On March 23, 2021, the massive container ship Ever Given ran aground in the Suez Canal. The wedged vessel obstructed the entire channel, blocking one of the most important trade routes in the world for nearly a week. The cause and details of this event are still under investigation, but there’s a lot we already know. How could something like this happen, and why did it take so long to fix? I’m Grady and this is Practical Engineering. Today, we’re exploring some of the engineering principles behind the 2021 Suez Canal obstruction.

Before we get into the event itself, let’s learn a little bit about the Suez Canal. Built in the 1860s, the Suez Canal is a constructed waterway in Egypt, allowing shipping and other maritime traffic to go from the Mediterranean Sea to the Red Sea and vice versa. This means ships don’t need to navigate all the way north around the European and Asian continents or all the way south around the African continent to travel between the Atlantic and Indian oceans. It’s basically a global shortcut. That makes it one of the most important routes for global commerce, handling roughly ten percent of the entire world’s ocean trade.

For as important as it is to the global economy, the Suez Canal is a relatively straightforward structure: essentially a trapezoidal channel cut through the sand of the low-lying Suez Peninsula and taking advantage of the existing Great Bitter Lake at the center. Unlike the Panama Canal which uses locks to raise vessels up for transit, the Suez Canal is entirely at sea level with no gates or locks. Minor differences in level between the Mediterranean and Red Seas create gentle currents in the canal, but they’re not strong enough to trouble the ships. In 2016, an expansion to the Suez Canal opened, essentially doubling its capacity. The project involved adding a second shipping lane to part of the canal, and deepening and widening some of the choke points so larger ships could pass through. It’s now about 200 meters (700 feet) wide and about 24 meters (80 feet) deep.

All ships passing through the Suez Canal are required to have a Canal Authority pilot to help navigate each step. These pilots aren’t fully responsible for the safety of the ship during transit, but they have special knowledge about the processes, procedures, and challenges required to navigate these massive vessels through the canal. It’s tricky, and ships have been stuck in the canal before, including a 3-day blockage in 2004. So, each ship’s Master (sometimes called the captain) and the canal authority pilot work together to maneuver the ship through. It takes about half a day to get from one end to the other, and on average, about 50 ships make their way through the canal each day.

Navigating through the Suez Canal is a careful dance since some parts of the channel only have a single shipping lane with no room to pass. That’s why ships are required to go through in convoys. Early each morning, the convoys line up to enter the canal. The southbound group begins their journey from about 3AM to 8AM at Port Said, following the western channel. At around the same time, the northbound convoy enters the canal at Suez. On a normal day, everything is carefully timed so that the two convoys can pass each other in the Great Bitter Lake and the dual lane section of the canal without any stopping or interruptions. Unfortunately, March 23rd was not a normal day. One of the first ships in the northbound convoy, the Ever Given, had barely entered the canal at Suez when it veered into the eastern bank, smashing its bow into the sandy embankment and wedging the massive vessel diagonally across the channel’s entire width. Amazingly, there was not a single injury and the cargo was completely unharmed.

As I mentioned, the exact reason the ship ran aground is still under investigation. Some reporting suggested the Ever Given experienced a loss of power, but that was denied by the ship’s technical manager. Sources also say that there was an ongoing dust storm that morning creating high winds and limited visibility. Many have suggested that the Ever Given’s unscheduled and unfortunate landing in the canal may have been hastened by a hydraulic phenomenon unique to vessels transiting through shallow water called the Bank Effect. Before we explore this further, first a little info on this ship.

Leased and operated by international shipping company Evergreen, the Ever Given is one of the eleven Golden Class container ships, all confusingly named “Ever” combined with a seemingly arbitrary g-word. Weird names aside, these ships are truly massive. In fact, the Ever Given will never get a chance to go through the Panama Canal because it’s too long for the locks at 400 meters (or over 1,300 feet long). The ship’s beam is 60 meters (or nearly 200 feet) with a fully-loaded draft of 15 meters (or 48 feet). You can see how small the margin for error is with a ship this size in the canal.

If you remember your lessons on buoyancy, you know that a ship displaces its own weight in water. That means for every pound of steel and cargo aboard, a pound of water below the ship has to get out of the way. For the Ever Given, that is hundreds of thousands of tons of liquid being pushed to either side of the ship as it cuts through the water. On the open sea, that’s not a problem. The displacement forms a wake, but the water otherwise doesn’t have trouble finding a new place to go. In a shallow canal, though, things are a little different.

In a shallow canal, all the water displaced by a ship has to essentially squish through the small areas along the sides and bottom of the vessel. The smaller the area, the faster the water has to move to get out of the way. The water builds up at the bow (or front) of the ship. As the water accelerates through the narrow gaps on either side, its level drops. This is a well-known phenomenon that creates some unusual effects on ships. That’s because, in accordance with Bernoulli’s law, a fluid’s pressure goes down when its speed goes up. When traveling in a shallow area, the squished and sped-up flow below the hull creates a suction force pulling the ship further into the water, a phenomenon known as “squatting”. One massive ship even used the effect by speeding up as it went below the Great Belt Bridge in Denmark to create some extra margin above the deck. But, the exact same effect can happen on the side of a ship as well. If a vessel gets too close to the bank of a shallow canal, the water it displaces on that side essentially has nowhere to go. It has to pick up speed as it squishes through the narrow gap, lowering the pressure, and thus pulling the ship toward the bank. In reality the Bank Effect is not that well understood. Research is ongoing to better characterize how depth, distance, speed, propellor action, and other factors can affect the way a ship moves in a restricted waterway. We still have a lot to learn both in an academic sense and in nautical practice, a fact made very clear when this massive vessel found the edge of the Suez Canal.

Images of the first responder to the accident, a tiny excavator removing soil from the Ever Given’s gigantic hull, circulated around the internet like wildfire. The yawning gap between the machine’s assignment and its capability was just too ripe for parody - you could hardly check a single social media feed without being overwhelmed by the memes. In a long period of collective unrest and despondency during a global pandemic and the seemingly constant uncertainty surrounding who or what to believe about so many complicated issues, here was a story that anyone could understand: A boat was stuck in a canal. It was in the way of other boats that needed to get through. Simple as that. So why did it take so long to dislodge?

Humanity has a long and storied history of driving stuff into the ground so it will stay put, from the small (like tent stakes) to the massive (like the earth anchors used to hold guy wires for antenna masts). It’s pretty intuitive how this works. The pullout force is resisted by the friction between the soil and anchor. This ability to resist pullout is a function of the pressure against the soil and the surface area of the anchor. And when your anchor is a ship the size of a skyscraper, you obviously have both of those in abundance. It’s really no wonder that salvage crews struggled to unstick the Ever Given. But, there is a geotechnical phenomenon that I suspect made things even worse. And just a warning that I’m straying a little into speculation here, since the geotechnical details of the extraction have not been widely reported.

Soils with large grains, like sand, have an interesting property called dilatancy. Essentially, when they’re deformed, they expand in volume. If you’ve ever walked on the beach, this is probably something you’ve seen before. The water disappears from the surface because it soaks into the extra space created when the sand was deformed. This dilation occurs because the grains of sand, which were interlocked, rotate and lever against each other, pressing outwards as they do. This would not be a major issue except for one detail about the Ever Given’s hull: the bulbous bow, a feature included on many large ships to reduce drag. The hydrodynamics of bulbous bows are definitely worth discussing in a future video, but here is why it was such a problem for the Ever Given. Unlike if only the triangular hull was wedged in the sand, the bulbous bow was surrounded by soil on all sides. Essentially, the Ever Given put its appendage into a gigantic finger trap toy. Any movement of the ship would dilate the sand, effectively clamping down harder on the bulbous bow.

Ultimately it was impossible to simply pull the ship out. Removal took a much more extensive operation of dredging the sand from around the hull and lightening the ship by releasing ballast water, both to relieve the friction from the soil. Even the moon joined in on the operation, raising the tide in the canal to give a little more buoyancy to the foundered ship. After six days aground, the Ever Given was finally dislodged and traffic through the canal could resume. At the time, there were about 400 vessels waiting to make their pass and many more that had already diverted around the Cape of Good Hope. With a capacity of only around 90 ships per day, the backlog took about a week to clear up. That doesn’t mean the problem is resolved though. A weeklong disruption in such a big portion of global shipping traffic doesn’t untangle itself so quickly. The investigation into the exact cause of the incident is ongoing, and I’m sure many insurance claims are as well. In the meantime, I hope this helps you understand a few of the engineering challenges associated with navigating massive ships through tiny canals and what can happen when they run aground. Thank you, and let me know what you think!