Baltimore Francis Scott Key Bridge collapse

[dietert1]

I found this info on thrusters:
https://www.marineinsight.com/tech/bow-thrusters-construction-and-working/

They say:
"Bow thrusters are generally used to maneuver the ship near coastal waters and channels or when entering or leaving a port during bad currents or adverse winds.
Bow thrusters help tugboats berth the ship to avoid unnecessary time and, eventually, money wastage because the vessel stayed less in the ports. The presence of bow thrusters on a vessel eradicates the need for two tugs while leaving and entering the port, thus saving more money."

So i don't understand what is meant by a bow thruster being ineffective. Where does this idea come from?
I estimated a bow side-shift of about 27 m after running a 4 MW thruster for 180 seconds.
It's a fact that the hazard occurred after midnight when everybody needs a rest.
The question i asked will be asked anyway. There will be enormous legal fights about this. They caused a tremendous hazard and killed six people.

Regards, Dieter

[soldar]

You are out of your depth here.

[Andy Chee]

A bit of trivia:

Looks like Google Streetview has stopped "travel" over the Francis Scott, despite being intact in cyberspace!

https://maps.app.goo.gl/EQ9Q9w5jR4qMU5KS7

[Andy Chee]

I estimated a bow side-shift of about 27 m after running a 4 MW thruster for 180 seconds.

No power.

[JustMeHere]

It is a bit odd design with the main motor shutting down even with a rather short interruption of the generators.

The engine will stall if the blowers are not running.  The engine cannot breathe on it's own at low power.

[ArdWar]

Two stroke diesel can't breathe on its own at all. If its scavenge air blowers stop the engine stops, period. The blowers are integral part of the engine operation cycle, unlike 4 stroke engine.

However at most operating range other than very low load (<25%) its exhaust should be enough to self sustain the turbocharger without needing auxiliary powered blower.

[dietert1]

I estimated a bow side-shift of about 27 m after running a 4 MW thruster for 180 seconds.

No power.

Read preliminary report. From first electrical problem to crash were about 5 minutes with two outages of about 1 minute each. That's why i assumed 3 minutes = 180 seconds.

[Ice-Tea]

Read preliminary report. From first electrical problem to crash were about 5 minutes with two outages of about 1 minute each. That's why i assumed 3 minutes = 180 seconds.

* You don't use a bow truster at that speed. Good chance the controls are labelled to avoid some clown to try that anyways.
* You don't launch a 3MW load on an electrical net that is already troubled. In other words: the occurance of the second blackout was unexpected and unlikely but you would increase the chances of it occuring by an order of magnitude by launching the bow truster.
* After the second blackout, power was restored but only DG2 was running. Launching the bow truster at that time would have caused a guaranteed fresh blackout.

There are very few things you can do on board such a ship that would cause a blackout under normal conditions. Running the bow truster with an unprepared ER is one of them.

[soldar]

* You don't use a bow truster at that speed. Good chance the controls are labelled to avoid some clown to try that anyways.
* You don't launch a 3MW load on an electrical net that is already troubled. In other words: the occurance of the second blackout was unexpected and unlikely but you would increase the chances of it occuring by an order of magnitude by launching the bow truster.
* After the second blackout, power was restored but only DG2 was running. Launching the bow truster at that time would have caused a guaranteed fresh blackout.

There are very few things you can do on board such a ship that would cause a blackout under normal conditions. Running the bow truster with an unprepared ER is one of them.

Furthermore, from the plan shown in the preliminary report, it seems the Dali started veering to starboard only after the second power failure.

The report says:

The loss of electrical power stopped all three steering pumps, and, therefore, the rudder was unable to be moved. At the time, the ship was on a heading of 141.7°, a course over ground of 140.8°, and speed over ground of 9.0 knots, with the rudder amidships (0°).

At 0126:02, the VDR, which had stopped recording vessel system data when the blackout occurred, resumed recording the data. The VDR audio recording had not been affected by the blackout. The Dali’s heading was 144.3° and course over ground was 142.7°. Its speed over ground was 8.6 knots. The apprentice pilot called the pilot dispatcher by mobile phone. At 0126:13, the senior pilot, who had regained control from the apprentice pilot by this point, ordered 20° of port rudder.

The discrepancy between the ship's heading and COG, Course Over Ground, indicates the effects of currents and winds which are very changing in that area.

We will have to wait to find out why the electric power failures but it seems to me the crew were first class and acted decisively, promptly and professionally.

