Dali Engineering Aspects - various and sundry

You have a much much smaller transformer that you close across from the HV side to energize the secondary side of the main transformer to pre-magnetize the core, prior to closing the primary HV feeder breaker to the primary side of the transformer. It almost completely eliminates inrush current and should greatly prolong the life of the transformer and the breaker.

The more complicated version has been in use on some drillships for over a decade, but I’d think the ROI is definitely there for a simplified version on something like a cargo ship bow thruster transformer. It also means you can place online without needing an extra generator.

Just wondering if this is actually used in that industry too now?

I’m familiar with the AKA version (again, built to a level not generally needed on a regular cargo vessel, but there’s a diagram in the PDF linked on their webpage)


My preconceived notion.
If anyone here happens to guess correctly what occurred. Probably just a coincidence. Hence my reluctance to propose any theories.

Why would turning machinery off cause a blackout?

These are worth their weight in gold! Standard issue on the new generation of the FPSO’s in my previous life. 11K board. (The system employed was to charge/mangetize the secondary windings). On the Dali they probably have 12-14 of these transformers for the reefers and a couple of the MSB. Definitely a case to be made to retrofit … irrespective of this unfortunate event.

Indeed off topic. A VFD and a motor that is ‘VFD rated’ adds a lot of complexity for a vessel with only 1 electrician.

I don’t really believe it adds much complexity. They’re fairly easy to deal with.

To weigh in on the whole shutting down the transformer thing. Unless I knew we were going to be down for a while I would not open the breaker feeding the xfmr.

Magnetizing inrush on a transformer can be somewhat random as well.

I think without any details of the electrical installation on board, it’s ALMOST pointless even discussing potential causes. We have so little information. It is fun though.

I did just have a very similar fault though. Relay was never commissioned properly. many possibilities.


Agree … easy to operate. Troubleshooting and maintenance requires specialized talent.

Hello all
I watched Sal’s latest video a couple of times where he provides updates from the VDR along with the vessel track from the AIS. Some interesting observations that was not noticed earlier, such as there were 3 blackouts and the vessel bow moving to port seconds before the impact. Timeline from the video. Not sure if the time between the AIS/VDR/CCTV are sync’d – so will provide the times below on the vessel issues

01:24:33 First blackout. Course/speed 141/8.5 (On another video we observe the lights flickering before complete blackout)

01:25:31 Lights comes on. 58 seconds. Quite a few deck lights and not likely these are fed from the ESB, so probably from the MSB. A slight wisp of smoke can be observed around this time (auto or manual start of another engine). Cannot make out if running lights came on before this. Let’s also remember that the exhaust from the EDG will not be in the funnel. Actual location and capacity of EDG is unknown at this time – definitely not a truck engine – more like 400-500 kW.

At some point in between lights on above and blackout below, thick black smoke observed from the stack. I think this is the main engine running astern.

01:26:37 Second Blackout. 65 seconds after lights come on – more on significance of this below

01:27:04 Anchor drop order from the Wheelhouse.

01:27:11 Lights on again. Main engine started again shortly after (within a few seconds)

01:28:30 Vessel starts swinging to port (left)

01:28:45 Impact. Black out looks like a few seconds before Key Bridge collapse. (Approx 70-80 seconds after lights on)

In port information: Reports of ‘blackout’ from reefer containers loading team. Was this complete blackouts with DGs tripping or was it only reefer circuits tripping? Information to be confirmed.

NTSB advises ‘circuit breaker’ faults are the primary cause and have requested Hyundai engineer to assist with the investigation.

Considered opinion:
With the vessel info we have so far that was mostly noted from this forum with people digging up information,
While it is not a 100% confirmed, I think this vessel (similar to many of the large container vessels) is equipped with a high voltage (HV) system. Could be standard voltages of 3.3 or 6.6 or 11 kV (Kilo Volts).
On a HV design system, Diesel generators are producing HV and connected to a HV board. The HV board will provide power through transformers to the MSB (main switchboard) and several transformers to power the reefers. Vessel is equipped with 1400 reefer plug outlets. So possibly 10 – 14 transformers with each transformer feeding 100 – 140 outlets. Then there is the Bow Thruster rated at 3000kW. Makes most sense that the motor will match the HV bus voltage. Power to each of the reefer transformers will be through a separate circuit breaker on the HV board. In the case of the BT, the circuit breaker will actually feed a motor controller that in turn is connected to the BT motor with cables running all the way to the BT space. I am assuming this BT is single speed motor and a CPP (as opposed to VFD and FPP).

