Costa Concordia: Investigative tools

Sit-rep on the Costa Concordia: six bodies have been found; sixteen people who were on board have not reported to authorities; the ship may come off the rocks at any time and slide into deep water; and the owners have issued a statement about possible human error that distances them from the captain. An Italian helicopter pulled off an employee yesterday (photo in the Telegraph, from AFP):

Here's the flotilla of used lifeboats, from Wiki Commons:

Because of the rapid heeling of the ship in the final moments, many passengers had to climb down ropes or jump.

In my previous post I mentioned the black box required on newbuild passenger ships like the Costa Concordia after 2002, the voyage data recorder, aka marine event recorder. Here's a photo of such a rig from Transas:

Here's a brochure for one brand, a Raytheon model, of VDR. For a ship of the Costa Concordia's class, a VDR captures the following:

• Position, date, time using GPS.
• Speed log – Speed through water or speed over ground.
• Gyro compass – Heading.
• Radar – As displayed or AIS data if no off-the-shelf converter available for the Radar video.
• Audio from the bridge, including bridge wings.
• VHF radio communications.
• Echo sounder – Depth under keel.
• Hull openings – Status of hull doors as indicated on the bridge.
• Watertight & fire doors status as indicated on the bridge.
• Hull stress – Accelerations and hull stresses.
• Rudder (or Azipod) angle– Order and feedback response.
• Engine/Propeller – Order and feedback response.
• Thrusters – Status, direction, amount of thrust percentage or RPM.
• Anemometer and weather vane – Wind speed and direction
• Main alarms – All alarms mandated by the International Maritime Organization

One channel of main-alarm data that interests me is a time plot of degrees from vertical. When did the ship start to heel over? Late-model cruise ships with a shallow draft and a high stack of hotel-like cabins have a metacentric height that can make them tippy under certain conditions. Here's a Globalspec link to how metacentric height is calculated:

Some conditions that can lead to a capsize are improper loading or a tight turn, particularly if these combine with a stiff wind. Here's a link to the following detailed graphic from the Daily Mail, showing such a U-turn before the ship rolled onto its side:

Note the bow-on profile of the ship on the right of the graphic, comparing how much structure was above the waterline compared to how much below.

While blogging about containerships in distress (such as Rena, another ship that hit the rocks) I promised a post about parametric rolling, in which a ship's physical features interact with heavy seas of a specific wavelength. The result is a harmonic that can dangerously magnify a ship's tendency to roll, particularly when the ship is almost bow-on to the waves. (Traditionally, shipmasters head directly into the waves during a storm, because that was thought to be the safest course.)

While parametric rolling wasn't a factor in the Costa Concordia's loss, I mention it because it's a remarkable phenomenon of the open sea and was unrecognized until the modern era. It's already damaged some containerships, and may have imperiled the cruise ship Pacific Sun during a South Pacific storm in 2008. Dozens of passengers were injured, many by furnishings on the move. Still, Pacific Sun made it back to shore from its "Summer Daydream" cruise, which is pretty amazing since video taken from a helicopter shows rolling so extreme (31 degrees off vertical) that the underside of her hull is visible. Here's an image from the British investigative report, tilted to indicate to readers what the roll felt like from inside: