What’s Up: Lunar Tides and the Suez Canal

by | Apr 5, 2021 | Uncategorized | 0 comments

IMAGE: Russian satellite “Canopus B” image showing the megaship Ever Given stuck in the Suez Canal. CREDIT: Roscosmos

Our What’s Up segment is about astronomy, just in a roundabout way.

Earlier this week a large container ship ran aground in the Suez Canal, where it is currently still blocking [Ed. note: Not anymore!] all maritime traffic through one of the busiest waterways in the world. The vessel, named the Ever Given, measures 400 meters long and 59 meters wide, making it one of the largest container ships in the world and challenging to navigate through the relatively narrow Suez Canal.

In an image from the Russian satellite Canopus-B, you can get a sense of just how stuck this ship is, and a hint at its size, which is essentially the size of the Empire State Building laid on its side!

Navigation in the Suez was made even more challenging for the Ever Given by a sandstorm and 50-kilometer winds, which caused the ship to lose control and hit the bottom of the canal. Satellite images show the Ever Given sitting diagonally across the entire width of the canal. Reports say it’s going to take days, maybe even weeks, to refloat the ship and allow traffic to resume.

IMAGE: Tide measurements for the Suez Canal. CREDIT: https://www.tide-forecast.com/locations/Suez-Egypt/tides/latest

According to a 2019 paper published in the Journal of Marine Science and Engineering, terminals and waterways are struggling to accommodate so-called mega container ships like the Ever Given. Due to safety concerns, vessels longer than 400 meters need permission from the Suez Canal Authority to transit the canal, putting the Ever Given right at the max length. Likewise, the ship’s beam and draft — that is, the breadth of the ship at its broadest point and the vertical distance between the waterline and keel — are barely within the maximum allowable through the canal. This means there is almost no room (literally and figuratively) for error. It also raises concerns about the safety of allowing larger and larger ships through the canal. The Ever Given is the fourth ship to run aground in the Suez since 2016.

We have to admit that we’re out of our depth when it comes to shipping, and Ally, who was a project manager for a global shipping company – and who is currently very glad she is now a producer for us and not involved in this particular nightmare – wrote the earlier portions of this story.

Now, what does this have to do with astronomy? The first thing I did when I heard about this grounding was pull up a tidal chart of the Suez Canal.

CREDIT: timeanddate.com

Over the course of the month, the timing of the tides, and the highs and lows of the high and low tides all vary with the phase of the Moon. Ideally, you want to put a boat like this through on the highest of high tides, which is not what they did. When the boat ran aground on Tuesday, the Moon was just past first quarter.

When the Moon and the Sun are at right angles in the sky, we see only half of the Moon illuminated, and the tides are just not as high or low because the Sun and Moon are pulling on the Earth at cross-purposes.

The next full Moon comes on Sunday, and it brings with it higher tides. The exact time of the highest tide actually lags a bit thanks to everything rotating, and my early fear was they’d need to wait for that higher high tide to get things moving again.

In a new article appearing in Bloomberg, Lucia KAssai and Robert Tuttle report that it’s now official: that Monday tide is being seen as the best bet to get this boat free.

CREDIT: timeanddate.com

Each day, we experience two high tides: one when the Moon is almost but not actually straight overhead, and one when the Moon is almost straight beneath our feet. That is because planetary rotation carries the tide ahead of the Moon.

Low tides come just before moonrise and just before moonset.  If you’re ever at the beach you can now surprise your friends by looking at the Moon and knowing the tide, at least if the moon is in the sky. But hey, this gives you one chance a day, most days, to show off your astronomy knowledge.

More Information

Large container vessel Ever Given blocks Suez Canal (Ship Technology)

Tendency toward Mega Containerships and the Constraints of Container Terminals,” Nam Kyu Park and Sang Cheol Suh, 2019 May 6, Journal of Marine Science and Engineering

Suez Canal blockage: how cargo ships like Ever Given became so huge, and why they’re causing problems (The Conversation)

Here’s how the full moon helped free the stuck ship Ever Given in the Suez Canal (Space.com)

What Causes Tides? (timeanddate.com)

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