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ContinuousWave: Small Boat Electrical
AIS Data for COSTA CONCORDIA
|Author||Topic: AIS Data for COSTA CONCORDIA|
posted 01-19-2012 03:01 PM ET (US)
The website linked below contains the best data I have seen regarding the AIS track of the cruise ship COSTA CONCORDIA prior to her capsize.
From that website you can download a PDF document that has exemplary details:
posted 01-19-2012 04:01 PM ET (US)
Click on the chart and then go to full screen.
posted 01-19-2012 05:35 PM ET (US)
So sad - and a pitiful display of shipdriving.
posted 01-19-2012 06:54 PM ET (US)
"So sad - and a pitiful display of shipdriving."
Is your comment before or after impact?
I will agree on the before but quite possibly very good after. This track could represent the quality of decision making post-fact as it could be argued that there needed to be time to evaluate the damage before bailing out to the nearest port.
I think we could discuss the decision of putting it on the rocks or keeping it out in more open waters, possibly facilitating a quicker evacuation.
Caveat being, did the Captain make any good decisions period. Or did one his officers take over?
posted 01-19-2012 07:23 PM ET (US)
Regarding the animation and the software used: does anyone know how the software determines the attitude of the vessel? At times, the outline of the ship appeared to be moving sideways, which was probably accurate, but how can you determine that with just HDG and COG numbers?
posted 01-19-2012 07:25 PM ET (US)
Never mind. Apparently, I answered my own question. I was mistaken in thinking these two numbers would be the same all the time.
posted 01-19-2012 08:10 PM ET (US)
David--Thanks for the pointer to the animated AIS information play back. It shows that the COSTA CONCORDIA was rather skillfully driven onto that shoal, or else very good luck was provided.
Dave P--the AIS data for COG and Heading are often different. I have noticed this from watching ship tracks in the Detroit River where there is a significant current running. The ship heading is not always the same as the actual course made good.
posted 01-19-2012 08:13 PM ET (US)
Most of these commercial vessels have a heading sensor. The GPS computes the COG.
posted 01-19-2012 08:24 PM ET (US)
That's what confused me. I do not have a heading sensor, so on my boat, the heading is only accurate if I'm moving and it almost always the same as my COG.
It stands to reason that a $600M cruise ship would have a heading sensor, and not a seven year-old Raymarine chartplotter...
posted 01-19-2012 09:26 PM ET (US)
Scooter - Pitiful display of driving for the beach and sideswiping a known hazard. He lost situational awareness and the handling characteristics of his ship - advance and transfer.
Once he realized he was in trouble, bringing her around and putting her aground very good.
posted 01-19-2012 09:59 PM ET (US)
I disagree with the assessment of the captain purposely and skillfully grounding the ship. To me, it looks like a broadside downwind drift, about 50 minutes at less than 1 knot, that brought her ashore. I think they were just insanely lucky.
posted 01-19-2012 10:19 PM ET (US)
If the ship was driven or drifted, probably depended on If the engine room was breached during the allision.
Or if her propulsion was still functioning.
When you think of how fast she sank, it's good that their
final position was shallow.
AIS tracking does not always give a good course/position
marker. It is used more for relaying vessel information
to other vessels for communication with VHF, and as a back up check for course & position, as it does not adjust for set & drift.
For shipboard navigation, radar is usually the primary course/position indicator.
posted 01-19-2012 10:40 PM ET (US)
AIS give the vessel position per GPS and its heading per the heading sensor, usually a magnetic compass. What could be more accurate?
The recorded AIS track shown in the animation shows the stern moving out after hitting the rock. It looks precisely accurate, to me.
posted 01-19-2012 10:41 PM ET (US)
This thread is about the AIS data. Debates about the seamanship can go in the general discussion.
posted 01-20-2012 06:39 AM ET (US)
John Konrad from gcaptain narrates the event...
posted 01-20-2012 07:55 AM ET (US)
"It shows that the COSTA CONCORDIA was rather skillfully driven onto that shoal, or else very good luck was provided."
I agree. The AIS data replay makes it look like they used side thrusters to urge the ship to rest parallel to the coast. Based on the size of the gash in the hull, water had to be coming into the hull at a tremendous rate so manueverability would become compromised quite quickly as it took on water.
posted 01-20-2012 08:06 AM ET (US)
The ship would have been providing True heading from the ship's gyrocompass.
If she had lost main propulsive power, not backup household lighting, she wouldn't have had thruster capability.
posted 01-20-2012 01:41 PM ET (US)
After listening to John Konrad from gcaptain, I am leaning toward lucky myself.. Putting the ship on that beach was luck. The only thing I see as skillful is the decision to use the bow thrusters as quickly as they did to slow the momentum of the ship down.
posted 01-20-2012 02:31 PM ET (US)
Without the wind and or current pushing the ship towards shore the bow thruster would probably not have done anything but spin the ship around in circles. If the wind and or current was going the other way they probably would have sunk in deep water. I think they basicly drifted the mile to shore in about an hour as best I can tell. Very lucky indeed. It could have been much worse. And another thing, the ship is 17 levels which makes it so top heavy heavy and affected by the wind. It would blow over well before it got to the point of sinking. The way a ship like that would lean would mean they could only use lifeboats on one side. They should have twice the lifeboat capacity for that reason alone.
posted 01-20-2012 04:58 PM ET (US)
Fascinating narrative and animation.
posted 01-20-2012 08:44 PM ET (US)
News tonight mentioned in passing that they dropped an anchor to swing the ship to help with the grounding. I have not seen anything to confirm this.
posted 01-21-2012 09:29 AM ET (US)
If anyone has found a link to the actual AIS data, please share it.
