What it Takes to Deploy an OBS
We completed 44 OBS deployments during this cruise. Usually, when we hear over the radio that we’re nearing the deployment site, we put on our safety gear, walk to the deck, and begin the operation. A couple of intense moments. Then we wait. First for the OBS to reach the bottom, then for the survey to finish. This is about three- hours of wait. Once that’s done, we’re free to rest or do whatever we want until we reach the next location. (So, it’s movie time😊😊. I’m kidding.) That’s the drama on stage. Then there is a group of people behind the curtain. Now, it’s time to see what they do behind the spotlight; what it really takes to have each OBS ready for us to deploy at every location. First, I directed the question to Mark, the captain of the R/V Marcus Langseth.
Me: How are the bridge watch shifts organized when you’re doing an OBS deployment? Captain: The bridge stands a four-hour watch. The mate on duty stays for four hours, then is relieved by another mate. They work in a four-hours-on, eight-hours-off cycle. Each mate has instructions for how to survey the site with the multibeam before deployment.
Once the scientists decide on the final deployment site, they provide the position, and the mate uses tools on the electronic charts to guide the ship toward that destination. They have to factor in both wind and currents— sometimes the wind has more influence, sometimes the current does—so they adjust their approach accordingly. As they near the site, they communicate constantly with the OBS team on deck, letting them know the distance remaining so the deck crew can prepare. If the deck team isn’t ready, the bridge can slow down or adjust as needed. Sometimes the deck team has equipment issues, so there’s a lot of back-and-forth communication.
Slowing the vessel must be done gradually. As we get closer, the mate calls out the distances: 500 meters, 200 meters, 100 meters. When we’re within 50 meters, the mate gives the “okay to launch.” At that point, we’re still moving slowly toward the site, and the accuracy is good enough—we don’t need to stop exactly on top of the target. Once the instrument is in the water and released, the scientists confirm back with the bridge. The mate on watch records the exact position of deployment in the log. It’s another layer of documentation in case there’s any later confusion about where the instrument was dropped.
Afterward, we hold position while the scientists confirm that the OBS has reached the sea floor. Then they begin their survey pattern. Using acoustic ranging, they determine the instrument’s true resting position. Once the “all clear” comes from the scientists, the bridge proceeds to circle the area in a pattern. When that’s done, they inform the OBS lab and wait for clearance to move to the next site. Once approved, we steam toward the next location.
Me: How many people work on the bridge throughout the day? Captain: There are three mates. David Wolfford is the chief mate; Joselyn White is the second mate; and Matthew Phelps is the third mate. During the day, the mate is usually on the bridge alone. At night, there are two people: a mate and an able-bodied seaman. The seaman keeps lookout, makes rounds, and assists with steering.
Me: How many OBS deployments have you done during your career? Captain: A lot. Ever since we’ve had the Langseth, we’ve been doing OBS deployment projects. Chief Mate David Wolfford worked with me on my previous ship too. On longer cruises, we deploy the OBS units, shoot to them, recover them, and sometimes redeploy them for another cycle. You can have two or three rounds of that—lots of drop-offs and pickups. So yes, there have been many trips. The mates usually enjoy OBS work, it’s hands-on ship handling and a nice change of pace from other routines.
Our next stop is the main lab—the place where every deployment decision begins. Here, the scientists gather around screens filled with multibeam maps, navigation data, and seismic profiles, discussing which part of the seafloor will host the next OBS. First, I met with Cody and Nick.
Cody: I’m the lead technician. On this cruise, when the bridge calls down and says, “Ten minutes to the site,” that’s our cue. We recover Maggie, the magnetometer. Once it’s on deck, we notify the bridge—so they know they can slow down or stop if needed. If Maggie is still out, the ship has to maintain at least five knots; otherwise, it could get pulled under or tangled. Once she’s secured, we move to the A-frame, run the hydraulics, lift the OBS off the deck, and lower it into the water.
Either me or Nick, one of us has to be on deck.
Nick: My job’s a bit of everything. I support the tech group however they need—tools, fixes, anything. The other day the bale lifting points on an OBS didn’t fit, so I used a grinder to shave a bit of titanium so the bale would sit properly. Mostly, we make sure the deck operations run smoothly. The tech team is experienced, so they don’t need much help—but we’re there for safety and support.
Like Cody said, we start by bringing in Maggie, so it doesn’t tangle or sink under the hull if the vessel slows. Once she’s secured, we’re on deck communicating with the bridge, making sure everyone’s in hard hats and life vests. The captain is ultimately responsible for everything, but he trusts us to manage the deck. When we approach the site, we operate the heavy machinery, lift the OBS, and make sure nobody gets hurt in the process.
There are two other marine technicians on board. Gilles and Brian.
Gilles: I make sure every instrument works and that all the data is collected and properly stored. If something stops recording, I have to fix it quickly, so no data is lost. Every dataset, gravity, bathymetry, navigation, depends on the others. If we have great gravity data but no coordinates, it’s useless. So, I treat every data stream as equally important. I also duplicate everything; if one copy fails, there’s always a backup. That’s my main job on this cruise.
(That’s a lot of responsibility.)
Brian: I’m in charge of seismic operations, air guns, winches, that sort of thing. For OBS work, I operate the A- frame. For CTDs, I run the DESH 5 winch (Did I hear that right? I’m not sure). I put everything together and keep it running. During OBS deployment, I’m the winch operator. I have worked with thousands of OBS deployments.
