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Noah's Ark by Edward Hicks, 1846. (Image: Wikimedia Commons/Philadelphia Museum of Art)

Could Noah’s Ark Float? In Theory, Yes

Basic physics suggests that an ark carrying lots of animal cargo could float, but science doesn’t support other facets of the biblical tale

smithsonian.com

Noah has a lot going for him, in the biblical tale and in the recent Hollywood adaptation. Divine help would be a pretty useful tool in a quest to round up two of every species on the planet and build a gigantic ark to survive an apocalyptic flood. But, is the story rooted in truth or is it merely fable?

Scholars and passionate internet commenters have long debated that question. There are quite a few holes in Noah’s story. Geological evidence of epic flooding exists, but tying it to mythical flood stories is tricky. It doesn't help that archaeologists have made multiple false claims of discovering the ark on top of mountains across the Middle East.

However, the Bible is clear on one thing: Noah got specific instructions for the ark’s dimensions (300 cubits long, 50 cubits wide and 30 cubits high) and material (“gopher wood”). Gopher wood may refer to pine, cedar, or cypress wood.

So, if one could hypothetically build an ark to the specifications outlined in the Bible, and actually cram two of every species on the boat, would it float or would Noah have found himself in a Titanic-like scenario? That’s what four physics graduate students at the University of Leicester wondered. As part of a special course that encourages the students to apply basic physics principles to more general questions, the team did the math and found that an ark full of animals in those dimensions could theoretically float. They recently published their research in a peer-reviewed, student-run publication, the Journal of Physics Special Topics.

“You don’t think of the Bible necessarily as a scientifically accurate source of information, so I guess we were quite surprised when we discovered it would work,” said Thomas Morris, one of the students who worked on the project, in a statement.

To float, a boat has to exert the same amount of force on the ocean as the weight of the water it displaces. This buoyancy force is essentially the biggest weight the ark could hold and not sink. To put it another way, an object with a density greater than water will sink. So if the Bible gives an approximate volume of the ark, and after factoring in the mass of the wood used to build it, one could figure out how much mass the system could take before it becomes more dense than water and sinks.

Now that we've defined the constraints on the system...what in the world is a cubit? Ancients defined a cubit as the distance from a person's elbow to tip of their middle finger. In modern units, this can typically range from 45.5 centimeters to 52.3 centimeters.

In their study, students decided on an average length for their calculations: 48.2 centimeters. This means that, by their approximations, the ark would have been 144.6 meters long, 24.1 meters wide, and 14.46 meters tall—the size of a very small cargo ship. They went with cypress wood, though pine and cedar wood have similar densities. Using the density of cypress, they calculated the weight of this hypothetical ark: 1,200,000 kilograms (by comparison the Titanic weighed about 53,000,000 kilograms). Based on the density of sea water, they figured out that an empty box-shaped ark would float with it's hull only dipping 0.34 meters into the water.

But what about an ark filled with human and animal cargo? Working backwards they assumed that the maximum weight would put the waterline right just below the top of the ark—if the ark is immersed beyond it's full height, water would spill into the vessel and the ark would capsize.

Forcing the bulk of the ark down into the water while still keeping it afloat would displace about 20 Olympic-sized swimming pools worth of sea water. Knowing the volume of displaced sea water, and knowing that an object in water displaces its own weight, they crunched the numbers and found the total mass needed to displace that water. They subtracted the mass of an empty ark and found that the ark could hold 50,540,000 kg. For some perspective: the average sheep is about 23.47 kilograms, so the biblical boat could have held about 2.15 million sheep.

Fitting two of each of all the world's animals in the ark is an entirely different matter, and scientists question how many species Noah would have needed to save to produce the modern populations of species that inhabit our planet today. Scientists have characterized about 1.7 million species to date, so the students argue that, if the average mass of species represented on the ark was the average mass of sheep, the ark would theoretically have been able to accommodate them all without capsizing. However, some estimates put the total number of discovered and undiscovered species on Earth closer to 8.7 million, which would make for a lot of wet proxy sheep.

Could Noah's ark really have handled 8.7 million species? It seems unlikely, but biblical scholars and creationists have a workaround, arguing that the number of animals needed on the ark could be reduced to "kinds" instead of species and then suggesting that God introduced the possibility of endless hereditary variety into the genetic material of passengers and animals on the ark. Their estimates put Noah's cargo from around 2,000 to 50,000 animals. Marine life, of course, could stay in the ocean—two blue whales on deck would not only die but capsize any ship.

Even if one could fit all the needed animals on the boat, and if those animals could survive the cramped cruise (the study made no estimates regarding the weight of the food or freshwater needed to sustain the ark population), building a seaworthy vessel is another factor.

A boat sunk to its max in the water while still staying afloat could easily take on water from any breaching waves. And according to Euler-Bernoulli beam theory, the strength of a wooden beam decreases with its size, so because when things get bigger they break more easily, the beams that held this huge ark together might have been extremely fragile. Else the beams were short, which would also introduce structural weaknesses due to the higher number of seams between wood planks.

The students are quite clear about the fact that their study does not settle debate over the veracity of Noah’s story. “We’re not proving that it’s true, but the concept would definitely work,” said Morris.

Regardless, given the growing threat of climate change, it’s comforting to know that that should rising sea levels engulf coastal cities, 2.15 million sheep can, in theory, float on a cypress wood ark the size of a small cargo ship.

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About Helen Thompson
Helen Thompson

Helen Thompson writes about science and culture for Smithsonian. She's previously written for NPR, National Geographic News, Nature and others.

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