Master Helmsman's Take On The Baltimore Bridge Incident

Was it an accident or was it intentional?

I'm a certified master helmsman with years of experience. I've been studying the Baltimore bridge collapse situation for a while now and I keep learning new things every time I rewatch the video and study the harbor track. My theory of how this happened has undergone a few changes.

The Dali was completely without power for about one minute and thirty seconds. The first power outage lasted about one minute and the second lasted about thirty seconds.

Due to the way rudder hydraulics work, we can assume the rudder was locked in the last position the helmsman had it in each time the power went out.

I've tried several scenarios in a professional ship simulator using a similarly sized cargo vessel, seeing what it would take to replicate the incident. I find that it requires around 20 degrees or more of rudder input to get similar turn rates as the Dali experienced. To me, 20 degrees is too much to be using during a standard course correction, so I don't think rudder input alone explains this.

I think the most important factor in this incident is actually a phenomena called bank suction. Bank suction is caused by the Venturi effect as the ship transits near the underwater bank of the channel. It can be very powerful.

As the Dali was transiting the Fort McHenry channel close to it's port side when it lost power, the bank suction effect could have pulled the stern toward the bank and pushed the bow to the starboard side.

If you couple the bank suction effect, along with a cross channel current coming from the Curtis Bay channel that joins the Fort McHenry channel right where this incident occurred, which could have directed a current right into the starboard aft quarter of the Dali, you could get a good amount of turning moment without any rudder input at all.

Now if we assume that during the initial one minute power outage the rudder was locked 10 degrees to starboard simply because of bad luck while the helmsman was correcting course, along with the bank suction effect and the cross current, you could get a very large turning moment even though the rudder input might only be 10 degrees to starboard.

When the power comes back on the first time, they might have been able to save the ship if they immediately threw the rudder over hard to port, but watching the video, I think the helmsman only put in about 10 degrees of port rudder (if any). It’s also possible they may not have regained rudder control at all, as the turn to starboard continues right up to just before the moment of impact. The rudder turns slower under emergency power, taking around thirty seconds to traverse full deflection.

So the power goes out a second time for thirty more seconds, leaving the helmsman unable to increase the rudder hard to port for an additional thirty seconds. This sealed the ship's fate.

So to sum up, bank suction, cross current, and insufficient corrective rudder were to blame for the turn into the pier. Obviously the entire incident was precipitated by the loss of power to steering. This is my current theory, subject to revision upon discovery of new evidence of course.

I don’t think this was intentional, at least not without evidence of sabotage. If a nefarious actor was intending for the ship to hit the pier of the bridge, knocking power out to the ship is the last thing you’d want to do. Without steering, there’s no way to intentionally direct the ship into the bridge.

We need a full investigation of why the power went out and why it took so long for backup power to be restored. The Dali’s backup generator should have kicked in within thirty seconds and restored power to steering if it was configured correctly.

This video discusses a similarly sized ship’s emergency backup generator and how it operates:

Commonly asked questions:

Why is there two minutes of missing data on the data recorder?

Only the voice recorder had a battery backup. The data recorder was tied to the ship's power, which explains why it's missing around two minutes of data. It's not unusual for it to be setup this way because if there is no power, nothing is working anyways, so there's no commands to record.

Why were there no tugs escorting it out of the harbor?

Tugs were used just to pull her out of the pier. This is completely normal. Tugs typically do not follow a ship out of the harbor. In this case, the ship was already beyond the point where tugs were required. Two pilots were on board at the time. Whether or not there was pilot onboard at the time really doesn't matter in this case, since without steering, there is nothing that can be done. Taking tugs along can actually pose additional risks, such as the tugs being dragged under due to the massive momentum of a ship Dali’s size moving at speed.

Why didn’t they drop the anchor?

Anchors on ships need to be manned. Dropping an anchor is a completely manual operation requiring no power. The pilot did order the port anchor to be dropped, and from the daylight photos, we can see that the port anchor is indeed in the water.

Anchors are designed to hold a stopped ship in place. They are puny and insignificant against the massive forces created by a ship the size of Dali moving at over 8 knots. Dropping the anchor likely did very little to slow the ship in such a short amount of time.

Anchors actually hold ships in place by the weight of the anchor chain. The anchor itself is merely there to help drag the chain to the bottom. Looking at this image of the Dali, we can see just how small the chain is in proportion to the size of the vessel.

To put it in perspective, the anchor and three shots of chain probably weight somewhere around 50 tons. The Dali itself has a displacement of 160,000 tons.

Why didn’t they just throw it into reverse?

Ships with fixed props like the Dali typically have a direct drive to the engine, meaning they typically have to stop the engine completely, engage reversing gears, then start the engine back up in the opposite direction before it can be reversed. It’s unclear if this occurred or if Dali had a different reversing system. Normally this entire process can take up to nine minutes on average.

What’s the black smoke plume from?

Typically this is caused by a light-off of the main engines. Compressed air is blown into the engines to start them, resulting in a large black plume of smoke. It can also be caused by a sudden spike in engine throttle. The loss of power could have closed engine intakes, which would have resulted in the engines automatically shutting down. The black smoke could be a sign that they were attempting to relight the engines.

This is the full video of the incident that is in real time. Most of the videos of this incident are artificially sped up: