Baltimore's Francis Scott Key Bridge Collapses after Ship Strike

[Vanadium 50]

I'm not sure what good having a backed up navigation does if you don't have the ability to steer. ("Where am I?" "You're in a boat!") Radio, however, is battery-powered. I believe that's an actual requirement, not just a good idea.

 

[Baluncore]

Ships rudders are usually controlled by hydraulics. The hydraulic pumps are usually electrically powered. Short rudder deflections will be used to maintain, or to change course. The problem with loss of rudder control is that you do not know you have lost it until you need it.

The hydraulic actuators employed for rudder control are fitted with pilot operated check valves. Fluid pressure, applied to one side of the actuator, also opens the return check valve on the other side. When hydraulic pressure is not being applied to move the rudder, those valves hydraulically lock the rudder in position against the sea.

If electrical power is lost, or a one-sided hydraulic failure occurs, then the rudder may well be left, locked in an offset position, until an engineer can reach the rudder-control machinery space, and take over manual control.

A one-sided hydraulic failure may initially make turning one way possible, but returning to straight ahead may then be found to be impossible.

Loss of rudder control most easily explains the curved collision course.

 

[Swamp Thing]

 

[sophiecentaur]

There is a lot of ship underwater to resist such a motion and it would take a substantial wind to move the ship a significant amount in 4 min. Also typically a night the wind is usually light, especially in a harbor.

The ebbing tidal water from that channel to the west would have far more effect than the light breeze and, in the video, it says that the direction would tie in with the ship turning. (Although it was not far from slack water at the time.)

 

[gleem]

When hydraulic pressure is not being applied to move the rudder, those valves hydraulically lock the rudder in position against the sea.

The ship was on a constant heading down the channel (or should have) when the power went out. If the rudder was locked then it should have continued undeviated down the channel. It did not.

It was less than one hour before slack water on that date. The high water mark was only 1.09 feet and only inches from the low water mark, so the current is negligible.

I'm not sure what good having a backed up navigation does if you don't have the ability to steer.

The equipment records the track of the ship so it might provide some useful information. I also would assume they would have lost their AIS and with no lights they would be a hazard to shipping.

 

[Baluncore]

The ship was on a constant heading down the channel (or should have) when the power went out. If the rudder was locked then it should have continued undeviated down the channel. It did not.

How do you suggest the vessel maintained its position, within the narrow dredged channel, without using the rudder?

 

[Flyboy]

Regarding the heading change after loss of power, I saw a video suggesting that the change was a result of changing channel geometry from a side branch of the waterway, which in turn applied forces on the ship.

Lemme find the video.

Edit: found it.

 

[sophiecentaur]

How do you suggest the vessel maintained its position

You mean 'heading' not position? Hat could cause a change if the rudder is fixed amidships?

The wind couldn't have been relevant but water currents (tidal and river flow) talk a lot more on a large hull.
I was looking for information about tidal streams in the location but couldn't find any small scale details. But i do know (from information about the Solent) that the tidal streams are often not in step with the tidal levels (I mean the rate of change of). That stream from the west could have nudged the stern of the ship to the east, which woud be equivalent of the rudder turning the ship to the right.
The narrow, deep channel would also have an effect, which the pilots would know all about (more than our speculations)

 

[Baluncore]

You mean 'heading' not position?

NO. I mean position relative to the centre line and banks of the narrow channel.

Channel bank suction effects and prop walk, both at low tide, would require continuous small rudder corrections to move back to the middle of the channel. The heading is quite irrelevant, in that avoiding being sucked onto a bank is more critical than pointing the right way.

The vessel would be making small rudder changes sufficient to correct deviations within the dredged channel. Those changes would necessarily result in the average compass heading being correct.

If excessive rudder changes were made, bigger changes would be required to remove the accumulated angular momentum, and the track could become unstable at that vessel speed.

 

[sophiecentaur]

NO. I mean position relative to the centre line and banks of the narrow channel.

Lateral position: yes, spot on.

 

[gleem]

How do you suggest the vessel maintained its position, within the narrow dredged channel, without using the rudder?

Channel bank suction effects and prop walk, both at low tide, would require continuous small rudder corrections to move back to the middle of the channel. The heading is quite irrelevant, in that avoiding being sucked onto a bank is more critical than pointing the right way.

Unless something is changing rudder corrections are not needed when running down a straight fairway. Regarding the bank effect We do not know how big it was if it was a factor.

I estimated that the ship if in mid-channel was 30 yds from the marked channel edge and an additional 45 yds from the 30 ft depth contour during much of the channel until it hits the entrance to the Curtis Bay channel to starboard which is 880 yds wide with the distal side of the channel being about 500 yds from the bridge.

The ship traveling 9 mph takes about 1.24 min per boat length. It took 4 minutes from engine failure to collision with the bridge which puts it at 3.22 Boat lengths (0.6 m) from the bridge when power was first lost. That puts it in the Curtis Bay channel entrance where the bank effect goes away until it reaches the distal end of this channel 500 yds from the bridge and by this time it has already turned into the bridge support

The tidal range that day was 1 ft so I do not see much effect due to this factor.

This is the video and chart I used to form my opinion. There is obviously information we do not know. I still believe the captain tried to stop the ship as seen by the black smoke pouring out until the ship hits the bridge.



https://www.charts.noaa.gov/OnLineViewer/12281.shtml

 

[sophiecentaur]

Channel bank suction effects and prop walk, both at low tide,

The nearest experience I have of this sort of effect was in a sixty foot canal narrow boat - not dissimilar shape. The channel bank suction aeemed to be a surface effect. You could see the bow wave following between a well defined bank (vertical canal sides) and the hull and you had to correct for the suction (unstable course) as you went close in. I have a feeling that a shallow dredged Vee channel would not necessarily talk as much. At low tide, the effect would be more, of course. But we'd have to wait for the experts to pronounce on that. At this stage, it's not much better than idle chit chat (fun though it can be).I can imagine what the lawyers would do with what we have to say.

 

[nsaspook]

Nice stills and videos.

 

[Baluncore]

Unless something is changing rudder corrections are not needed when running down a straight fairway.

Are you saying that because the channel is straight, they did not use the rudder, and it could not have been making a slight starboard correction, at the moment they lost rudder control?

 

[Borg]

Nice stills and videos.

About 10 minutes in, he shows close-up pictures of the bridge that someone took while on a Carnival cruise. I passed under that bridge in 2013 in the same way. I need to see if I've got pictures of it also.

 

[Vanadium 50]

As for the ship, the lesson learned here is that such ships need to have independent systems to ensure navigation/steering/rudder control in the event that the main power plant (or whatever systems provides power to the navigation/steering system) shuts down.

Is this realistic?

The rudder works in conjunction with the main engines. It redirects water flow, providing a force. If the main engine is down, the rudder becomes much less effective.

There are aux engines, but as I understand it, they are too small to drive the ship, and in any event, are not hooked up to the shaft. Do we require ships to carry two complete redundant engines?

Further, what about damage to the rudder itself? Maybe that wasn't what happened here (but maybe it was), but it could happen. Do we require multiple rudders as well as multiple engines?

You are familiar with another sector, where one technology has been made two to three orders of magnitude safer than its predecessor. Unfortunately, the reaction of most of the public has been "it's too expensive".

 

[Rive]

Is this realistic?

I think thrusters could provide limited redundancy, if the auxiliary/emergency generators are big enough and are online during sensitive operations.
Speed limits and capabilities should be matched and requirements updated, but 'feels' doable.

 

[Vanadium 50]

Thrusters, despite the name, have almost no thrust. They will not get a ship to 7 knots, and so they will not stop a ship at 8 knots. They are good for "fine tuing" as a ship is docking, but not for, for example, getting out of the way of a bridge.

Technically, this is a solved problem - go to diesel-electric. Diesel turns a generator, which powers the motor, which turns the shaft. Now your auxiliaries can do the same thing. This is a lot more expensive, and it's not clear it's even helpful, because now there are more things to break down.

It's also less efficient, which means higher costs. Global shipping is a $200B a year business. Knocking down a bridge that takes $2B to fix is a 1% perturbation. A 10% hit on fuel economy to prevent this makes no economic sense.

Further, 10% more fuel means 10% more pollution. Is that a good idea?

 

[Swamp Thing]

Another propulsion loss situation while leaving port... Also, fuel issues on Dali

 

[Borg]

It's also less efficient, which means higher costs. Global shipping is a $200B a year business. Knocking down a bridge that takes $2B to fix is a 1% perturbation. A 10% hit on fuel economy to prevent this makes no economic sense.

I was thinking the same thing with respect to the pier supports. Upgrading all of the supports around the world to account for the much larger ships would probably be equally costly. But, when there is only one major hit around the world every decade or so, the ROI doesn't work out well.

I find it interesting that there is a tunnel portion of the bridge outside the naval base in Norfolk VA. I guess the military doesn't want its ships trapped by a bridge collapse.

