Francis Keys bridge hit by ship. Bridge collapses, mass casualty event.

[tahuyaman]

You need water flow over the rudder. The speed over ground of eight knots would provide at least some steering. Yes the propwash would provide more, but if the engine was in reverse, there would be no propwash and the rudder would operate in reverse form the way it would with normal waterflow. Plus, if the ship is single screw, the stern will tend to move in the direction that the prop is rotating. I had a twenty-seven-foot sailboat and no matter what you did with the rudder when in reverse, the stern moved in the direction the prop turned. To maneuver backwards, I had to build up some speed, then shift into neutral, and then turn the boat.

No prop wash means no steering by the rudders.

 

[tahuyaman]

IF the ship was having electrical problems before leaving the dock, the insurance company won't be able to call it an act of God. It was a maintenance failure. What's going to be interesting is what orders the captain got from the owners. If they ordered the ship to sail despite knowing it had electrical problems they are going to be in big trouble. They might even be facing murder charges for reckless endangerment.

Where are you getting this “act of god stuff?” Mechanical failures are not an act of god.

This ship was recently inspected and judged to be seaworthy and authorized to have access to US ports.

 

[AZrailwhale]

No prop wash means no steering by the rudders.

Wrong, I've got eighteen years of sailing experience. The only thing that matters is water flow over the rudder. That can come from propwash or movement through the water. Sailboats can steer quite well and many don't have engines at all. Plus many large ships have twin screws and a single rudder so the propwash doesn't meet the rudder at all.

 

[AZrailwhale]

Where are you getting this “act of god stuff?” Mechanical failures are not an act of god.

This ship was recently inspected and judged to be seaworthy and authorized to have access to US ports.

Another poster was calling it an act of god. I was pointing out that a mechanical failure wasn't an act of god.

 

[CarlinAnnArbor]

 

[RoshawnMarkwees]

Then you have no clue how powerful currents can be. Plus the ship is so big, the it’s almost a sail if the wind is strong and helping the currents.

Every ship captain or harbor pilot would agree with me 100%.

My research is suggesting higher tides nullify current drift and shallow water produces squatting which slows large vessels. Both scenarios would deter loss of lateral control. I can’t find any tide charts other than forecasts.

 

[skye]

Very interesting thank you!

 

[CarlinAnnArbor]

Very interesting thank you!

Definitely makes you wonder. I really don't trust this current government

 

[tahuyaman]

My research is suggesting higher tides nullify current drift and shallow water produces squatting which slows large vessels. Both scenarios would deter loss of lateral control. I can’t find any tide charts other than forecasts.

High tide exchanges, the difference between low and high tides, typically are high current areas. Typically tide charts are extremely accurate. Tide charts also tell you about currents as they too are predictable.

 

[RoshawnMarkwees]

High tide exchanges, the difference between low and high tides, typically are high current areas. Typically tide charts are extremely accurate. Tide charts also tell you about currents as they too are predictable.

You need to find the charts for the time of the incident. I can’t find them. Everything is forecast only.
Still, the two dynamics of low tide and high tide would theoretically counter current drifting in a harbor. A river or open ocean would yield different effects.

 

[tahuyaman]

Another poster was calling it an act of god. I was pointing out that a mechanical failure wasn't an act of god.

Ok.


Calling a mechanical failure resulting in a catastrophic event is not very smart.

 

[tahuyaman]

You need to find the charts for the time of the incident. I can’t find them. Everything is forecast only.
Still, the two dynamics of low tide and high tide would theoretically counter current drifting in a harbor. A river or open ocean would yield different effects.

Tides are predictable. It’s not like predicting the weather. They don’t happen randomly. You can accurately list the high and low tides years in advance.

 

[para bellum]

Then you have no clue how powerful currents can be. Plus the ship is so big, the it’s almost a sail if the wind is strong and helping the currents.

Every ship captain or harbor pilot would agree with me 100%.

There was no wind, and the current was not more than a half-knot. It was a 1.2 foot tide and the collision with the bridge was 50 minutes before low slack.

There are no real narrows in that channel- it's a small harbor and there is free flow in and out. So the current was not really a factor, other than it was going the same direction as the ship so it wasn't helping...

That harbor is so small and the current is so light that time of departure is probably not even timed to the tide. Whenever the current is a factor, you always always time your departure for slack water at the point of the strongest current. i.e. any narrows or shallows between the port and destination or open water.

 

[RoshawnMarkwees]

Tides are predictable. It’s not like predicting the weather. They don’t happen randomly. You can accurately list the high and low tides years in advance.

I’m aware. But I can’t find those stats for the time of the incident. Only forecasts.

 

[RoshawnMarkwees]

There was no wind, and the current was not more than a half-knot. It was a 1.2 foot tide and the collision with the bridge was 50 minutes before low slack.

There are no real narrows in that channel- it's a small harbor and there is free flow in and out. So the current was not really a factor, other than it was going the same direction as the ship so it wasn't helping...

That harbor is so small and the current is so light that time of departure is probably not even timed to the tide. Whenever the current is a factor, you always always time your departure for slack water at the point of the strongest current. i.e. any narrows or shallows between the port and destination or open water.