I can't tell if Konrad has the data or if he is just operating the play controls on the animation provided by the QPS Marine Software website. [Later in the video it becomes obvious that Konrad is just operating the controls of the same AIS animation that everyone else can also see. He does not have the software or the data.] Konrad mentions that the data came from a AIS shore station on the island of Giglio, but I have not seen anything that supports that published elsewhere.
Re the narration track, one bit of advice is to not record a narration track when there is a loud background noise--some sort of repetitive pumping noise--in the background.
Konrad refers to the vector line projecting forward from the ship as "its momentum," but I believe that this is just simply an extension of the ship's current COG and extends in proportion to the ship's speed. There is no calculation involved in this vector that employs the weight of the ship or the resistance to travel through the water, unless a fantastic amount of data crunching is being done by that QPS Marine Software being used to display.
Konrad also says the vector originates at the ship's "center of rotation" but I believe that is wrong. The vector originates at the location of the sensor. Unless there is a fantastic amount of mathematics being applied, I don't think the AIS system calculates the center of lateral resistance or other dynamic force focus on a ship. It just knows where the position sensor is located relative to the bow and stern and each side of the ship. This is programmed into the AIS transponder when it is set-up. The current COG is project from there.
If other readers are familiar with QPS Marine Software perhaps they could comment about its display, particularly in regard to the forward projecting vector having any notion of momentum in its calculation and the origin of the vector having any notion of being from the center of lateral resistance of the hull.
Thanks to jimp for introducing the proper terminology, "advance" and "transfer" in regard to ship movement when turning. "Advance" is the distance covered in the time between the rudder being put over and the time it takes for the ship to achieve a steady new course. The horizontal displacement of the ship in this period is referred to as the "transfer."
posted 01-21-2012 09:57 AM ET (US)
Re the projecting vector shown on a ECDIS (electronic chart display and information system) or other display showing AIS data and whether or not it represents momentum:
Momentum is defined as just
p = mv
m = mass
Since the AIS display tends to draw the forward projecting vector in proportion to ship speed, it does have a sense of being proportional to momentum. However, I do not think that the AIS display adjusts the length of the vector based on the ship's mass. The AIS display shows a projecting vector that gives a sense of where the ship's position will be at some time in the future. Ships moving at high speed get a longer projecting line than ship's moving at low speed, even thought the mass of the ships may be quite different. AIS wants to show the relative future position of ships at their current speed. Thus I do not find that the projecting vector shows momentum.
posted 01-22-2012 10:49 AM ET (US)
Having given some further thought to this, I am now convinced that the typical AIS display of a target which provides a forward projecting vector does not include any notion of momentum in that vector. The AIS system is a collision avoidance system. The AIS display projects the path of a target vessel based on its current speed and heading in order to give the observer a sense of where that vessel will be in the future if the vessel maintains its current course and speed. The observer does not particularly care about the momentum of the target vessel. The observer just wants to see the projection of the vessel's current course and speed into the future so the observer can look ahead in time. In terms of avoiding collision, it would be confusing if the projecting forward vector was adjusted for momentum. A large ship moving at a moderate speed would have a much longer vector than a smaller ship moving at the same speed, and this would tend to cause confusion in terms of collision avoidance, as far as I can see.
I don't know if there is a standard or recommended practice for projecting the target course and speed. If anyone knows of a reference that promulgates such a standard I would be interested to learn about it. It is my experience that systems like AIS have been developed by participation and collaboration of a many smart people, and it would be interesting to know what has been recommended for displays to show.
posted 01-22-2012 10:59 AM ET (US)
[Moved to SMALL BOAT ELECTRICAL to help focus the discussion on the AIS information and less about general comments on the sinking.]
posted 01-22-2012 11:01 AM ET (US)
David--Thanks for the comment that the ship heading would be derived from a gyro-compass. It did not occur to me that a large ship would most likely have a gyro-compass as opposed to a magnetic compass.
posted 01-22-2012 12:10 PM ET (US)
Regarding the display of a vector from an AIS target that shows a projection of the current course and speed, this may be referred to as course trajectory. I found that at least one AIS software package computes the course trajectory by including a factor for rate-of-turn, if this data is available. The course trajectory will be displayed as a curved line if rate-of-turn data was sent by the AIS target, for example:
Note that the projection of course trajectory occurs from the sensor position, as I mentioned earlier. Cf.:
posted 01-28-2012 10:18 AM ET (US)
Most AIS displays include calculation of closest point of approach or CPA. It seems quite reasonable that AIS software would be projecting the future position of target vessels relative to the AIS receiver vessel so that the CPA could be calculated. For each target vessel, the AIS software has to project its position into the future, and at the same time project the AIS receiver vessel's position into the future. Then the software must calculate the range and bearing to the target, and find the CPA. In the process of doing all of that, the software has already projected the future position of all the target vessels, so it is not particularly difficult to just add those vectors to the display of the target ships.
In the case of PolarView NS, the course trajectory is shown for a projection into the future of five minutes.
posted 01-29-2012 10:27 AM ET (US)
Re the use of a gyrocompass versus a magnetic compass on a large ship, I received an email from a reader--a ship captain--who informs that a magnetic compass is required equipment.
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