jimbeetle wrote:
The oil industry has a fleet of ROVs like the 12 that are working on the Gulf spill. They're working at just shy of a mile down now. Is that their limit, or can they work deep enough to be effective at the AF-447 site?
That depends. There are a number of ROVs world wide that are capable of operating at 6000m or 6500m. Only 2% of the ocean is deeper than 6000m, so a design depth of 6000m is often considered "full ocean depth". The deepest point in the ocean is 11000m at the Challenger Deep in the Mariana Trench. There is one (new) ROV/AUV (hybrid, dual mode) capable of reaching 11000m.
But you asked about the ROVs working in the Gulf. I don't know what their range of depth ratings is, though it's likely that others posting here know. It adds some expense to design for a greater depth than needed, so those ROVs might be limited to the depths being explored for oil around the world, or just the depths in the Gulf of Mexico. I would not be surprised if some of them are 6000m rated.
I realize that they're tethered and that would probably add more difficulty. Anything insurmountable?
Difficult: yes. Insurmountable, no. There have been deep ROVs for 20 years or more.
I guess I've been thinking along the lines of a couple of ships controlling a handful of these each for a very deliberate visual search that, if nothing else might rule out areas.
The search rate for ROVs is very low compared to other tools available. At this point the AF447 search needs to cover a wide area. The best visual range I have seen in the deep ocean is 20m, and 10-15m is more common. That limits a visual swath to about 30m, and at 1knot max transit speed, that covers about 1sq-km/day. The BEA site lists 5sq-km/day search rate for the ROVs they had, but that is likely using the ROV's sonar, not its cameras.
Also, ship time is one of the largest cost factors, so minimizing the number of ships is important. I'm not sure what the state of the art is for number of ROVs from one ship; I'm sure it depends on operating depth and other conditions. I have never seen more than one per ship, because of the difficulty of entanglement, but I expect that they are doing more than that at the oil spill site. Some differences there: the depth is "only" 1500m, and the ships are standing still or moving very slowly.