Baltimore's Francis Scott Key Bridge Collapses after Ship Strike

[OmCheeto]

How big do you suppose the thruster motors are?

According to wiki "For maneuvering, Dali has a single 3,000 kW (4,000 hp) bow thruster."

That's about 3/4 of the capacity of one of its four 4 megawatt diesels. Going back to the original NTSB report, it does show the bow thruster being powered off of the 6600v bus. My bad!

 

[Nugatory]

Sure, but that's why engines have rev limiters.

I was going to mention that my 70’s vintage cars do not have rev limiters, but I was wrong. An out of control over rev situation is automatically corrected when a con rod comes out through the block.

 

[PeterDonis]

An out of control over rev situation is automatically corrected when a con rod comes out through the block.

So it's a "rev limiter" in much the same way as the ground is a "fall limiter"?

 

[Tom.G]

I was going to mention that my 70’s vintage cars do not have rev limiters, but I was wrong. An out of control over rev situation is automatically corrected when a con rod comes out through the block.

Or when you run out of oil on the Interstate Highway.

 

[renormalize]

Also, while I have zero knowledge of this type of vessel, it strikes me as very peculiar that the chief's schematic shows the 'reefer containers' and 'bow thrusters' running on 6600 volts. A quick google shows that these type of 'reefers' run on 440 volts, which would be more in line what I would suspect.

I think you badly underestimate the power requirements for thrusters on large ships. Below are some specifications for a fairly large vessel built to transport and deploy loads of rock that underlays submerged pipelines: (https://www.ingeteam.com/Download/2574/attachment/case-study-joseph-plateau.pdf.aspx)

All of the electric motors for thrust and propulsion provide multiple-megawatts of mechanical power and all run at over 3000V, so each draws currents of multiple-hundreds of amps. If they all ran at 440V instead, their draw would increase to multiple-thousands of amps each. Can you imagine the size of the conductors needed to carry that much current and the additional weight-penalty that the vessel would have to bear?

 

[OmCheeto]

Can you imagine the size of the conductors needed to carry that much current and the additional weight-penalty that the vessel would have to bear?

You are of course correct. I guess I should have done the maths after I found the actual wattage rating (Post # 281).

3,000,000 watts/6600 volts = 450 amps * 1 cable
3,000,000 watts/440 volts = 6800 amps ≈ 15 cables * 450 amps

I would love to see the control circuitry for that monster. I wonder how long it takes to get up to full speed. Might be a factor in the incident.

 

[berkeman]

 

[gmax137]

Your backordered part here

From the start, I was wondering about people who had their personal belongings in the containers - household property, antique cars or bikes, artwork, etc. etc. I guess if you're going to ship your stuff across the ocean you'd better have it insured for replacement cost.

 

[Vanadium 50]

It's complicated. There is something called "general average" in maritime law. If I am shipping $1M worth of stuff and you are shipping $1M of stiff, and yours is lost - say tossed overboard to save the ship - then I owe you $500K if general average applies.

If you have cargo insurance, then the insurance pays you $500K and I or my agent pays you $500K.

Of course in real life there are many shippers, many cargoes, many insurance policies. and this rule may apply in some cases and not others. Oh, and the lost cargo may be salvaged. This keeps the lawyers busy.

 

[gmax137]

. This keeps the lawyers busy

So has it always been...

 

[Astronuc]

AP News - Loose electrical cable found on ship that caused Baltimore bridge collapse
https://apnews.com/article/baltimor...-loose-cable-57c8260759fd313de006cf02bcf3ccfb

BALTIMORE (AP) — Investigators working to pinpoint the cause of Baltimore’s Francis Scott Key Bridge collapse discovered a loose cable that could have caused electrical issues on the Dali, the massive cargo ship that lost power and disastrously veered off course before striking the bridge.

When disconnected, the problematic cable triggered an electrical blackout on the ship similar to what happened as it approached the bridge on March 26, according to new documents released Wednesday by the National Transportation Safety Board.

The documents don’t include any analysis or conclusions, which will be released later in the board’s final report. A spokesperson for the board declined to comment as the investigation is ongoing.

Waiting for NTSB final report - https://www.ntsb.gov/investigations/Pages/DCA24MM031.aspx

 

[Vanadium 50]

I assume this is some kind of control cable and not the power itself? Those cables are...beefy. Really beefy. Not like a Taco Bell burrito. I couldn't find more details, though.

 

[OmCheeto]

I assume this is some kind of control cable and not the power itself? ...

Control cable connector. 110 vdc portion of an undervoltage trip circuit.

from page 39

I can't figure out how to link to the document directly, and it appears you can only read it if you download it.

41 pages. 1.1 Mb. Dated September 11, 2024: '...ort (download link) we ...'

Source of the link: https://maritime-executive.com/arti...ntsb-dali-investigation-could-cause-blackouts

 

[nsaspook]

That guy loose wire really gets around.

Brothers?