Builder's Old Measurement  From Wikipedia, the free encyclopedia
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also: tonnage  Builder's Old Measurement (BOM or bm) is the
method used in England from approximately 1650 to 1849 for
calculating the cargo capacity of a ship. It is a volumetric
measurement of cubic capacity. It estimated the tonnage of a
ship based on length and maximum beam. It is expressed in "tons
burden" (Early Modern English: burthen, Middle English: byrthen
), and abbreviated "tons bm".  The formula is:  {{Tonnage}} =
\frac {({Length}- ({{Beam}\times\frac{3} {5}})) \times {Beam}
\times \frac {Beam}{2}} {94}   The Builder's Old Measurement
formula remained in effect until the advent of steam propulsion.
Steamships required a different method of estimating 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. The
Moorsom system calculates the