 

[PeterDonis]

I find it interesting that there is a tunnel portion of the bridge outside the naval base in Norfolk VA. I guess the military doesn't want its ships trapped by a bridge collapse.

There are actually two tunnels under the channel from the Norfolk naval base to the ocean: the Hampton Roads tunnel coming over from Hampton/Newport News, and the southern tunnel of the Chesapeake Bay bridge-tunnel that comes over from the Eastern Shore. I don't know that bridges high enough to accommodate shipping traffic (there is plenty of commercial shipping going in and out of Norfolk too) would have been feasible; even the shorter span, the Hampton Roads one, is, IIRC, significantly longer than the span of the Francis Scott Key Bridge.

 

[Vanadium 50]

I've been through that tunnel. It is a serious tunnel.

 

[Rive]

Thrusters, despite the name, have almost no thrust. They will not get a ship to 7 knots, and so they will not stop a ship at 8 knots.

They don't have to. To steer a ship what you need is lateral trust at stern or bow (or both, in opposing direction). The rudder at the stern (in the way of the flow of the main engine) means just a convenient, efficient mean to have that thrust, and never, ever had the need to get the ship at 7 knots or anywhere.

I don't know how the thrust of those thrusters and the thrust of the rudder relates, but you don't want to waltz sideways with a container ship anyway. It's just about a possible alternative, redundant steering method.

 

[gleem]

Bow thrusters provide lateral thrust and are used to maneuver ships in tight quarters.
See https://www.marineinsight.com/marin...he power of the bow,(11 knots) while berthing. for details

 

[Rive]

In case/as long as it's accounted as reserve/emergency steering in difficult areas, but with main engine operating the relevant diesel generators should be kept online => different approach than standard operation, but yeah, that's it.
So to get redundancy in steering is not that big issue.

 

[Borg]

About 10 minutes in, he shows close-up pictures of the bridge that someone took while on a Carnival cruise. I passed under that bridge in 2013 in the same way. I need to see if I've got pictures of it also.

Found one but from a distance.

Sept. 2013

 

[Vanadium 50]

A bow thruster has maybe 4% of the thrust of the main engines. That's the equivalent of 2 or 3 degrees of rudder at full power. "Full rudder" is 30 degrees. So you can see they are really not effective at steering, and really really not effective at stopping.

The harbor pilots know their job. If it were as simple this, they would have done it.

Could we fit ships with ten bow thrusters? Sure. But this runs into very similar practicality issues as the ones I discussed earlier.

 

[Flyboy]

This is, hands down, one of the most unlikely failures I’ve heard of happening at the worst possible moment. I think trying to redesign or refit ships to compensate from this one particular failure is overkill. Faster, cheaper, and easier to run a pair of tugs as escorts until clear of the bridge. I strongly suspect that even one tug pushing against the bow of the MV Dali would have been enough to steer it away from a direct hit. Might have been run aground, but it would not have hit the bridge.

However, that is with the benefit of hindsight. We’re armchair accident investigating, which is at best pointless, and at worst actively harmful.

I’m going to wait for the official reports to come out and see what the actual experts suggest.

 

[Vanadium 50]

one of the most unlikely failures I’ve heard of

This usually happens when there is a common point of failure taking down the allegedly redundant systems. For example, one thing that could take down all the diesels at the same time would be a fuel problem. There are probably others.

This is why you are hearing some pushback from me on the idea "we need more redundancy!". If the failure was a common element of all the redundant systems, adding more redundancy does not help.

Also, things always seem like better ideas when someone else bears the cost. Let's imagine this was a fuel problem, and occurred when the fuel was being switched over (or prepared to be switched over - it seems a little early for the switch). Cargo ships carry two kinds of fuel - expensive, low-sulfur fuel for use inb harbor, and cheaper, regular fuel for everywhere else. This sounds like a good idea to the general populace "Less pollution, and the shipping companies are the ones who have to pay for it." Until a bridghe goes down. I am not saying this is what did happen, merely what could happen.

 

[Baluncore]

I agree, bow thrusters are not a solution.

So you can see they are really not effective at steering, and really really not effective at stopping.

When moving forwards, the bow thruster duct is inefficient. The bow thruster cannot draw in sufficient water to be effective for steering.

Could we fit ships with ten bow thrusters?

Bow thrusters are driven by hydraulic motors, powered from the electrical system. An electrical blackout defeats bow thrusters, and there is insufficient electrical power to run more than one bow thruster.