Page 37 - Nicolaes Witsen & Shipbuilding in the Dutch Golden Age

Figure 1.14. Van Yk’s illustration of a surveyor determining the shape of a vessel being measured.
The purely speculative nature of Witsen’s calculations becomes apparent when we c ompare his method w ith the actual methods used to estimate a ship’s burden in the seventeenth century. The main point of interest was the cargo capacity or, in the case of warships, the carrying ca- pacity in terms of ordnance, supplies, and crew . Nobody was in the leas t interested in superfl uous figures such as displacement or actual weight of a ship.
How then was the c arrying capacity determined? We know of three methods. The first and s implest one was purely empirical: an empty ship was loaded with cannon balls until it reached the load line. As the weight of the cannon balls was known (in pounds), one could easily de- duce the weight in lasts (lasten) by dividing by 4,000, as the seventeenth-century last was equivalent to about two tons.26 Both Witsen (p. 242) and Van Yk (p. 320) mention this simple but labor-intensive method. As a result, its chief drawback was that, rather than measuring each ship separately, one supposed the s ame capacity for all ships of the s ame size and type, whic h could lead to c onsider- able errors due to difference in build.
The second method i s mentioned b y Witsen when quoting his friend Joh annes Hudde (16 28–1704), fellow burgomaster of Amsterdam and renowned mathematician (pp. 241–47). Van Yk also describes this method (pp. 249– 51). It consisted of measuring the difference in the draft of a ship when empty and when loaded, and then c alculat-
ing the capacity of that difference. This method required that the inspector of weights and measures performed the measurements from a boat alongside the ship. Although less labor intensive th an the c annon-ball method, it was still too cumbersome to be ide al.
The third method was an e arly application of the block coefficient, the r atio between the act ual volume of the submerged part of the ship and a b lock of the same length, breadth, and depth. L ength, breadth, and depth were multiplied, whic h gave a tot al volume in cubic feet that was much greater than the actual volume of the ship. This was therefore divided by a factor that had been pre- determined by one of the two methods mentioned above and that varied for each type of ship. The factor adjusted for notional block coefficient and c onverted the volume from cubic feet into lasts. For a variety of inshore vessels the factor ranged from 1 70 to 240 , but factors were also determined for large seagoing ships. Yet, as with inshore vessels, it was impossibl e to apply the s ame factor to all seagoing ships. In the anonymous manuscript Evenredige Toerusting, which deals with men-of-war, the f actor is 250. Hendrick Decquer, who performed an inquiry into the measurement of ships for the Dutch East India Company, arrived at the s ame number in hi s report (c. 16 90), but when we c ompare ships for whic h both me asurements and the number of lasts are known, we fi nd that there were actually wide differences in the ratios (see table 2 in
Introduction
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