Dali vs. Aleta

Position: 39°13’00.9″N 76°31’40.1″W

A bit of maritime history was made this week when the appropriately named bulk cargo carrier MV Dali crashed surreally into the Francis Scott Key bridge just outside Baltimore Harbour. Unless you were living under a rock, you should by now have seen the footage of the spindly bridge toppling over like it was made from matchsticks. The ship was making about 6.5 knots at the time of the accident. Aleta sails at 6.5 knots in good conditions. Had we struck the bridge in the same place going the same speed, I would hope our life jackets would have inflated as Aleta sank gently into the soft Chesapeake mud. On a slow day we might have made the news cycle.

There’s nothing particularly distinctive about the Dali. She’s a bulk-y carrier that we could spot about seven miles away at sea. At two miles distant she would look huge and imposing and I’d want to make sure our courses never crossed. At a young age I learned things don’t happen quickly at sea, until they do. With that in mind, let us compare Dali and Aleta’s specifications:
In short, Dali is 25 times longer, 12 times broader, and needs 8 times more water under her keel as Aleta does. Yet, she only makes three times Aleta’s hull speed. Why, you ask? Perhaps you already know.

Physics

This early version of a scene from The Graduate helps sum up the differences between Dali and Aleta:

Mr. McGuire: I want to say one word to you. Just one word.
Benjamin: Yes, sir.
Mr. McGuire: Are you listening?
Benjamin: Yes, I am.
Mr. McGuire: Physics.
Benjamin: Exactly how do you mean?
Mr. McGuire: There’s a great future in physics. Think about it. Will you think about it?^[1]

If you went to high school, you probably took physics. I did. In my freshman year. Carol avoided it somehow. About the only thing I remember, besides the fun of dropping little toy cars down an inclined slope with a bit of tickertape tied to them that a mechanical device printed dots on so we could measure and calculate acceleration, is Force = mass x acceleration (F=ma). That’s it. All the rest is consigned to my mental midden. I doubt even a heroic dose of psilocybin could disinter that particular knowledge from all the sediment and detritus laid down over the past 50 years. I’m sure it’s in there. I just can’t voluntarily access it.

Math

Okay, let’s do some math. Before we do, a disclaimer: engineers, scientists, and mathematicians are bent on getting the correct answer. Marketing folks are bent on telling a story.

MV Dali is roughly 6,342 times heavier than SV Aleta. She can also carry 9,900 20-foot equivalent shipping containers for another hundred thousand tonnes of mass. Now, I’m not going to pretend I fully understand all the calculations that go into gross, net and deadweight tonnage, but in marketing speak (something I have more experience with) the difference in mass between the two vessels is a bone fide ‘metric f*ckton’.

To estimate the Dali’s impact force, I naturally turned to Copilot, Microsoft’s AI helper, for the calculations^[2]. Here’s what it said: “The force exerted by the ship on the bridge was approximately 100.3 million Newtons.” That’s about 24 tons of TNT. Clearly enough to topple a bridge. If Aleta had hit the bridge with the same variables, we’d have expended about 8,600 Newtons, or a couple of M80s-worth of energy.

A-damn Smith

There is of course a bigger story here. One with a tragic loss of lives that might have been much worse if not for the quick thinking of the bridge’s work crew. From there we might examine the burgeoning use of gigantic cargo ships, the general lawlessness of international shipping, and the tragedy of the commons that the oceans have become.

Let’s put that to one side for a moment. Let’s consider all the unseen work that goes into making our lives livable in the modern world. The invisible workers filling potholes in the middle of the night. The crews of ships leaving port to sail halfway around the world on journeys that might keep them away from their families for months. Then there’s the hard work of the rescue services doing their best in the most difficult circumstances. These are the invisible hands that keep the economy running. If you are short of an argument for redistribution, you might start there.

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[1] (For the record, I think Buck Henry was right to go with “plastics”.)

[2] “To calculate the force exerted by the cargo ship Dali when it collided with the Francis Scott Key bridge, we’ll use Newton’s second law of motion, which states that force is equal to mass times acceleration (( F = m \times a )). First, let’s convert the ship’s speed from knots to meters per second (m/s). One knot is approximately equal to 0.51444 m/s. Therefore, 6.5 knots is: [ 6.5 \text{ knots} \times 0.51444 \frac{\text{m}}{\text{s per knot}} = 3.34486 \text{ m/s} ]

Next, we calculate the acceleration using the formula ( a = \frac{\Delta v}{\Delta t} ), where ( \Delta v) is the change in velocity and ( \Delta t ) is the change in time. The ship decelerated from 3.34486 m/s to 0 m/s in 5 seconds, so: [ a = \frac{0 \text{ m/s} – 3.34486 \text{ m/s}}{5 \text{ s}} = -0.668972 \text{ m/s}^2 ]

The negative sign indicates deceleration. Now, we can calculate the force. The mass of the ship is given as 150,000 metric tonnes, which is 150,000,000 kg in SI units. Using the formula for force: [ F = m \times a ] [ F = 150,000,000 \text{ kg} \times -0.668972 \text{ m/s}^2 ] [ F = -100,345,800 \text{ N} ]

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