Page 33 - Nicolaes Witsen & Shipbuilding in the Dutch Golden Age

meaning that they were reduc ed in s ize and were built more for speed. This shift elicited Witte de With’s lament that the entire Dut ch fleet operating in the First Anglo- Dutch War actually consisted of frigates.19
It is possible that this change, induced by the Admiral- ties, occurred with some del ay in the merc hant fleet as well, but it is difficult to find proof to substantiate such a hypothesis. One indication is that in the written sourc es on the Admiralties, the terms frigate and pinas were al- most interchangeable. It is clear, however, that in Wit- sen’s day the pi nas was a rel atively fast and well- armed merchantman, capable of taking on enough c argo to make it a profitable business undertaking but also armed in a way that it could effectively defend against enemies. This must have been why Witsen chose the pinas for his example: it was a design that could illustrate aspects of both the m an-of-war and the merc hantman.20 As Witsen explains:
(263 I 28) The ship which is built here in our mind is neither the widest, nor the narrowest; w hich measure is taken with premeditation, to show a man- of-war as well as a merchantman. Those sailing for freight only, and cannot defend themselves, are narrower above and broader below: those going to war only, are broader at the top and narrower at the bottom.
(53 I 30) Of which the measuremen t and shape are well understood, that from these one can easily derive and fabricate ships of an y length and usage (mutatis mutandis, change what has to be changed), both large and small; because all rules, symmetries and propor- tions remain the same, on all the distances on the keel; when the ship has a keel of one hundred and eighty, or of only sixty feet.
So if we m aster the inform ation on the pin as, accord- ing to Witsen, we have the key to all other types of ships. But Witsen is careful:
(53 I 45) It is true, on the other hand, that to apply the mathematical measurement to its full exactness, is not always possible, as with the man y and varying cur ved and crooked shapes, that one has to apply to the ship’s timbers.
(53 II 36) Material, place and opportunity often cause deviations. The use, w hich is of endless variation, forces the building master to bend rules and mea- sures.
(53 II 26) The more precisel y the proportions and symmetry in shipbuilding are observed, the more per- fect the ship will be, graceful, strong and well-sailing.
(54 I 12) No one expects that all parts of the ship will be shaped to mathematical detail: this will onl y be done for those parts, which are the most important in the ship, from w hich the oth ers will follow without exactness.
Shipbuilding Theory in the Seventeenth Century
A seventeenth-century ship was designed and bu ilt by applying a number of propor tional formulas (see table 1 in the appendi x), which we w ill go into exten sively in chapter 2. A table of such formulas, which Witsen says he obtained from the “famous master shipwright Jan Dirrikze Grebber,” demonstrates that, using these formul as, it is possible to generate a kind of recipe for ships of all sizes (fig. 1.10). Within the boundaries of these formulas the shipbuilder had some leeway, as we shall see. Of course, he started with a general mental image of the vessel, but until the erection of the top timbers he was always open to the possibility of changes, depending on the av ailabil- ity of timber, alterations in plans of the builder or the com- missioner, or other c onsiderations. He also knew pretty well how f ar he h ad to dev iate from the st andard rules to obtain a bulk y carrier or a sh arp frigate. This freedom to deviate from the rules was gained solely through ex - perience, either person al or th at of others, in c onstruct- ing successful ships (or f ailures). There is no ev idence whatsoever that shipbuilders were capable of calculating a ship’s performance beforehand. Even the dr aft of the vessel could be on ly estimated,21 which Witsen’s follow- ing remark so plainly demonstrates:
(180 II 49) Today ships are smeared with a mixture of resin and tallow as far as the estimated draft of the vessel.
In Holland at the time, there was a da wning notion of shipbuilding theor y, but only in the more intel lectual circles, as exemplified by Witsen and earlier by Simon Ste- vin, and not among actual shipwrights.22
Although concepts such as metacenter and c enter of balance did not yet exist, Witsen formulates quite compli- cated arguments for i ssues like the mec hanical effect of the mast on the ship —the mast is a lever . . . (p. 250)— and calculations of the displ acement of the pinas ship. I will return to thi s in the di scussion of tonnage calcula- tions (see “Ship Measurement” later in this chapter). But for most theoretical questions, such as the equilibrium of floating bodies, Witsen does not get beyond theorizing and does not arrive at calculated predictions, as we can see in these examples:
Introduction
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