Tuesday, 17 July 2012
Good morning and happy halfway day science fans! Cigars and brandy as is a sailor’s tradition? Not likely, but a new day brings new opportunity for OBS excellence. I think everybody is settling into their roles and their schedules at this halfway mark of the cruise. There seems to be a good rhythm about the ship and morale is still as high as it was when we set sail a week ago. On the agenda for today is a set of deep water recoveries and finally some shallow water ops with Jason making a reappearance after a brief hiatus. John and I had the fortune of being first up, as usual, on the 0000-0400 watch. We were scheduled for a deep water pickup shortly after we relieved. To give you a better idea of what that entails, I can break it down a little bit. While procedures can be monotonous and mundane, it is often that they are written in posterity from mistakes and lessons learned. For novices like us who are just getting our feet wet with Ocean Bottom Seismology, it proved quite helpful to read it in its entirety. Sparing you all the details, here is a brief summary of how recovery happens if there aren’t any snags:
First, we need to get on site and in range of the instrument. Once we have closed within 1NM (Nautical Mile) of the instrument, proper acoustic communication with the transponders can begin. There are two transponders, an internal and an external, that need to be communicated with individually. The internal is enabled and burned first, which releases the OBS from the seafloor. A second command needs to be sent to the internal followed by an optional command to the external transponder to accelerate the release/burning process. At that point we can calculate the rate of ascent, and its approximate arrival time at the surface. The bridge, having a bird’s eye view of the surrounding ocean, usually puts the first visual fix on the floating OBS. At that point, we can snag it with a long hook and pull it onboard. Voila! Mission complete.
So, with that bit of knowledge on what the day will consist of, John and I relieved in the dead of night and were ready for action! There are certain advantages to doing it in the night, the main one being that there is a strobe that is activated on the OBS making it significantly easier to locate, and the overall operation go much smoother. It turned out that we got an added bonus with our retrieval as well. The lights on the ship had attracted a small group of fish, which in turn attracted a pod of dolphins. Watching them go crazy in the spotlight was definite added excitement to our retrieval. Our deep water ops went very smoothly throughout the day, but things wouldn’t continue on that way….
After we finished our deep water ops, we headed to a shallower location in about 175 meters of water. Acoustic communications were smooth, burn and release sequence went as planned, but when the winch was reeling the OBS in… SNAP! The line broke and the TRM went plummeting back to the seafloor. We could still talk to the instrument, so we knew it generally where it was and that (like it had done several times before) it was upside down. Not to fear, we had Jason, and the team was only a few hours away from a planned deployment anyway. It was time to get him in the water and initiate the rescue sequence! As I write, Jason is in, TRM has been located, now we just have to bring it up. Stay tuned to tomorrow’s blog to see how this saga ends and another begins…. Time to relieve the watch, check back with y’all tomorrow!