Demystifying Measurements - Or, Which Ton Are You Talking About?
In a past blog, I have discussed the background behind common phrases which originated in the maritime industry. For your enjoyment, this blog will discuss various measurement terms, where some have originated from, and what the use of some more arcane measurements you may (or, hopefully, may never) come across. And just so my dear readers understand, it is not only laypersons who struggle with these measurement terms – we engineers find the variety and overlapping instances confusing and frustrating!
Mass, Weight, and Volume
Naturally, there is a relationship between mass and volume – the density of a liquid or solid multiplied by its volume gives the mass of an object. So, by logical extension, a ton of water should equal a ton of mass. Unfortunately…no. A ‘ton of water’ is a volume equal to exactly 56 ‘Buckets’ or 224 ‘Gallons’ in the United Kingdom (UK) – but only about 53.8 ‘Buckets’ in the United States (US). And the difference between a ‘Bucket’ in the US versus the UK? 25.1 US fluid ounces, or ½ fluid ounce less than a ‘Fifth’. So, in the US ‘Bucket’, you get a UK ‘Bucket’ plus an extra bottle of rum. Confused yet? Good.
Volume measurements started as a way to standardize trade – when merchants brought a ‘Bucket’ of goods to the market, people needed to know if they were getting the same amount of goods from ‘Paul’ and ‘Peter,’ because each had their own bucket. The terms ‘Bucket,’ ‘Bushel,’ ‘Barrel,’ ‘Butt,’ and ‘Tun ’ are all volumes related to physical containers. The term ‘Ton,’ which eventually referred to weight, comes from the term ‘Tun,’ the largest wine cask, and became synonymous with any very large weight. For ships and freight, ‘Ton’ still refers to the volume of carriage, not the weight – equal to 100 cubic feet on a ship (the ‘Register Ton’), but only 40 cubic feet of freight. So, you can put 2-1/2 tons of freight in a Register Ton of a ship. For weights, we’ve determined a ‘Ton’ is a large weight – how large? Well, it was first standardized at 20 hundredweight – nominally 20 times 100 pounds (100 ‘weight’). However, there were ‘Short’ hundredweights (100 pounds) and ‘Long’ hundredweights (112 pounds). These became the ‘Short Ton’ (2000 pounds) and the ‘Long Ton’ (2240 pounds) – ‘Short Tons’ are used to certify the capacity of cranes; ‘Long Tons’ are used to classify the weight of cargo. Except in Europe and Asia – they use the ‘Metric Ton’ (or ‘Tonne,’ 1000 kilograms or 2204 pounds).
Distances and Areas
The measurement of distance is similar to the measurement of volume – mankind has need for a common reference to the dimension of an object. Measurements such as the ‘Foot,’ ‘Hand,’ ‘Pace,’ ‘Span,’ ‘Rod,’ and ‘Cable’ all refer to common things we could relate to and measure from; most people have a hand or foot they can put beside something and get a relative sense of its size. Because people aren’t all the same size, these common things could only give relative measurements; King Edward II (of the UK) defined the quantity of an ‘Inch’ as 3 grains of dry, round barley end-to-end lengthwise. From there, the ‘Foot’ was defined as 12 inches, the ‘Hand’ as 4 inches, the ‘Span’ as 9 inches, and a ‘Pace’ as 30 inches.
Land Surveyors came up with their own set of measurements – ‘Link,’ ‘Pole,’ ‘Chain,’ and ‘Furlong.’ A ‘Chain‘ is 66 feet, and there are 100 ‘Links’ in a ‘Chain’ or 4 ‘Rods.’ 10 ‘Chains’ equal one ‘Furlong.’ The derivation of these terms is pretty simple – chains are made of links, and rods are used to hold up the target for the Land Surveyor to sight. 10 square ‘Chains’ equals one ‘Acre’ and there are 640 ‘Acres’ in one ‘Section’ of land – 1 square mile. There are also 4 ‘Homesteads’ in that ‘Section,’ and 144 (1 gross) of ‘Homesteads’ makes a ‘Township.’ Note, not all building references are by Land Surveyors – there are 1 billion (1,000,000,000) ‘Barns’ in a square Nanometer, courtesy of theoretical Physicists (“Can’t hit the broad side of a ‘Barn’” with your particle)
Oh, and you ‘Star Wars’ fans – a ‘Parsec’ is defined as the distance perpendicular to the orbit of the Earth equal to the intersection of a one arc-second angle (about 3.086 x 1013 kilometers).
