Today, what is a T-U-N? The University of Houston's College of Engineering
presents this series about the machines that make our civilization
run, and the people whose ingenuity created them.
My Classic Comics version of Moby Dick came
out in 1942 and it cost me a dime. Comics were then forbidden fruit -- Batman
or a classic -- it hardly mattered. That Moby Dick now sells for
thousands of dollars. And one frame of its story sticks in my mind. A sailor,
flensing a freshly caught
whale, cries, "Into the tun you go." What in the world was a tun, spelled T-U-N?
I went off puzzled.
Well, it's a very big barrel. To be precise, it's one that holds 252 gallons
-- equal to six oil barrels. But tun was also used loosely. The
Heidelberg Tun is a
huge wine barrel in the cellar of Heidelberg castle. It holds 58,000 gallons.
The word tun echoes in our language as the T-O-N, ton -- no longer a
unit of volume, but of weight. That's because it took 2100 pounds of water to
fill an old tun. Our T-O-N ton is five percent less than that, and a metric
T-O-N-N-E is five percent more.
Since I've mentioned Moby Dick, let's follow the tun back to ships.
A ship's size can be reported either in length, or in one of several measures
that take volume and weight to be interchangeable.
The historic measure of ship size was the number of T-U-N tuns for which it
could be taxed. It was a crude measure of volume. Now a ship's tonnage is
calculated by a variety of different formulas, none of which tell the true
weight of the ship. Terms like gross register tonnage, net tonnage
and more are all rough indications of a ship's volume, calculated in different
ways. They still echo the old T-U-N tun.
So, how do we know how big a ship really is? Well, for that, we look at
lightweight and deadweight tonnage. Lightweight is the actual
weight of the vessel when it's completely unloaded. Deadweight tonnage is the
weight of everything the ship carries -- cargo, fuel, passengers, stores ...
The largest ships ever built were supertankers. Today, all the existing
single-hull supertankers have been scrapped or converted. While they carried
oil, their deadweight tonnage ran to a half million tons. A new generation
of double-hulled tankers is now poised to replace them. But, at this writing,
container ships are the largest in service. They reach 150,000 deadweight tons.
And, close on their heels, are big cruise ships.
The Batillus supertanker: 1976-1985: Once the world's largest ship as
measured by deadweight tonnage (555,000 tonnes).
Behind all this is the strange way we mix up weight and volume. That's because
we live and die by water. (Never mind that water in the ocean weighs three
percent more than fresh water.) Think about the quart -- a volume of thirty-two
fluid ounces. But a fluid ounce is the volume of an ounce of fresh water.
We once lived in world where weight and volume flowed together, and a world
where a few percent didn't much matter. That was the world where a big barrel
might be a T-U-N or a T-O-N -- an old world, where everything seemed to come
back to an amount of water.
I'm John Lienhard at the University of Houston,
where we're interested in the way inventive minds
Please see the Wikipedia pages on the various terms introduced here.
See especially those for
See also Episode 2126. Barrel diagram is
signage for the Mayflower exhibit in Plymouth, MA. Thanks to Wikimedia
Commons for the Batillus photo.
For more on Batillus class ships see Episode 2839.
The Engines of Our Ingenuity is
Copyright © 1988-2011 by John H. Lienhard.