Okay – grab a snack kids and pull up a chair. I have a story to tell about about a really bad dive – the kind of dive you never want to experience again. Hell, the kind of dive you never want to experience in the first place. But it’s at least entertaining, so it might as well be told.
However be warned – it’s a long story, so if that’s not your thing then might I interest you in an audiobook?
Part One – The Why…
Back in 2009 the New England Aquarium (NEAq) was collaborating with Excelerate Energy, who was constructing the Northeast Gateway Deepwater Port for offshore offloading of LNG from thousand foot long tankers. It’s a pretty crazy engineering marvel which you can learn more about it in this link…
This underwater port was being constructed so as not to bring these very large ships into Boston Harbor for offloading – plug in the word “terrorism” and you’ll understand why.
Keep in mind that though the deepwater port system is massive, it lives entirely underwater. It’s comprised of two Submerged Turret Loaders (STL) with flexible gas risers that run down to the seabed, through a manifold distribution system, and then to a buried pipeline that runs to a tank farm on shore.
Each STL is built to hold a 1000′ tanker securely during a CAT4 hurricane (and indeed one has done just that in Louisiana during Katrina back in 2005). Securing each STL are eight anchor rodes, each running for about a mile in length. They start out as a massive wire cable at the bottom of the STL and transition to enormous chain links the size of a Mini. Each rode terminates at a suction anchor some ten stories high and 40′ in diameter.
These STLs are, well, huge – like 40′ tall spacecraft – that hover some 90 below the surface. Crazy!
Check out the link below to get a visual of what a STL looks like, as well as how it’s drawn into the ship to both act as the anchor and the gas offloading point:
Okay – so what does that have to do with me??
Well, NEAq’s role was to see if the deepwater port was effecting the local habitats of several species of dogfish. We wanted to know if the STLs and associated anchor sites (16 in total) acted as a FAD (Fish Aggregation Device), as well as try to determine if the anchor chains, as they slowly, ponderously, churned up the seabed, affected habitats in a detrimental or even positive way.
Researchers from NEAq, WHOI, and elsewhere captured dogfish throughout the spring of 2009 and tagged them with radio transponders. We then deployed four acoustical popup devices in a diamond pattern on the seafloor (at a depth of ~280′) around one of the two STLs, STL B. These devices would record data transmitted from any nearby tagged dogfish and at the end of the summer would be commanded to release from the anchors holding them on the bottom and float to the surface for retrieval.
Prior to deploying them, these acoustical popups were tested in the Aquarium’s Giant Ocean Tank (GOT) and yes, yours truly was in the water with the Principal Investigator (PI) to conduct the tests. Here I am examining the device as it dissolved the link to its anchor.
An acoustical pop-up is a cylindrical pressure housing containing an electronics payload – in this instance data recorders listening for the pings from the tagged dogfish. It a series of floats attached to the top, along with a radio transmitter for RDF locating, and are mounted to a section of railroad rail which is used as an anchor. They are deployed to the sea floor and record data for a given period of time. When it’s time to gather the data off the unit a boat goes out to the site and used a device called the Interrogator to communicate with them. A transducer attached to the Interrogator is lowered over the side, the unique ID of the desired pop-up is entered into the Interrogator and it transmits a series of commands – such as request for battery status, or distance in feet from the unit to the transducer, etc – to the popup. One command instructs the popup to generate a current that will start a chemical reaction that burns off the attachment point to the anchor (as tested in the GOT), thereby allowing the popup to raise to the surface.
During the summer of 2009 I conducted a series of dives on STL B itself – to video aquatic life that may have taken refuge on and around it. Did I mention that the thing is huge? Well, it is. And it just sits there in the water column – the top of it hovering around 90′, the bottom at 140′. On the surface there’s no sign anything is down there, with the single exception of a tiny flag attached to a 5/8″ poly line barely visible floating on the surface. That line then leads into progressively thicker line, still floating, until it finally attaches to a massive Kevlar hawser that then makes a 90 degree turn and runs straight down to the top of the STL. This Kevlar haswer costs $150,000 to replace. Side note – in 2014 a whale watch boat with 160 aboard blundered into this restricted area and sucked part of the hawser into one of her jets. More on that story:
Here’s me sitting on the hawser…
This entire section of ocean is completely off limits to boaters – well, it’s supposed to be!. There’s a 110′ ship, the Gateway Endeavor, whose sole purpose is to patrol the area 24/7/365 a year. For me to dive the area I had to obtain security clearances, develop a very comprehensive dive plan, and present said plan to Excelerate HQ for approval. Additionally all vessels involved in the op needed to have a company observer aboard.
When a 1000′ LNG tanker needs to offload it’s cargo of LNG (re-gassify) it pulls up beside the little flag. The crew then couples the 5/8″ line to a line from inside the bow of the ship and a winch inside the ship begins to draw in the line. Eventually it picks up the Kevlar hawser and then begins to haul up the actual STL until it is completely drawn inside the ship, where hydraulic rams on the ship lock into the STL and the ship and STL become one. BTW – the “Turret” of “Submerged Turret Loader” refers to the section of the STL where the rams lock into it – this section is on bearings and is free to pivot, allowing the ship to watch and rotate due to sea and wind state. A hatch on the top of the STL is opened and the ship’s gas line is plugged in. It takes about five days to full re-gassify the LNG and transfer the ship’s contents to land, and the STL keeps it anchored in place while also providing the gas line.
Here’s a really great animation of how a STL is mated to a LNG tanker:
So I spent some dives following the Kevlar line down into blue (grey) open water to the STL, where I attached a reel to the top of the STL and rappelled down to the underside. So cool! Hanging beneath the STL I recorded video of the huge anchor rode attachments and the massive flexible gas riser – all attached to an alien underwater spacecraft (needless to say, there was no ship on it at the time).
But that’s not the story. That’s just the background. This is the story…
Early fall in 2009, the day came to command the popups to, well, pop up. The Aquarium’s dive boat Lophius (bonus points for what the name refers to) went to the site and researchers used the Interrogator to command release from the anchors. All four units obeyed and responded with a Success ACK.
So the researchers waited – and waited – and guess what? Not a single unit popped to the surface. Nor did the distance between the units and the transducer change, meaning they were still laying on the bottom.
A bottom that is 280 feet down.
The next step was to enlist the use of a ROV to visit the site and the video it returned gave the answer everyone dreaded. The non-crushable floats used, well, crushed at that depth, and therefore had lost their buoyancy. Countless thousands of hours of data was trapped on the seafloor. Priceless data. The ROV didn’t have a grabber – just video. So weeks were spent trying to grapple the units from the surface – to no avail.
During one dive on STL B I asked the PI if we could bring the Interrogator with us, and we did some tests on how closely we could use it to pinpoint the location of one of the four stranded popups.
The results were promising and I felt confident I could get them, but it would require some big dives with a lot of inherent risk – and a special team to pull it off. Several high level meetings later and I was given the green light.
I was going to dive to 280′ in permanent pitch black, onto a featureless sediment bottom, to try to find a needle in a haystack…
Stay tuned for Part 2 of the story, and let me know what you think in the comments.