Blog 133 - Updates on the mv Dali Affair - Analysis of NTSB Preliminary Report of 14 May 2024

The NTSB (National Transportation Safety Board) Preliminary Report was published on 14th of May 2024. My friend, Sudarshan Rajan was kind enough to alert me and send the complete report to me.

I am quoting only certain parts of the Report for brevity.

What you see in plain text is my input.

What you see in quotes are excerpts from the NTSB Report.

I could not resist adding - at the end - what I had conjectured to be the probable causes for the blackouts on the mv Dali that eventually resulted in the vessel colliding with the Baltimore Bridge, bringing down major portions of the structure and causing the deaths of seven persons. As per the conclusions of the NTSB Report, none of my conjectures came even close to their findings.

For background : 

The mv Dali can be considered to be a large ship, with some of the ship particulars as follows:

300m L x 48m W x 15m D (Length, Width and max Draft)

116,851 tons DWT x 9971 TEU capacity (Can carry 9971 Twenty Foot Containers).

My estimate is that 5% to 7% of the slots were for Refrigerated Containers, making a total of 500 to 700 Reefer Containers, each consuming 5 to 6 kw of power.

Main Engine 9 Cyl MAN B&W 9S90ME C9.2 (9 Cylinders: Each Piston Size (Dia) 900 mm)

41,480 KW - 55630hp - 82.5  rpm

Service Speed 22 knots

Bow Thruster 3000 kw (has a Bow Thruster which is strictly used only for berthing and unberthing) (Using a Bow Thruster eliminates the use of at least one tug - Tugs cost all over the world are prohibitive, $3500 to $5000 per hour on site, may be more these days).

2 Nos. 3,840 kw Generators

2 Nos. 4,400 kw Generators

The configuration of 6,600 volt alternators being stepped down through transformers is, nowadays, a common construct, as ships have become larger.

The Electrical Power Plant generation is necessarily high due to the size of the ship, consequently, the size of the machinery.  Carriage of Reefer Containers add to the power consumed.

440 Volt generators would have meant large sized generating machinery. By upping the voltage produced to 6600 Volts, the size of the alternator can be kept to reasonable sizes.

(Please note - the words ‘alternators’ and ‘generators’ - I keep interchanging them for convenience)

Unlike the smaller ships that had 440 volt Alternators, these 4 powerful alternators were 6,600 volt output ones. 

The Bow Thruster motor was a 6,600 volt motor.

Transformers stepped down the voltage to 440 volts for all machinery. 

Either a 220 volt or a 110 volt step down transformer would have been used for domestic purposes. (There is no mention of this anywhere).

Quote

1.2 Dali’s Electrical Power Distribution System

The ship’s electrical power was supplied by four alternating current generators, which were each driven by a diesel engine. Generator nos. 1 and 4 were rated for 4,400 kW, and generator nos. 2 and 3 were rated for 4,000 kW.

The generators were connected to a 6,600-volt high-voltage (HV) main electrical bus by the vessel’s power management system (see figure 3) that powered various shipboard equipment, including the main engine lubricating oil pumps, the bow thruster (a propulsor on the ship’s bow that that assists with ship maneuverability), and reefer containers

3 The HV main electrical bus could be split with an installed main bus tie (HVR in figure 5 on page 88), which would isolate two generators on each side of the bus. The bus was designed to be normally operated in a closed-bus configuration (meaning the main bus tie, which connected the two sides of the bus, was closed); this was the case during the accident voyage.

Figure 5. Simplified one-line electrical diagram of the Dali electrical power distribution system. Breakers shown reflect their positions at departure on March 26.

Below is the same circuit diagram but slightly more explanatory, author Chief Makoi, You Tuber.

Quote

About 0125, the Dali was 0.6 miles—or three ship lengths—from the Key Bridge

when electrical breakers (HR1 and LR1) that fed most of the vessel’s equipment and lighting unexpectedly opened (tripped) (see figure 7). This caused the first blackout (loss of electrical power) to all shipboard lighting and most equipment, including the main engine cooling water pumps (which controlled engine cooling water pressure) and steering gear pumps.

• Generator nos. 3 and 4 continued to run and supply electrical power to the HV

bus.

• Most bridge equipment also lost power, and the voyage data recorder (VDR)

Figure 7. The Dali’s route on March 26, between the first blackout, and the Dali striking pier no. 17 of the Key Bridge. The location and approximate size of two of the bridge’s “dolphins,” sheet pile and concrete structures protecting the bridge’s piers, are labeled in the lower Right.

The main propulsion diesel engine was independent of the vessel’s four diesel-

driven electrical generators; however, the loss of electrical power to the pumps

required for its operation resulted in the main engine being automatically shut down, and the vessel lost main propulsion, meaning its propeller stopped.

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°).

Unquote

My interpretation of the NTSB Report:

Referring to the modified circuit diagram of the power generation, the distribution line of the 6600 volt system, the step down transformers and the further distribution for various services:

The High Voltage (6600 v) Breaker HR1 tripped, along with the Low Voltage (440 v) Breaker LR1.

This caused a complete power loss to all sections.

The Main Engine tripped, as no power went to the Lub Oil Pumps and Cooling water Pumps - causing a complete loss of propulsion.

All the three Steering Pumps stopped - causing a complete loss of steering.

But both generators, # 3 and 4, had not tripped and continued to run, making us surmise that it was not a fuel related problem.

The combination of the loss of both propulsion and steering meant the ship was - for that period of time - completely uncontrollable. 

If this had happened after just a few minutes, she would have been clear of the Bridge and would have either run aground in the shallow waters or drifted till the power was restored to propulsion and steering.

Why the Breakers tripped is under investigation for, normally, they are trustworthy and have a maintenance cycle to detect any defects.

I had conjectured, wrongly, (with the chances rated at 90%) that the fuel (the vessel would have been running on Diesel Oil at that time)  was, most likely, contaminated with a high percentage of paraffins, which would have choked up the on-line filters.

Below is an image of such a type of filter on the Diesel Oil line.

Paraffins, being wax like, clog up the small micron sintered filters. No amount of auto (in situ) cleaning can remove this wax as it goes into the pores and chokes the filter. The only way to clean it is to dismantle all the elements and either ‘steam’ it or use a light flame - to melt the wax. I’ve had this happen to me twice while maneuvering and had nearly come to a stage where we could not give engines. As a last resort, we changed over to a previously used fuel that had not given trouble and saved the day.

The choking of filters would have caused a loss of fuel pressure to the generators, on which they would have either slowed down or stopped, causing a reduction of voltage and frequency, with which the generators would have tripped, causing a black out.

But the NTSB Report is specific in that the 2 running generators did not slow down or stop. Which means that the generators were generating power, but the power was not getting distributed due to the Breakers HR1 and LR1 tripping.

AR