Anyone who thinks they know how to do better just does not understand the magnitude and complexity of the problem.

It seems the ship had been running on trafo #2 for months without problem and due to a mistake made by a crew member while in port they decided to run on trafo #1. It could be unrelated but there is a good chance this is the root of the problem and what triggered the whole incident. It will be interesting to see what comes out later.

[dietert1]

They write the circuit breakers of the two generators 3 and 4 tripped when the second blackout happened. They don't say the  generators stopped. I understood they had three HV generators and the LV emergency generator running. If necessary they could have used the fourth generator, too.
About not using a bow thruster at slow speed: We should not substitute reasoning by calling other people names.

Regards, Dieter

[Ice-Tea]

The clown remark was aimed at a hypothetical deck officer that would need a reminder not to use the bow truster above a few kn, not you.

Once again, you don't launch the bow prop if the ER is unprepared or, worse, recovering from a blackout. That is how you create accidents, not how you avoid them.

Note also that the NTSB report doesn't even mention the availability of the bow truster. It would seem that for them, it's not even a topic as there is no expectation or desire to have that as an option.

When the breakers for DG3 and DG4 tripped there was a reason for that. They may have been overloaded (in which case adding a huge additional load on the bus is kinda bad) or the DGs themselves may have experienced propblems causing speed and thus bus frequency to drop (which would make them too unreliable to put back on the bus).

And no, they could not have quickly started DG1. That one was not in standby.

And even if by some miracle there was a minor window in time where they could have reliably used a magic truster that works at higher speeds, then this would have been known in the ECR, not on the bridge.

[NiHaoMike]

What other large loads are there on the HV bus besides the bow thruster? Seems like it would have made more sense to have the bow thruster be hydraulic and use HVDC for the electrical system.

[Ice-Tea]

Probly only power distribution to reefers.

[coppercone2]

I mean can't a black out be caused by anything like sticky breakers and some short that burned itself out? if that is the case then so long it mostly cleared itself you can try to run the thing full power right away. there is a chance the trouble is at that point completely isolated (vaporized wire somewhere)

there is always a chance like a small breaker will fail, the load will be vaporized, the big breaker will trip. but after that its irrelevant like nothing was ever there.... the problem is isolated and you can run the circuit at its 100% capacity or even more since that load is gone

i mean its a shady condition and you wanna get that checked out right away but if your gonna crash you might as well try

[mendip_discovery]

From the chats I have had with a friend who spent most his life fixing big boats. He would always complain about the lack of spending, if there was a problem they would work around it until it was a big problem or they could dock somewhere where the labour was cheap enough, a bit like not going to the main dealer for a service but using a local independent.

I did lol at a bbc news article the other day that had the headline Boat Crew still Stuck on board. They were planning a long trip anyway but I think it was a slow news day and a reporter needed to up their word count.

[Ice-Tea]

I mean can't a black out be caused by anything like sticky breakers and some short that burned itself out? if that is the case then so long it mostly cleared itself you can try to run the thing full power right away. there is a chance the trouble is at that point completely isolated (vaporized wire somewhere)

* There probably wasn't enough power after the first blackout
* There was no reason to even try after the first (heading)
* There surely wasn't enough power after the second blackout
* Restoring propulsion would have been orders of magnitude more effective, so why waste time and effort on that.

[AVGresponding]

What other large loads are there on the HV bus besides the bow thruster? Seems like it would have made more sense to have the bow thruster be hydraulic and use HVDC for the electrical system.

And how would you power the hydraulic pump that drives your hypothetical hydraulic bow thruster?

[NiHaoMike]

And how would you power the hydraulic pump that drives your hypothetical hydraulic bow thruster?

Mechanically from the auxiliary engines.

[ArdWar]

Mechanically driven "Z-drive" bow thrusters are pretty common. Its just that it's uncommon for this kind and size of vessel since it requires placing a diesel engine at a remote location, which also requires engineer to attend during operation. Hardly any safer, and importantly more $$$ to operate.

Hydraulic driven bow thruster (actual hydrostatic drive, with pump-motor pair) also exist(ed). It just that it's probably not exactly what you want since the hydraulic line is only used to bridge the small gap between thruster hub and ship hull. You still need a diesel engine or electric motor close by to run the pump which doesn't exactly simplify things from how it is currently done.

[Ice-Tea]

Chief Makoi on the NTSB report: