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 have
two demonstrations to help us understand.
I’m Grady and this is Practical
Engineering. In today’s episode,
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. Luckily I have an acrylic flume
in my garage, and I can try to demonstrate how
this works. But 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). This is a cross-sectional view
of the Suez Canal and the Ever Given to scale. 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.
Let me show you what I mean.
My flume isn’t long enough to simulate a boat
moving through a canal, but if you switch your
frame of reference to that of a ship, it can
simulate the movement of water passing by.
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. I’m using some brick pavers as
my surrogate shipping vessel. Watch what
happens when I drop them in the flow.
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. Obviously,
this demo is exaggerated from a real situation,
but 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. It seems pretty straightforward
when you exaggerate it in a demo like this,
but 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. Watch what happens when I strike the
top of this sand in my beaker. Notice how the
sheen of water on the surface disappeared?
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 video 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 for
watching, and let me know what you think!