After a blackout, the reefer loads (feeder circuit breakers) on the HV be designed to be switched on sequentially such that the generators are progressively loaded. The duration for this sequence could be about 2 minutes or so. The feeder to the MSB most likely will have no time delay and come on immediately as the MSB may have a sequential program as well built into the design.

So, after the lights come on after the first blackout, we have a second blackout about 65 seconds later. Is this during sequential loading of the HV board with the reefer feeders coming on and we have a bad actor that trips the board? Possible. Note that it happens again. Lights on again and what looks like about 70-80 seconds later blackout again possibly due to the same defective breaker.

What about the first blackout? What could have caused this if everything was in steady state operation? What about the lights flickering … does not happen on the subsequent blackouts? I had earlier theorized that the timing of the first blackout could be coincidental to the Wheelhouse advising they are done with the BT. Is it possible that while securing the BT, either the motor contactor or the circuit breaker does not open as designed and ‘chatters’ and creates fault leading to the blackout? Does this ‘chatter’ manifest in light flickering? Possible.

I had earlier speculated that the wheelhouse had requested the BT again close to impact and possibly this was the cause of the second blackout. But I now think BT came on and the last bit of the vessel bow turning to port is indicative of this.

So then, what about the steering? During a blackout, the steering will fail in ‘last position’. Was the rudder a few degrees to stbd? Or was this the Curtis bay water pushing the stern. Both are possible. But I think the blackout damaged the steering gear and was hydraulically locked. Position unknown.

Assuming there was no human error, the concurrent and consequential cascading failure can only be termed as a freak accident. Would be good for the NTSB to release some findings shortly such that responsible operators revise their standard operating procedures.


The bow thruster is 3000hp (nominal transverse thrust of approximately 30 tonnes whilst stopped in the water). At the speed of impact and immediately prior, at the part loaded draft of 12.2m, the bow thruster would have been completely ineffective. I would be very surprised if the experienced Pilot made this request although ……and I will go out on a limb here……perhaps this request, if indeed it did occur, came from the Master.

Hello Aus
You may be very well be right … with the chaos in the wheelhouse I think they might want to reach out any available means at their disposal.
On another note, I do not think the vessel speed would be close to 7 kts at impact. If this was the case the Key bridge structure perhaps would sitting further aft. Maybe the vessel slowed down to closer to 2 or 3 kts. Just saying and thinking out loud.

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Hi Aus,
I must say I agree with Mr Retired engineer here.
I don’t think it matters how effective a BT may be at 7 ISH KTS , I think I would have tried it anyway.
Hence I would have asked for it to be started and operated at full power to port.
Anything in extremis.


And you may be correct and again in extremis the Master would try anything


And on the issues of Bow Thrusters,
Never really liked them on large ships but in this case, shame she didn’t have a stern thruster as it would have been much more effective



Absolutely agree and the analogy could be aligned with the use of anchors in this instance.

On that note, the inconsistency of naval architecture as governed by building budgets with regard to thruster capacity is frustrating. The 3000hp thruster fitted to the “Dali” (300m LOA) is equivalent to half an ASD tug. The twin 3400hp thrusters fitted to the “Ever Given” (400m LOA) is equivalent to one ASD tug yet a modern day 365m LOA passenger vessels with similar high windage are fitted with in excess of 30,000hp bow thruster capacity equivalent to five ASD tugs and 90,000hp in azimuthing stern propulsion. I used to inwardly smile at the arrogance displayed by some of the passenger vessel Masters that I worked with. It would be interesting to see them handle a 400m ULCS with 6800hp up front and nothing down the back……….
The passenger vessel will be a $2 billion build and the ULCS a $120m build.


Absolutely agree and the analogy could be aligned with the use of anchors in this instance.

Absolutely agree

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With regards to cruise ship masters,
Yeah wonderful thrusters.

Just how good are they in a 5 KT current?

Remember having a conversation with a master that didn’t want a forward tug when he had an x??? Size BT .

How effective is your BT when we are doing 2 kts stw and the tide is ebbing at 4 kts
Use your BT , which way Mr pilot? Anyway you like sir it’s going to have no meaningful effect

Sorry we are now hijacking a very interesting engineering thread.

Hello Aus and 244
On the cruise ships the 30K BT is not a tunnel thruster. These are the azipods with the motor inside the pod. Stern has 2 of these, and looks like the vessel can be turned on a dime. I think these are great inventions. And yes some Masters can be you know what - sailed with a few! A cruise ship master on a ship like Dali reminds of the Heinz baked beans commercial - ‘not for astronauts’ :slight_smile:

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i may of missed it but operating in confined waters I am sure they would of had two gen sets on he buss, idk if that’d be enough to run a 3K hp BT along with everything else?