Page 38 - Nicolaes Witsen & Shipbuilding in the Dutch Golden Age

Chapter 1
the appendix). As can be expected, fluyts, with their small crews and light armament, show the most advantageous factor: about 200. Most East Indiamen and w arships have a factor of 250, whereas war yachts, which had little cargo capacity and a burden devoted largely to armament, sometimes reach 350.
On pages 34 to 36 of his appendix Witsen describes an experiment from 1647 in which the measurements of three ships of different ages—new, middle-aged, and old—were compared. The factors for these ship s were determined to be 2 316⁄7, 2391⁄5, and 2 56 respectively, an aver age of 242, after which the Skippers were handed their Mea- surement certi cates, and the Tolls [ . . . ] had to be paid (appendix, 36 II 16). The measurements were used in calculating the tolls to be paid and were br anded on the stem, sternpost, or main beam.
This leaves us with the question of why Witsen pres- ents us with his impressive calculations of the upw ard pressure and weight of the pinas. As we have seen, the erudite Witsen had considerable knowledge of foreign authors writing on shipbu ilding, and F ournier’s Hydro- graphie seems to h ave impressed him most of all. It is possible that, to c ast a sc ientific aura over Dutch ship- building in g eneral and hi s own book in par ticular, he deemed it necessary to demon strate his theoretical knowledge—only half-digested—with these sample atyp- ical calculations.
At the beginning of the seventeenth c entury both the Dutch East India Company and the Dutch Admiralties reg- istered the s ize of a ship in l asts rather than its length. Many have tried to establish a method for deducing length from a given me asurement in l asts, but such endeavors can prove treacherous. In hi s article on the dimen sions and units of Dutch ships, Van Bruggen lists five ships whose length he gives as 90 feet, but the number of lasts ranges widely: 68, 7 5, 80, 150, and 180! Lik ewise, three East Indiamen mentioned by Van Dam, 130, 138, and 150 feet in length, all measured 300 lasts.27 And what about Abel Tasman’s ships? The war yacht Heemskerck had a capacity of only 60 lasts and was 106 feet long, whereas his second ship, the fluyt Zeehaen, with a capacity of 100 lasts, was only 100 feet in length.28
It seems, then, th at not only were the u nits of mea- surement inconsistent in those times but so too were the motives in est ablishing the c argo capacity. To try to de- termine the length of a ship for which only the number of lasts is known remains a hazardous undertaking.
From the displacement diagram made by the Scheeps- bouwtechnisch Ingenieurs Bureau in Bloemendaal and the calculated weight of the pi nas as a whol e, computer
calculations put its displacement at 635 tonnes at a draft of 12 feet (which must have been about the maximum).29 If trimmed b y the stern w ith a m aximum draft of 12 feet, the tonnage comes to 586.
The ratio between cargo capacity and displacement can then be established as 0.55, which means that the pinas could carry almost as much cargo as its own weight:
(317 II 37) A ship, says Fournier, a French Author, car- ries as much as she weighs herself.
Sailing Square-Rigged Ships
Gerald A. de Weerdt
Witsen himself was neither a shipwright nor a s ailor. Yet his remarks on matters such as rigging and sail handling are far from theoretical fantasies. Apparently he was well informed by real experts.
Sails
The sails of seventeenth-century square-rigged ships were not cut with optimal aerodynamic curvature like they are today. The square sails were simply composed of straight widths of textile (the so-called cloths), resulting in a com- pletely plane canvas. For the greatest efficiency the wind was allowed to push some cur vature into the s ails, for which the head r ope was given some slack when it was tied to the yard:
(139 I 50) The Sails should not be too tigh t nor too at against the Yards, but in such a way that, the wind blowing into them, it will give it some roundness; and
thus the wind is better caugh t in the Sail , and can transmit more of its movemen t to the canvas, and the Ship’s progress shall improve.
It was the common opinion of sailors that the foremost sails, those of the foremast and the bowsprit, yielded the best effect—which was probably true, as the ships were built and rigged to sail on a re ach of no more th an two compass points (22.5 degrees) closer to the wind than a beam reach. Many paintings and engr avings show th at the foresails were the last to be reduced.
(139 II 5) The Sailors agree, that the foresails are the ones giving the Ship most of its momentum; giving for a reason, that the wind will apparently draw forth the Ship; and will onl y push aft and in the middle: also that the wind in the foresails will cut through the Sea in a better way, the waves being nearer.
(The last argument is of little value and should not be taken too seriously.)
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