(His answers are short 😊😊.)
Now it’s time to head over to the OBS lab and its extension. What you mostly see here are wires and circuit boards. The extension room, really a converted storage container, is lined with shelves of OBS sensors waiting for their turn at sea. The air smells faintly of salt, metal, and coffee. Tim and Hannah work the midnight-to-noon shift for the OBS deployments.
Tim: Okay. Well, I’m Tim, a senior engineering assistant. My job is to support the electrical side of all the deployments. If anything fails electrically, I’m here to fix it. I also help with the deployment process itself.
(He pauses to think.)
I’ve probably handled… some thousands of OBSs. That includes both recoveries and deployments. On one of the cruises, we deployed eighty instruments and recovered eighty—so, in total, handled about one hundred and sixty instruments within one cruise.
Next, it's Hannah's turn.
Hannah: I’m an OBS technician. Back at WHOI, I’m a senior engineering assistant. I help putting everything together, testing at different stages – from bench testing to full system testing.
A lot of the cruise-planning is also my job. I work on the deck plan, making sure everything fits on board and that the layout makes sense. Dan and I share that responsibility. We also handle shipping and logistics. We have a shipping and receiving office. First, we have to prepare a detailed manifest—basically a complete list of everything we’re bringing. Then we make sure the manifest is accurate and that we have all the gear, sensors, and instrument kits packed correctly.
There’s also hazmat documentation for batteries and chemicals, which has to be declared properly. Once we are at the port, we load everything on to the ship and arrange according to the deck plan we’ve created.
As soon as one cruise ends, we begin demobilization, and that process flows directly into mobilization for the next experiment. This cruise was a bit unusual because it got delayed. We had to make sure the batteries stayed alive during that time, so we opened housings we normally wouldn’t, disconnected and resealed batteries, and then reconnected and retested everything later. It was more repetitive work than usual, but everything worked out in the end, so that’s good.
(She smiles.)
Finally, I talked to Dan and Alan, who work the noon-to-midnight shift for the OBS deployments.
Dan: I’m a senior engineering assistant. I help prepare the instruments and deploy them. Outside of operations on deck, I handle shipping and logistics for transporting the OBS units. This time, we had three trucks, one flatbed from Canoga with an accordion-style tarp system, and two 53-foot box trucks. They had to travel from Massachusetts to San Diego.
We needed all three, partly for space and partly for weight. If we’d packed them into one or two trucks, they would’ve been too heavy to move legally over the road. Since we’re running two OBS deployment cruises back- to-back on this ship, we transported all the instruments for both at once.
Back home, I do design work, improving instruments, maintaining and testing them, and implementing any new design changes. Right now, we’re building forty-two new instruments.
Here comes Alan:
Alan: I’m a research engineer at the Woods Hole Oceanographic Institution, but out here I serve as an OBS tech. My job is getting the instruments ready to go over the side and making sure they’re deployed safely. Back in the lab, I focus on instrument development and maintenance. Out here, I keep an eye out for things that might cause trouble later—issues we can fix or improve.
I've got more questions for him.
Me: How many OBS technicians are on each cruise? Alan: Four. That way we can split into two shifts, two techs per shift. On the next cruise, we’ll have two OBS techs and two OBEM techs from the Scripps Institution of Oceanography. We’ll share the work, one person from each group on each shift.
Me: Do you have to maintain and improve the OBSs often? Alan: Constantly. After every cruise, we go through a full demobilization. We open up all the housings, replace O- rings, dispose of batteries, test every cable and bulkhead. Usually, five to ten percent of the cables get replaced each time. Sometimes we add new components or sensors, but even the basic maintenance takes a lot of time. We could do less, but that would mean more failures, and lower data recovery rates.
Me: Are the OBSs often damaged when you recover them? Alan: Not usually. The cables wear out, and the housings can show corrosion. In rough weather, one might hit the ship during recovery, metal parts can bend, and we might need to weld new pieces. Occasionally, corrosion gets bad enough so that we have to replace sections of the frame before redeployment.
Me: How much time do you usually get between cruises? Alan: It varies a lot. Ideally, about six months. That gives us time to order parts, replace batteries, and do deeper maintenance. But we’ve done it much faster—during the Cascadia experiment, we had only six weeks between cruises to demobilize, overhaul, and ship everything back out. It worked, but it’s not sustainable. Less than six months means we can’t do thorough maintenance; more than six months means instruments sit idle, which isn’t ideal either.
Me: What does it cost to get an instrument ready for redeployment? Alan: The biggest expense is the batteries, around $5,000 per instrument, sometimes more. Other expendable parts add maybe another $1,000. Labor costs depend on what needs repair and welding or fabrication adds up fast.
Me: What other kinds of work do you do besides OBS deployments? Alan: I’ve been in the OBS group since 2007. In recent years I’ve been heavily involved in designing new instruments. The “anglers” we just deployed were first tested a few years ago off the Galápagos, they’ve been very successful. We also have a new fleet of forty instruments nearing completion.
Those two projects took years, starting around the pandemic, focused on replacing obsolete components and improving reliability. Most of my lab time now goes into applying those upgrades, testing new systems, and keeping the infrastructure – the computers, the test rigs, all the diagnostic equipment up to date.
The OBS lab; Every cable replaced, every sensor tested, and every design tweak ensures that when an OBS disappears beneath the waves, it will wake up on the seafloor and send back a piece of the Earth’s story.
By Dilini Walakulu Arachchige
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