Colonial Tonnage Measurement: Five Philadelphia Merchant Ships as a Sample

Economic historians have been aware for some time of the questionable nature of some of the tonnage figures given for the ships of the English colonies in the Western Hemisphere in the eighteenth century. Several authors who have written on colonial shipbuilding or colonial trade have noted the authoritative declaration of Thomas Irving which was laid before the House of Commons in 1792 and have tried to take his evidence into account in their own investigations. Irving, who from 1767 to 1774 had held the dual position of Inspector General of Imports and Exports and Register of Shipping in North America, stated that while he was in office North American vessels had been consistently registered at two-thirds of their real tonnage. He urged that this deduction be repaired and real tonnage re-established before any attempt be made to compare statistics from that time with those of a later period. Other scholars have either chosen not to notice Irving's claim or have discounted it as of moot significance. Such ambivalence is understandable, for Irving's assertion is narrowly based, confused, and misleading. Still, the sweeping scope of his charge and the even broader testimony of some of his contemporaries who have both agreed with him and expanded upon him have combined to leave the precise nature of all colonial tonnage figures in serious doubt. Given the renewed interest in tonnage measure and the growing trend toward the use of compiled tonnage statistics as a rough and ready measure of trade, it becomes important to resolve this doubt.