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Eighteenth-Century Shipping Tonnage Measurements

Published online by Cambridge University Press:  11 May 2010

Christopher J. French
Christopher J. French
Affiliation:
Kingston Polytechnic
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Extract

During the eighteenth century various methods existed for obtaining shipping tonnages; Most official records of shipping throughout this period record a vessel's “registered tonnage” which was the figure which appeared in the vessel's certificate of registration. This registered tonnage was less than a vessel's “measured tonnage.” The latter was the basis for building, buying, and selling vessels and was computed by means of a given formula. Registered tonnage was then estimated at roughly two thirds of measured tonnage and the figure rounded down to the nearest large whole number. This practice was encouraged by ships' captains and ship owners who wanted to minimize lighthouse and port duties that were based on tonnages. Thus only when the registration of measured tonnages became compulsory did shipping tonnages in the records become reasonably accurate.

Type
Notes
Information
The Journal of Economic History , Volume 33 , Issue 2 , June 1973 , pp. 434 - 443
Copyright
Copyright © The Economic History Association 1973

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References

I would like to thank the following who read earlier drafts of this paper and made useful suggestions and criticisms: Professor W. E. Minchinton, Dr. H. E. S. Fisher, J. Stanyer, N. F. R. Crafts, and Professor G. M. Walton. I would particularly like to thank Dr. J. J. McCusker for his assistance.

1 Usually a multiple of five. See Lyman,, John“Register Tonnage and its Measurement,” American Neptune, V (1945), pp. 223–225.Google Scholar In fact the position was more complicated than this simple statement implies, for during the eighteenth century there were effectively three tonnages for each vessel: her measured tonnage, her registered tonnage, and her “tons burden,” the latter being defined as “the number of tons weight which would lade a ship previously empty down to her minimum safe freeboard or loadline.” Davis,, RalphThe Rise of the English Shipping Industry in the Seventeenth and Eighteenth Centuries (London: Macmillan, 1962, reprinted Newton Abbot: David &Charles, 1972), p. 178.Google Scholar Davis points out that by the end of the eighteenth century tons burden was actually greater than measured tonnage (Shipping Industry, p. 74). Here we are concerned with the difference between registered (the tonnage actually attributed to a vessel in its register) and measured (the tonnage of the same vessel calculated by means of a given formula) tonnage. For the background of the evolution of the English registered tonnage see Lane,, Frederic C.‘Tonnages, Medieval and Modem,” Economic History Review, 2nd series, XVII (Dec. 1964), pp. 215–7Google Scholar, 228–9. For greater detail see also the five articles by Salisbury, William in Mariner's Mirror, 1966–1968.Google Scholar

2 6 &7 W.“M. c.12.IX.

4 26 Geo. III, c.60. For various aspects of this Act see Jarvis,, Rupert C. “Eighteenth-century London Shipping,” in Hollaender, A. E. J. and Kellaway, W. (eds.), Studies in London History (London: Hodder &Stoughton, 1969), 403–425Google Scholar, and W. Salisbury, “Early Tonnage Measurement,” pp. 334–336.

5 Jarvis, Ibid., p. 413.

6 McCusker,, John J.“Colonial Tonnage Measurement: Five Philadelphia Merchant Ships as a Sample,” Journal of Economic History, XXVII (Mar. 1967), 82–91.CrossRefGoogle Scholar

7 Walton,, Gary M.“Colonial Tonnage Measurements: a Comment,” Journal of Economic History, XXVII (Sept. 1967), 392–397.CrossRefGoogle Scholar

8 Cited by McCusker, “Colonial Tonnage Measurement,” p. 82.

9 This also applied to English vessels, not only colonial ones. Writing of English tonnage measurements for 1760, Macpherson claimed that “the real tunnage may in general be reckoned full fifty per cent above the reputed.” See Macpherson,, DavidAnnals of Commerce (London, 1805), vol. III, p. 340.Google Scholar

10 McCusker, “Colonial Tonnage Measurement,” p. 90.

11 Walton, “Colonial Tonnage Measurements,” pp. 394–396.

12 Ibid., p. 393.

13 Ibid., p. 397.

14 These lists are all to be found in the PRO: for Jamaica under C.O.142/20–22; for Grenada under C.O.106/2–4; and for Antigua under C.O.10/2. In the case of Jamaica, the last quarter of 1786 has also been included.

15 This is the only information available in the Antigua lists.

In this case, the regression curve equation is y = 140.7 + 0.7x, where y = measured tonnage, and x = registered tonnage.

17 See below.

18 This is smaller than the estimate given by Thomas Irving in his report to William Pitt, 12th December, 1791 (PRO Customs 17/12, f.1). This report estimates measured tonnage at fifty percent greater than registered tonnage, but from the text of the report it is clear that Irving had not taken into account the change in measuring tonnage of 1773. It is possible that Irving was referring to estimates he made before 1773. McCusker also discusses this point when examining a similar report made by Irving. See McCusker, “Colonial Tonnage Measurement,” pp. 82–86.

19 By correlating the measured and registered tonnages in different tonnage ranges, the following results were obtained:

20 There were regional variations according to Salisbury. See his “Early Tonnage Measurement in England. Part IV. Rules used by Shipwrights and Merchants,” Mariner's Mirror, LIII (Aug. 1967), pp. 258–260.Google Scholar

21 There are not enough vessels in the sample to examine ships from individual ports. By correlating the measured and registered tonnages of London registered and then Outport registered vessels, the following coefficients were obtained: London 0.72***; Outport 0.78***.

22 The formula for obtaining measured tonnage certainly did not vary from port to port after 1786. See Salisbury, “Early Tonnage Measurements,” p. 336.

23 The naval office shipping lists only distinguish between the very broad categories (“ship,” “snow,” “schooner,” etc.) and out of the present sample of 63 vessels, only 3 vessels were not described as ships. Besides, design and size were very closely related.

24 Salisbury, “Early Tonnage Measurement,” pp. 336–337, and Lane, “Tonnages, Medieval and Modern,” p. 229.

25 See above. Also, if only colonial vessels in Professor Walton's study are examined (21 in all), then the registered tonnage of colonial owned ships was 54.1 percent less than measured tonnage (based on the 1695 formula), or measured tonnage was 118.0 percent greater than registered.

26 McCusker's example covers the years 1740–1775, and Irving made his calculations in 1771. See McCusker, “Colonial Tonnage Measurement,” pp. 84–85 and 89.

27 It should be noted that there are some errors in Walton's figures. In his transcription of Virginia shipping lists Walton made twelve mistakes. Five registered tonnages were recorded wrongly, and seven measured tonnages. Also, several vessels were given incorrect names. However, these mistakes, when corrected, do not significantly alter Walton's conclusions. His corected tables should read as follows.

Table I: Registered Tonnage, 3522; Measured Tonnage, 5120; Difference, 1598; Ratio of Difference to Measured Tonnage, 0.312; Ratio of Difference to Registered Tonnage, 0.454. Table II: Registered Tonnage, 3078; Measured Tonnage, 5096; Difference, 2018; Ratio of Difference to Measured Tonnage, 0.396; Ratio of Difference to Registered Tonnage, 0.656.

These corrected figures indicate that in the example given by Walton registered tonnage was 35.4 percent less than measured tonnage, or measured tonnage was 54.8 percent greater than registered tonnage.