Action on the Back Deck
8 September, 2010
by Michael Dessner
It really is hard to put too fine a point on waking up to find near perfect conditions during a deep sea voyage. This morning when I rose to find the sun shining through the porthole in my stateroom I leisurely grabbed a shower and cup of coffee and took a stroll on the back deck. Both the girls were already pre-flighted, weights installed, lines packed, almost trembling in the gate to get back into the race. Mark Dennett of the WHOI AUV team had pulled out a couple of his folding camp chairs and was sitting on the stern watching the ocean go past. The skies were light blue with very few high clouds, the sun shining down on an ocean that had settled some overnight, just a lazy 3 foot ocean swell. You just could not ask for a nicer day (knock wood, a comment like that is almost certain to bring a weather change).
Yesterday saw some progress on the processing side of things. Andy had put together a really sweet mosaic that was based on his pulling out snippets of sonar data and then laying onto a canvas in Photoshop. I personally have never been able to make head nor tail of that program, having not attended the 4 semesters of study it seems to require. Fortunately for us, one of the new AUV guys from Woods Hole, young master Kevin, is fairly proficient with the program and he has been able to smooth the transitions between the various layers. It’s smoking hot now. Soon, I hope we’ll be able to share some of this data with the world at large. Mary Ann and Ginger are such capable platforms for underwater work. In essence they have exponentially decreased survey time by two orders of magnitude; but, that amazing stat means nothing if they cannot bring back excellent data. If anyone still has their doubts I assure you when you see the imagery they’re creating on the Titanic you will be convinced: it’s dramatic. One of my personal hopes was to create magazine cover quality sonar imagery of this site, the most recognized shipwreck on earth, and I am comfortable that we have done so already. Tomorrow when the 540 kHz data comes up we will have gone even farther down that road.
Once we arrived on site we dropped a topside transducer to wake our Deep Ocean Transponders and reactivate our Long Baseline navigation grid down on the wreck. These DOTs have been resting comfortably on the ocean floor since we left a week ago; they woke right up and are in place to provide the girls references when they get to the bottom and begin work. All Systems are GO FOR LAUNCH! To the deck and launch stations!
Seldom do you get to work on deck in a nearly flat sea with the sun beating down on you, especially on the Grand Bank! Instead of our foul weather gear we’re reaching for sunblock. We just worked a near flawless launch, having only to slow the ship down just a tad to keep communications with the vehicle as it was streaming behind the ship. But aside from that completely negligible aspect, it was a picture perfect deployment; a good thing since I was running the hydraulics on the LARS. When things go pear shaped, that can be a slightly tense place to stand, a spot where we have seen some strange things in the past.
During our early operations we had a couple incidents of the vehicles activating when they hit the water and swimming to catch back up with the ship instead of streaming behind us. Even though we have long since fixed the software glitch that caused that, you need to be ready for it. Another difficulty we have seen is the line used to deploy the vehicles back-spooling onto the winch on the LARS. While the vehicle is in the water and streaming behind the ship, we let out a couple hundred feet of line before attaching the descent weight and releasing the vehicle to dive to the bottom. That can slack and wrap around the drum; then instead of spooling out, it starts to suck the vehicle back in. A very unpleasant occurrence. If you are running the winch, you have a tendency to be looking at the vehicle and line, you can’t really see the winch drum. If the vehicle suddenly starts coming back at you, that can be a damned confusing moment. Time to break and go get Mary Ann in the water. To the deck!
OK, Mary Ann is also away. We had a little moment back on deck during this launch. Usually just before you boom out the LARS over the stern, pressure must be maintained on the winch line to keep it tight as the LARS goes from horizontal to vertical and the vehicle goes from laying on the cart to hanging in the air. Seldom is that line wound so tight that a ton suddenly depending from it doesn’t pull out a little slack. The result? The vehicle drops from 6 to 18 inches, enough to get your blood moving, trust me. It’s not actually a problem. You just suck it back up tight into the docking head and then finish booming out over the water, winch out, get the vehicle streaming behind the ship for final checks and release.
When I brought in the slack from the descent line today, the chain that is locked to the nose of the vehicle with titanium levers and solenoid releases, popped out! Mary Ann, sensing that her descent weight had been released, started swimming to her first objective so her prop started turning. The only problem was that she was still in the LARS 3,700 meters above the sea floor (or, 4 meters above the water!). It wasn’t a really big deal. We carefully removed the recovery float and the recovery line box, reinserted the decent chain. Tested, reinserted. Tested again. When we were satisfied that it had just not been properly loaded in the first place, we put everything to right and got ready to launch.
However, I had just spent the last half hour living in my head, thinking about what would have happened if we had not caught the problem. In my imagination, I can see the LARS up at a 70 degree angle but still over the deck when the vehicle slid out of the docking head. Most likely it would have bounced overboard with little damage would be done. But in my paranoid state, I got to wondering what would happen if it fell half overboard and then canted with the nose down toward the deck. With the LARS in an upright position, we may have been in a hairy spot at that point. They’re double tough but, bouncing them around on the deck of a ship at sea ain’t my idea of a good time (or a cheap date)!
Anyway, we got everything ready for launch, with me again at the hydraulic control pedestal running the LARS. When I had the vehicle up to about 70 degrees off the deck, it did what it usually does which is drop a bit. Although only about a foot, it seemed like a lot farther and I’d be lying if I said it didn’t scare the crap out of me. But, like I said last week, never let them see you sweat. I eased off the ‘Boom Out’ control so I could have a bit more hydraulic oomph and sucked her back up tight into the docking head with the winch. Everything else was 5 by 5. Ginger is on the bottom doing her thing and in about an hour Mary Ann will join her. We have secured our surface transponder and are turning the boat over the ROV guys. I am going to stay away from the coffee until the jitters leave my system, grab a camera and watch the ROV guys do there thing on this beautiful day at sea.
Until tomorrow, when I’ll be raving about the new high freq sonar, this is Dessner, out.