jspira

I am far (very far) from an expert on such vehicles but I would be quite certain that there are good reasons that the Bluefin 21 cannot go deeper. Perhaps it cannot operate and perform its functions, perhaps it takes on water, perhaps it would sink. I don't know. But I am fairly certain this is not arbitrary.

alex_b

It could certainly go deeper, the question is could it come back up (and in one piece)? The maximum depth is certainly set for a reason and whilst they might be able to recalibrate to reduce the safety margin there may not be that much more they can do.

john398

from the manufacturer
http://www.bluefinrobotics.com/products/bluefin-21/
Depth Rating 14,763 ft (4,500 m)

So after research looks like your right, I was just going on what I heard on CNN which seems they thought could be calibrated to go deeper, oh well

QF WP

Read the full story:
http://www.abc.net.au/news/2014-04-1...mearns/5392440

bimmerdriver

Underwater vehicles such as AUVs are designed for a maximum operating pressure, for which there is an equivalent depth (e.g., 4500 m), which really means msw (metres of sea water). (Sea water is more dense than fresh water, so it weighs more and correspondingly the depth rating in sea water is less than fresh water.)

Just because the depth rating is 4500 m, doesn't mean the unit will implode at 4501 m. Typically, there is a "safety margin" which is typically 25-50%, depending on how conservative the pressure / depth rating is. Diving the Bluefin 21 below 4500 m is not a matter of "recalibration". It's a matter of whether or not the operator is willing to take the risk that the vehicle may not survive going below the recommended maximum depth. If the maximum operating depth exceeded, the failure could be minor (e.g., a sensor such as a camera or sonar could fail) or it could be catastrophic (e.g., the navigation or control system could fail). Modifying a vehicle to dive to a greater depth should be expected to require significant reengineering, such as replacing sensors, strengthening pressure vessels and replacing buoyancy foam for a different material.

Disclaimer: I work for a company that makes underwater vehicles (not for Bluefin). I have no knowledge of their design practices.

polarbreeze

It was set to fly a certain distance above the seabed but, due to imperfect understanding of the underwater terrain when its course was set, that took it too deep so it aborted. They will move it to a slightly different area which is not so deep. A different vehicle will be required to search the deeper parts of the search area.

RadioGirl

Bad idea.

deant

According to some news reports, they have done an analysis of the Bluefin-21 and believe the risk of going deeper is small and acceptable. So they believe that the Bluefin can cover the entire search area.

Himeno

They sort of don't have a choice. Given that Abbot has given them a week to find something or he pulls the plug to "stop and reassess". They don't have the time to get anything better out there.

bimmerdriver

There is always a choice. There are commercially available vehicles that can dive to 6000 m, so it's not like there aren't alternatives. However, if the Bluefin has a 4500 m depth rating, it probably has at least a 10 or 20 percent safety margin, if not more.

Eryeal

Another mystery to add to the mystery:

(CNN) Investigators have determined that the missing jet was equipped with four emergency locator transmitters, or ELTs, which are designed to transmit a plane's location to an emergency satellite when triggered by a crash or by contact with water, the source added.

The ELTs were at the plane's front door, its rear door, in the fuselage and in the cockpit, said the source, who was puzzled over why they appear either not to have activated or, if they did activate, why they were not picked up by the satellite.

Maluku_Flyer

This has been discussed several times upthread. ELTs are designed to function after a survivable crash - not one where the plane is shredded. They are not as robust as the FDRs.

And even after a crash with survivors they don't always work. Oh well, CNN again.

lewko

I think the plan that Ocean Shield is executing is reasonable. They have to locate a piece of debris precisely so they can send the grappler to get it. If they put a lot of sonar devices down there they will be interfering with each other. The alternative seems to be a towed sonar array. They really can't use that simultaneously.

Ocean Shield has a grappler too so it is well equipped to work fast if Bluefin finds something. IMHO there isn't any better than Bluefin.

Abbot is in the middle of all the relatives who want evidence and a scapegoat.

bimmerdriver

The reason the Ocean Shield and the Bluefin are being used is because they are available and they are suitable. The Ocean Shield is of a typical design that's used in the offshore oil and gas industry. Google "offshore support vessel" and you'll find literally hundreds of examples. It was built by DOF, which like many similar companies, operates such vessels. Normally such vessels are equipped with ROVs, or if not, can be easily equipped if required. Based on what I've read about the Ocean Shield, it doesn't have ROVs. The "grapple" will not be used to directly lift debris off the bottom. When (if) they find some debris, they will dive an ROV to take a closer look. If they decide to lift some debris, an ROV will be used to fasten some sort of lifting apparatus to the debris and attach it to the hook on the crane on the surface vessel. There are many vessels similar to the Ocean Shield that already have ROVs. So the Ocean Shield is the right type of vessel, but would need ROVs if it's to be used for recovering debris. Also, there is nothing special about the bluefin. It's a typical AUV outfitted with typical sensors. There are a number of companies that make AUVs which are similar to the Bluefin and which can dive beyond 4500 m without exceeding their depth limit.

Disclaimer: I work for a company that makes equipment and systems used in the offshore oil and gas industry. I've been on a vessel similar to the Ocean Shield.

bimmerdriver

I'm not usually complimentary of CNN, but why bash them for this? If it's been verified that the aircraft had four ELTs, that debunks two things that have been questioned. First, claims that the ELTs weren't detected because there weren't any on the aircraft. Second, claims that the aircraft had a controlled landing. If the aircraft had not just one, but four ELTs, yet none of them were detected, it must have sunk immediately upon crashing, which does not indicate a landing that was either controlled or one that occupants could have survived.

I'm curious about whether the EA 767 had an ELT and if it was detected after it crashed into the ocean.