vescovo however did not share Ramsay’s anxiety. Emerging from Limiting Factor following his first test dive, Vescovo declared that “going to the five deeps is absolutely going to happen, I’m convinced of that.”
He was right to be convinced. The Five Deeps expedition set new records on each dive, as well as undertaking extracurricular dives on the wreck of the Titanic and the Tonga Trench. Now Triton has its eyes on future projects, including the in-build three-person submersible dedicated to the 182-metre research expedition vessel REV. “The plan is to take what we’ve learned and apply it to new projects,” Ramsay says. “For the REV sub, we’re going to use a lot of the tech that we used for Limiting Factor.” Despite this, REV’s submersible will be capable of diving to 2,300 metres, less than a quarter of Limiting Factor’s capacity. “It does put into perspective how nuts Limiting Factor is,” Ramsay says.