On May 6 we posted a description of the various equipment involved in dredging. In this post, we describe the roles of the 8 or so people needed to safely and efficiently dredge the ocean floor.
Let’s start with the people who decide where to dredge: This is done by the scientists, pouring over maps to pick a promising target. Because we are trying to recover fresh volcanic rocks, we scrutinize the maps for features that look … well, volcanic. That is, they appear to be elevated, discrete mounds that are apparently not sediment-covered, both of which we can determine – to a somewhat imperfect extent – by examining the maps we made while surveying before we began our dredging. We also need to consider – based on wind and ocean current conditions – the direction we will move the ship while dredging (for our cruise, we have had to dredge in a generally southeast heading). And, we can only dredge uphill (so the chain basket remains downhill of the crown of the dredge). With all of these considerations – and given that a typical drag over the ocean floor is about 0.5-1 kilometer – the scientists select a starting point near the northwest base of the volcanic feature, and record that point’s latitude, longitude and depth, as well as the course heading and distance the ship should move during dredging.
This information is then conveyed to “the bridge” (the captain and mates), so that they can position the ship. The mate on watch manually drives the ship to the site, and then transitions to the computer-automated Dynamic Positioning System which holds the ship in position. A half hour before arriving at the dredge site, the bridge notifies the engine room.
The crew in the “the engine room” (engineers) have many critical tasks (we will do a post just on them soon) – and one of their tasks is to operate the winch. The winch is the huge machine that runs the trawl wire – either “letting out” wire to allow the dredge to sink to the ocean floor, or “hauling in” wire to pull the dredge up to the surface. When deploying or recovering a dredge, the winch operator (one of the engineers) sits in the winch shack on an upper deck, from which he or she can look down onback deck(called the fantail). It is important that the winch operator can see the deck because hand signals are used when deploying and recovering the dredge.
When the ship is in position and the winch operator is in the winch shack, we are ready to deploy the dredge. On our ship, this operation is supervised by a Resident Technician (ResTech), a person who – among their many skills – is trained to operate the heavy deck equipment needed by the scientists (for safety reasons, the scientists don’t operate the ship’s machinery without supervision). Our two dedicated ResTechs are Josh Manger and Jim Convery. In deploying or recovering the dredge, the ResTech oversees a 4-person team of scientists working on deck: two operate the tag lines, one operates the A-frame, and one (the runner) helps as needed. In addition to supervising the scientists on deck, the ResTech is in communication with the bridge by walkie talkie, and with the winch operator using well-established hand signals. The ResTech is kind of like a maestro– orchestrating the whole operation (see photo of Josh and you’ll see what we mean).