Clair O. Haugen write:> I have information on a Norwegian sailing ship built in 1834, rated as 384 > commercial lasts, which I take to be a Norwegian measure. Does someone know > how to convert commercial lasts to English tons?
The answer to this question is simple if we limit ourselves to one country, one period of time and one type of cargo. It becomes much more difficult if we want to convert to another unit of measurement of another time and another country. We must also take into to account the different ways used to measure ships. This has not been standardised until modern times (or are there still local variations?).
According to the historical summary in Platou's treatise on Norwegian maritime law, before 1845 the burthen of a Norwegian ship was measured in "kommercelæst/er" of 5200 skaalpund or 2600 kg. This is a simplification, although I have not had time to check it, I do not believe the Norwegian skaalpund was equal to 0,5 kg. It was more likely close to the Swedish skålpund of 425 g.
With the new laws of the 7th of June 1845 a change to measurement of volume in units of "nya kommercelæster" took place. The new commerce last was set to be 165 Norwegian cubic feet.
In this case it might be interesting to see what Blunt (1837) has to say about the Norwegian measurements. At Bergen the commercial weights are:
21 barrels equal 10 1/4 quarters English. 1 barrel of tar equals 320 pots.
In a ship's cargo the last of Spanish and French salt, and the last of coal, contains 18 toender or barrels, and the barrel of 176 pots. 7 vog of stockfish are reconed as a last, and 120 barrels of tar to the keel.
References:
Oscar Platou: Forelæsningar over norsk søret.
Christiania, 1900.
Joseph Blunt: The Shipmaster's Assistant and Commercial Digest:
Containing Information useful to Merchants, Owners, and Masters of
Ships.
New York, 1837. 8vo, (2), xiii, 672 pp.
Since I was the one who was guilty of referring to Carpenter's Measurement (CM) when giving the tonnage figures for the Guy Mannering I will try to explain the differences between the various methods of measure tonnage at the time.
The Carpenter's Measurement was an unofficial measurement of cargo capacity which was popular in the earlier period. This simple formula intended to give an estimate of the cubic contents of a ship.
CM = (L×B×D) / 95
L = length of keel
B = breadth of beam
D = depth of hold
For double decked vessels D is considered equal to half the breadth.
The CM normally resulted in more inflated figures than the Old Custom House method. W.H. Webb, the builder of the ship Guy Mannering, always gave the size of his ships in round figures of CM.
The US (Old) Custom House Measurement, which was in use in the United States until 1865, was an adoption of the English Builder's (Old) Measurement where the length correction had been made smaller and the divisor larger to more accurately measure American ships. This system tended however to underestimate the cargo capacity for all but the sharpest vessels.
Old CHM = ((L - 3/5×B)×B×1/2×B) / 95
L = the length from the fore part of the stem to the after part of the stern-post, measured on the upper deck (on the middle deck of three-deck vessels).
B = the breadth from outside to outside of planking at the broadest part of the vessel.
D = the depth of hold from the plank of the deck to the ceiling of the hold (assumed to be 1/2 B). For single-decked vessels the actual depth was taken, instead of considering one-half as the depth.
The New Customs House Measurement system, which was based on the British system devised by Moorsom, was introduced in the United States in 1865. This system which used Simpson's rule to compute the volume of the the ship is still, with changes, the basis for the calculation of the gross tonnage.
If we study the different tonnage measurements for a couple of packet ships built by W.H. Webb we find that he tended to give fairly round figures for the CM.
Old New
Year CHM CHM CM Builder
1830 "Hibernia" 551 601 664 Brown & Bell
1845 "Havre" 870 928 1000 W.H. Webb
1847 "Yorktown" 1150 1341 1300 W.H. Webb
1849 "Albert Gallatin" 1435 1533 2000 W.H. Webb
1850 "Isaac Webb" 1359 1497 2000 W.H. Webb
1800
1860 "Alexander Marshall" 1232 1507 1450 W.H. Webb
1177
These figures are based on American formulas for tonnage measurement. Great Britain used slightly different formulas and also changed from the Old to the New method eleven years before the United States. Other countries not only used variations of these formulas or completely different ways to compute the tonnage, but also used units of measurement of length which were different.
I have tried to verify a couple of the measurements using the correct formulas but cannot get the same results as the official figures. It does not help to use the "Tables giving the length, breadth and tonnage of 3048 double decked vessels, of 206 to 2682 tons", computed by George Raynes, Esq., Shipbuilder, Portsmouth, NH, and published in The Merchant's and Mechanic's Assistant by I.R. Butts in 1858. It was my understanding that the published register length and breadth were the same values as used for the calculation of the tonnage.
You may have overlooked my note on "Carpenter's Measurement" from Saturday, October 14, where I also gave the official formula used to calculate tonnage in the United States up to 1865, ie during the period of interest.
!T = .022×(L^2.084)
Since tonnage basically is a measurement of volume, you should have a cubic exponent. This also follows from the fact that you would find strong correlations between both length and breadth and between breadth and depth.
Updated 1996-07-06 by Lars Bruzelius
Sjöhistoriska Samfundet | The Maritime History Virtual Archives | Tonnage.
Copyright © 1996 Lars Bruzelius.