By Dave Lovalvo, Dive Supervisor
April 12, 2012
It’s 6 a.m. and the lights have come on. Our two underwater vehicles, Little Herc and Seirios are being prepared for their “electronic wakeup.” The engineers move through their pre-dive checks, each with a specific task to carry out. Meanwhile, other parts of the ship are beginning to make a transition.
Up on the “01” deck, in the back row of our command and control room, the mapping team is finishing their evening shift, while the pilots, co-pilots, navigators, and video engineers move quietly to their front-row stations. Pre-dive checklists are read and responded to by engineers on deck and in the command and control room. Compensating fluids will be topped off, camera domes will be cleaned, and all equipment mounted on the vehicles will be visually checked. Both vehicles will be brought up on our low-voltage system, to ensure all critical equipment is working properly.
Weather, sea state, and the status and safety of all onboard operations are discussed and considered. Concurrently, a public announcement alerts everyone, that high voltage operations will commence on the aft deck (the aft deck is at the very back of the ship and is where the vehicles are launched from). This is the final check of the underwater vehicles prior to proceeding with their launch.
From pre-dive protocol to the launch of remotely operated vehicles, Okeanos Explorer crew members carefully follow detailed procedures. Click on the image to view a video that illustrates dive preparation timeline, as described Dive Supervisor Dave Lovalvo. Video courtesy of the NOAA Office of Ocean Exploration and Research, Gulf of Mexico Expedition 2012. Download (mp4, 50.5 MB).
It’s 7:55 a.m. While final checks are made in the command and control room, the deck group has begun to prepare the aft deck for launch. The securing straps are removed from the overboard sheave, which is mounted on the upper part of the aft deck A-frame (the A-Frame is a hydraulically driven structure mounted to the deck that we use to launch Seirios). The sheave is used to guide the main power cable that feeds Seirios and Little Herc.
The lines on the “air tuggers,” which aid in controlling the 3,000-pound dead weight of Seirios during launch, are checked and fastened to the vehicle’s frame. As the deck hydraulic systems come alive, the lift crane used for launching Little Herc is moved into position and prepared for attachment to the vehicle. The deck is now well on its way to be prepared for launch.
Below decks, the massive traction winch stores the 8,200-meter underwater cable, which attaches to Seirios while it also moves the cable in and out during the dive. With all checks completed, the operator at the local control in the winch room will fire up the 100-horsepower hydraulic drive motor. All major systems required for launch are now awake and ready.
The dive supervisor arrives on the aft deck to make certain that all personnel work together, clearly communicate, and adhere to all safety aspects of the launch. They will verify effective communication with all personnel involved in the launch.
The “Deck,” or what we call the “Bosun,” the “Winch Operator,” who is located down in the winch room; the “Bridge,” who is the person responsible for controlling the ship; the “Pilot,” who is in command of the underwater vehicles; and the “Navigator,” who attends to the navigation of ship and underwater vehicles are all contacted for a radio check.
Ship control, winch control, and A-frame control is now passed from their “local” position to an aft control station located on the “02” deck. This gives the major operators of this equipment a birds-eye view of the aft deck and launch area.
The only major piece of equipment used in the launch that is not controlled from this location is the lift crane for Little Herc. This is done from the aft deck, where the visibility for that operation is best.
Video footage captured by the Little Hercules remotely operated vehicle (ROV) and Seirios camera platform during the April 12 ROV dive from NOAA Ship Okeanos Explorer during the Gulf of Mexico 2012 Expedition. The dive was conducted at site "BiloxiB" on the Biloxi salt dome and focused on ground-truthing water column anomalies imaged by the Okeanos Explorer's multibeam sonar that are believed to be active seeps, or areas where gas naturally escapes from the seafloor. A variety of interesting seafloor habitats were imaged during the dive. Video courtesy of the NOAA Office of Ocean Exploration and Research, Gulf of Mexico Expedition 2012. Download (mp4, 311.0 MB).
The launching of Little Herc and Seirios can be a bit tricky. It’s what we call a two-body system -- they go down together. The two vehicles are connected to each other by a “soft” electro-optical tether. The tether is 30 meters in length. Seirios is also attached to the ship, which is done using the 8,200-meter armored cable that is stored on the large traction winch below decks.
For launching, Little Herc is moved out on the aft deck from its hangar on a hydraulically driven trolley. Once out on deck, it is positioned directly underneath the lift crane. A special quick-release mechanism is used to attach Little Herc to the lift line. Once that is completed, Little Herc is lifted into place and positioned hard against the underside of the tripod-looking device with a tire on the bottom. This device is called a “swing arrester” and it is there to do just that: arrest the swing during launch. If that were not in place, and Little Herc was just suspended from a line, the movement of the ship would make controlling the swing of Little Herc impossible.
Little Herc is put in the water first. The vehicle is picked up and swung over the port side of the ship and is held just over the water until power to both vehicles is turned on. When power and communications is established on both vehicles, Little Herc is put into the water and a line is pulled, actuating the quick release lift mechanism. At that time, the vehicle is now free from the lift crane and it is driven behind the ship to a distance equal to the length of the soft tether (30 meters).
Seirios is launched next, using the A-frame mounted on the centerline of the aft deck. The winch and the A-frame, which as mentioned earlier, are both controlled by an operator on the “02” deck, pick up Seirios and slowly move it aft. The tugger lines that were attached to Seirios earlier are used to help control the vehicle as it is slid back toward the stern.
While still on the deck, the final movement that lifts the vehicle into the water is carefully timed according to wave heights. Once Seirios is in the water, all tugger lines are removed and the vehicle begins its descent. Seirios is lowered by the winch operator on the “02” deck at 15 meters per minute. Little Herc is driven down at a similar rate, always staying equal to or slightly deeper than Seirios.
Once the vehicles reach 50 meters, a series of final checks are completed. If all systems are good, the winch control is taken over by the co-pilot in the command and control room and the vehicles continue the dive.
