Comments about technological history, system fractures, and human resilience from James R. Chiles, the author of Inviting Disaster: Lessons from the Edge of Technology (HarperBusiness 2001; paperback 2002) and The God Machine: From Boomerangs to Black Hawks, the Story of the Helicopter (Random House, 2007, paperback 2008)

Saturday, January 21, 2012

Concordia Update: More investigative tools

Authorities have recovered the Voyage Data Recorder (see previous post) so the ship's onboard data will be emerging soon.

Meantime, Quality Positioning Services BV has put together a vessel track from the navigational info that Concordia was transmitting in its last hour. Check it out:

The initial allision happens just short of a minute into the video. You might well wonder how it's possible for anyone to put this together when the VDR data and shore radar records haven't been released yet. It's because under ship-safety treaties, ships like the Concordia must carry an Automatic Identification System (AIS) transmitter, which sends a constant update of the ship's position, speed, and course. ("Course" reflects the direction the ship's bow is pointing, regardless of which way the hull is moving.) 

Ships trade the AIS information with each other as a collision-avoidance system, supplementing their radar sets.

AIS information is also captured on shore by the Vessel Tracking Service and AIS base stations. That's the data stream that QPS used in preparing the track video.

Here's a link to a PDF document explaining the company's methodology. QPS notes that the ship first struck the rocks at a speed of 15 knots. Here's one of those boulders, which the ship broke off and carried away, until it returned to shore for the last time:
Self-correction on the ship's propulsion: In this post I wrote that the Costa Concordia might have used thruster pods for propulsion. (Thruster pods, also called azipods, are swiveling units that house electric thrusters, mounted under the hull.)  Rather, Concordia used a variable pitch propeller, powered by marine diesel engines running most of the time on heavy fuel oil (HFO) that's so thick it only flows when heated. Here's my Rena post on HFO and how it differs from diesel fuel. 

Photos of the hull on its side, while confirming that Concordia didn't have azipods, do show that it had a pair of roll stabilizers, which help to prevent parametric rolling from getting out of hand, as on the Pacific Sun. Here's what the Sperry's brand of stabilizer looks like:
 Here's the port stabilizer - it's the red rectangle jutting out:
 Here's a closeup of the stabilizer:
It pivots into the hull to avoid damage during tug movements or docking - that's the purpose of the notch. 

The ship's roll stabilizer is visible from space (photo by DigitalGlobe, from the QuickBird satellite). It's the tiny white object on the ship's port side, about two-thirds the way down the length of the hull, measured from the stern, which is at the top of the image.
I find it interesting that the stabilizer is apparently undamaged, despite the scraping of the hull abaft that position. Such damage to the aft hull on the port side suggests to me that the ship was making a hard turn to starboard at the time it struck the rocks. 

With a stern drive like the Concordia had, a hard turn to starboard (right) shoves the stern to port (the left), which forces the stern against obstacles lying on that side. It might explain why the roll stabilizer appears to be undamaged, even though it juts well away from the hull. Another possibility is that the roll stabilizers were stowed at the time of first impact and popped out later. The VDR data should settle that. In any case it seems likely that the helm was hard over at the time of impact.



3 comments:

  1. Hi, this is one of the best compilation of information on the Costa Concordia sinking. A question, QPS describe their methods in http://news.qps.nl.s3.amazonaws.com/Grounding+Costa+Concordia.pdf but don't describe their source of data. AIS databases only have 2 records (GPS points), one before and one after the apparent collision with the rocks. Plotting those you get a straight line between those points, but we don't know the vessel's path between those points. Did QPS have access to another AIS database, perhaps from digital logs stored on ships close to the Costa Concordia which were receiving more frequent updates than land based AIS receivers?

    Anyways, job well done.

    ReplyDelete
  2. Tony: Good question! I'll post an update if I find out how QPS obtained such detailed track and course data.

    ReplyDelete
  3. Thanks for great sharing. When the required gear is selected, the dog clutch locks that gear onto the output or propeller shaft. stern drive propeller The below propeller brands will fit on your selected MerCruiser engine. However, to ensure proper loading of your engine, please choose the propeller size that most correctly matches your existing propeller. Please use the engine filter above to narrow your MerCruiser propeller options to your specific engine.

    ReplyDelete