Pressure and Stress
Maybe not so ironically, pressure and stress use the same units – I’m sure all of you feel stress when under pressure. Now you know why – they’re the same quantity! This is one of Engineering’s greatest nightmares – what unit is which? Since pressure is force per unit area – or force per distance squared – we got ‘pounds per square inch,’ ‘tons per square foot,’ ‘newtons per square millimeter,’ or any other combination of force and distance you wish. There is also ‘Pascals,’ ‘Bar,’ ‘Atmospheres,’ and ‘Torr’ as well as ‘Inches of Water,’ and ‘Millimeters of Mercury.’ The latter are derived from the devices we measure pressure with – manometers (‘mano’ is from Greek, manós, ‘thin, rare, sparse’ and métron [also Greek], ‘measure’). Simple manometers are U-shaped tubes filled with a liquid that reacts to the difference in pressure by having a difference in height – common liquids are water (for low-pressure differences) and mercury (for high-pressure differences).
The unit ‘Pascal’ is defined as the pressure of 1 Newton acting on 1 square meter. Since 1 Newton is about 1/10 of a kilogram or about 1/5 of a pound and a square meter is about the footprint of an easy chair, this is not a lot of pressure. A ‘Bar’ is defined as 100 kiloPascals (100,000 Pascals), which is slightly below the average atmospheric pressure at sea level on Earth. It is a useful term when quantifying the pressure in terms of standard atmospheric pressure. ‘MilliBars’ (one-thousandth of a Bar) is a standard measurement for atmospheric pressure and is useful in determining storm patterns. An ‘Atmosphere’ was another attempt to relate sea-level atmospheric pressure to a single number; one ‘Atmosphere’ has been defined as 101,325 Pascals or roughly 14.7 pounds per square inch. One ‘Atmosphere’ is also the most negative pressure which can be exerted on Earth – absolute vacuum. The ‘Torr’ is a rarely used unit which is defined as 1/760th of a standard ‘Atmosphere;’ it was originally supposed to be equal to 1 millimeter of mercury, but changes in the metric system standards changed the result.
Oh, and the volume of a ‘Fifth?’ If you guessed that a ‘Fifth’ of liquid (such as rum) is equal to 1/5 of a ‘Gallon,’ give yourself an A+ for understanding this blog!
About the Author
Steven M. Lindholm, P.E., P.M.P., NAMS-CMS is a consulting engineer with our Oakland, CA office.
Mr. Lindholm provides consulting on inspection, evaluation, and design analysis of ship construction; stability; propulsion and auxiliaries condition assessment; ballast water treatment systems; vibrational analyses; and ship motion. He interprets and applies international (International Maritime Organization (IMO), class society, and flag state), United States Coast Guard (USCG/CFR), and regional regulations/guidelines to maritime casualties. Mr. Lindholm explores root cause investigation and analysis of mechanical damage to equipment, components, and materials, including fracture analysis and failure analysis, and prepares repair and replace cost estimates for marine, industrial, commercial, and residential systems.
You may contact either Steve at firstname.lastname@example.org for your forensic engineering needs or (925) 674-8010
Learn about how EDT Forensic Engineering & Consulting approaches cause of damage, and forensic engineering by assigning a file today.
1 The Nautical Origins of Common Phrases, October 17, 2019, www.edtengineers.com
2 Another definition of ‘tun’ can be found in the blog A “Tun” of Fun, August 8, 2019, www.edtengineers.com, regarding beer-making