A POUND IS A POUND, BUT A TON IS A
MUCH MORE WEIGHTY MATTER: Measuring Cargo, Space, Is Complex
Panama Canal Review - April, 1964
A TON IS a ton is a ton. But not
always, It may be a tun or even a Panama Canal net ton.
Panama Canal employees, especially admeasurers and others connected with shipping, do business with all kinds of tons and even handle a tun or two now and then.
But to the average person, who is unfamiliar
with nautical or shipping tons, metric tons, gross, net displacement and deadweight
tonnage and of course, Panama Canal gross and net tonnage, will leave him all at sea.
In an article written some years ago, Elmer Stetler, former Chief Admeasurer in Balboa, said that the layman could be lost in a maze and figuratively buried under tons. Tonnage he said, just grew like Topsy and could not be explained logically. It was subject to the vagaries of countries, ship owners, merchants and tax laws.
From the historical standpoint, measurement of ships is only about 100 years old. Prior to 1854, only the crudest and loosely approximate methods were used. the formulation of the Panama Canal rules of measurement drawn up by Prof. Emory R. Johnson in 1912 he called the greatest milepost in measurement history.
The excellence of the system devised by Professor Johnson is demonstrated by the fact that the average ratio of the weight of the cargo carried in long tons through the Panama Canal is almost equal to the space tons or Panama Canal net tonnage of the vessels carrying this cargo.
The Johnson system was based mainly on determining the earning capacity of a vessel with 1 ton for each 100 cubic feet of enclosed revenue producing space. the system of calling 100 cubic feet a gross ton was devised by George Moorsom, an Englishman commissioned in 1854 by the British Board of Trade to devise rules to cover the measurement of ships scientifically.
During the middle ages the volume of ships was measured by a unit called a "ton" in some parts of Europe and by a "last" in others.
The word ton originally did not appear to have expressed weight. It was derived from the old English word "tun" which dates back to the Latin of early middle ages where the word "tunna" occurs, meaning barrel. And the barrel was used to carry wine.
According to Stetler, the transport of wine had a great influence on the origin of tonnage for in that trade only cargoes of one description of goods occurred. the weight per unit space of wine barrels required that a vessel have its entire hold filled with them in order to navigate safely.
In 1423 King Henry V of England decreed that wine should be in "tuns" of less than 252 gallons. Later, when trade expanded to the point that it became necessary to have an adequate measure of weight a vessel would lift as well as volume, a tun became a measure of weight of roughly 2,240 pounds.
The "last" was a measure of weight adapted especially for the carriage of corn in the north of Europe. Originally the weight which would be transported by a wagon drawn by four horses or on two carts drawn by two horses, it was often estimated at 4,000 pounds.
There was also the "keel" which originally was a flat bottomed boat used to transport coal on the River Tyne to Newcastle. It was decreed in 1422 that keels should have the portage of 20 "Chaldrons" corresponding to eight "waggons" with a capacity of 126 cubic feet. this is now equivalent to 21.2 long tons.
Then there is the displacement ton which has evolved as a unit approximately equal to the volume of a long ton weight of sea water or 35 cubic feet. and the measurement or freight ton, a unit of volume for cargo freight usually reckoned at 40 cubic feet.
These are only a few of the units of measurement used by commerce and shipping in the past and are still kept in use in modern times. The method by which ships are measured at the Panama Canal is as close an approximation to the actual net available cargo and passenger space as is possible to determine and was the first scientific exact system evolved that made the term "net tonnage" mean something, Stetler said.
But, he said, if past commercial growth compelled the retirement of such approximate standards of measure as "tuns of wine," "waggons of corn" etc., it is not too much to expect that refinements will be made in the future to the present tonnage laws which are the outgrowth of such crude units. they will become more exact and practical for the new type of ships now being developed for special purposes.
Presented by CZBrats
October 4, 1998