So, you’re suggesting that the ship’s change in direction was almost exclusively a result of steering, not natural water flow?

 

[skews13]

You have great detail which I think prevails but I do read other details that do not confirm that the engines never started up again?

The Ship​

Facts and figures for the MV Dali

1. Named after Salvador Dali
2. Built in South Korea from October 2014 to March 2015
3. Displacement of 149,000 tons
4. 984 feet length by 158 feet wide
5. 49 foot draft (hull depth in the water fully loaded)
6. Propulsion is a single shaft with a fixed pitch propeller
7. Power is from a MAN-B&W 9S90ME-C9.2 two stroke diesel engine of 55,000 hp
8. Design speed is 22 knots or 25 mph at 82 RPM
9. Fuel usage is around 200 tons per day
10. Engine cylinder bore is 900 mm and stroke is 3260 mm (I think 9 cylinders)

I was not able to find a trustworthy number for fuel consumption but 200 tons of heavy fuel oil per day is close. At that rate of fuel burn it is obvious why optimizing the engine and propeller is an important design task.

The Engine Room​

The cargo type ships (bulk, oil, container, LNG, etc) usually have just one propeller and one engine. In this ship the engine turns at just 82 RPM, matching the optimal rotational speed of the propeller, so no reduction gear is needed. There is also no reversing gear so, to generate reverse thrust, the engine is stopped and restarted turning the opposite direction.

In a big ship it is most accurate to think of all the equipment in the engine room as the engine. The ship’s main engine can not operate without all of the other equipment around it. The main engine does only one thing — it turns the propeller. This is very different from a car engine where the engine provides all the power to operate the vehicle. In addition to the main engine is three or more auxiliary engines and all they do is generate electricity. That electricity is used to power everything on the ship (except turning the prop). Everything includes systems needed to operate the main engine itself.

This is a cutaway of a cargo ship (not exactly like the MV Dali but close enough). You can see the main engine attached to the propeller shaft and behind it are three purple things which are the auxiliary engines. Ships can certainly have more than three aux engines depending on how much power is needed and the MV Dali has four.

The Operation and Power Loss​

Everything is run from the aux engines including the fuel feed pumps, lubricating oil pumps, cooling water pumps, and the exhaust valves (hydraulic actuators controlled by computer). Without the aux engine electric power that huge beast of a main engine is dead weight. The other systems run by the aux power are the rudder hydraulic pumps (two units), lights, navigation, communication, and almost everything else on the ship.

During port maneuvering at least three aux engines are operating and synched to the power bus so even if two engines go down the third engine can still run the ship. It looks to me like all the power was lost over the entire ship which means that all the aux engines shut down or the entire aux power bus tripped of line. After that the main engine would have shut down and the rudder locked in place. At that point the Francis Scott Key bridge was doomed. There was not enough time to restart the aux systems and restart the main engine before hitting the bridge pier - although the crew really tried.

The rudder locked at whatever position it was when power was lost since both hydraulic pumps (for redundancy) need electric power from the aux engines. The ship was coasting but something started the bow turning right. Maybe it was a cross current or maybe the helm had turned the wheel slightly to the right for a small course correction. It takes a few seconds for the 100,000 ton ship to actually start turning but eventually it did and headed directly into the bridge pier.

The Worst Possible Timing​

It’s hard to say how bad the timing was for losing all power. If the incident had happened a minute earlier the engine room crew could have recovered power (at least to the rudder) and avoided the impact. If the power loss had happened maybe 15 seconds later the ship would have coasted under and through the bridge without striking anything (maybe a very close call though). But that is not what happened and now we clean up the horrible mess.

 

[para bellum]

So, you’re suggesting that the ship’s change in direction was almost exclusively a result of steering, not natural water flow?

The rudder is constantly being adjusted when a vessel is underway. Based on the ships track and the video, I would say the rudder was slightly to starboard when the power was lost. The rudder needs hydraulics, it would have stayed in whatever position it was in when the power was cut.

 

[tahuyaman]

I’m aware. But I can’t find those stats for the time of the incident. Only forecasts.

What do you mean by forecasts? Tide charts are completely accurate. There’s no problem in determining when high or low tide was three days ago.

 

[tahuyaman]

There was no wind, and the current was not more than a half-knot. It was a 1.2 foot tide and the collision with the bridge was 50 minutes before low slack.

There are no real narrows in that channel- it's a small harbor and there is free flow in and out. So the current was not really a factor, other than it was going the same direction as the ship so it wasn't helping...

That harbor is so small and the current is so light that time of departure is probably not even timed to the tide. Whenever the current is a factor, you always always time your departure for slack water at the point of the strongest current. i.e. any narrows or shallows between the port and destination or open water.

I think you’re wrong on that.

 

[RoshawnMarkwees]

The rudder is constantly being adjusted when a vessel is underway. Based on the ships track and the video, I would say the rudder was slightly to starboard when the power was lost. The rudder needs hydraulics, it would have stayed in whatever position it was in when the power was cut.

But didn’t the boat change direction after power was lost?