Dictionary Definition
burthen n : a variant of `burden' v : weight down
with a load [syn: burden,
weight, weight down]
[ant: unburden]
User Contributed Dictionary
English
Pronunciation

 Rhymes: ɜː(r)ðən
Noun
 the tonnage of a ship based on the number of tuns of wine that she could carry in her holds.
 an archaic variant of burden.
Quotations
* 1883: Robert Louis Stevenson, Treasure Island
 The other men were variously burthened; some carrying picks and shovels  for that had been the very first necessary they brought ashore from the Hispaniola  others laden with pork, bread, and brandy for the midday meal.*1798, William Wordsworth, Lines composed a few miles above Tintern Abbey, lines 3643 (for syntax)
 Nor less, I trust,
 To them I may have owed another gift,
 Of aspect more sublime; that blessed mood,
 In which the burthen of the mystery,
 In which the heavy and the weary weight
 Of all this unintelligible world,
 Is lightened:
 1817: Jane Austen,
''Persuasion
 It was with a daughter of Mr Shepherd, who had returned, after an unprosperous marriage, to her father's house, with the additional burthen of two children.
Extensive Definition
Builder's Old Measurement (BOM) is the method of
calculating the size or cargo capacity of a ship used in England from
approximately 1720 to 1849. The BOM estimated the tonnage of a ship based on
length and maximum beam. The
formula is:
= \frac where:
 Length is the length, in feet, from the stem to the sternpost;
 Beam is the maximum beam, in feet.
Thus, BOM estimates the weight of the cargo
carrying capacity of a ship measured in tons, a weight that is also
termed deadweight.
The Builder's Old Measurement formula remained in effect until the
advent of steam propulsion. Steamships required a different method
of measuring tonnage, because the ratio of length to beam was
larger and a significant volume of internal space was used for
boilers and machinery. In 1849 the Moorsom
System was created in Great
Britain. Instead of calculating deadweight, the Moorsom system
calculates the cargo carrying capacity in cubic feet, a volumetric
measurement rather than a weight measurement. The capacity in cubic
feet is then divided by 100 cubic feet of capacity per gross ton,
resulting in a tonnage expressed in tons.
History and Derivation
The first tax on the hire of ships in England was
levied by King Edward
I in 1303 based on tons of burthen (burden). Later, King
Edward
III levied a tax of 3 shillings on each "tun" of imported wine.
At that time a "tun" was a wine container of 252 gallons weighing
about 2240 lbs. In order to estimate the capacity of a ship for tax
purposes, an early formula used in England was
= \frac
where:
Or by solving : = \frac
In 1694 a new British law required that tonnage
for tax purposes be calculated according to a similar
formula:
= \frac
This formula remained in effect in until the
Builders Old Measurement rule was put into use in 1720, and then by
Parliamentary law in 1773.