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.