According to VAN YK (p. 77), these boards are not called “centen”, but “certen”, because the form of the vessel is fixed by means of these boards and made “certain”. Other authors pretend that the word comes from “Kanten” or “Kenten” from the word “bekendheid” (knowledge).
The shape of the ship was thus determined by trial after having settled, in the first place, on the main frame and the length. The smaller the vessel, the more sheer it had and the more ribands were required exactly to determine its shape.
On the other hand it was customary to give the ship some sheer (zeegte), that is: to make it higher at the ends than at the middle. This sheer was obtained, after setting the ribands, by means of sheerstrakes of which the fastening was begun at the lowest point of the height of the ship. These sheerstrakes rose forward at the rate of 1 inch for every 6 feet of length, and aft at the rate of 5 inches for every 6 feet. The wales which served to protect the ship were laid according to the sheerstrakes. The sheer in large vessels (spiegelschepen) was gradually reduced and the effort was made insensibly to build ships with a flat deck in imitation of England and later of America. The sheer still exists in boats for inland waters, like the “Tjalken”, “Poonen”, etc. Only one wale or bend is used for small vessels, the larger ones, such as the “Tjalken” and “Smakken” require three bends superposed.
It is noticed, as a rule, that the bends became lighter in the XVIIIth century, just as did the sternpost and the stem. The engravings which show boats prior to 1500, show also several equidistant bends, and it was only at the end of the XVIth century that the single bends of later days are seen to appear. Moreover, it is certain that the improvement of the navigable highways was one of the causes of the lighter construction of ships.
These old engravings show that the planking is in very short pieces so as to avoid marked curves; but, in order to give, all the same, sufficient stiffness to the vessel, many bends became necessary.
In the old shipbuilding, where the pieces of the planking nailed together clinker ways make the construction more solid, the bends were exceptional. The old “Koggeschepen” (Cogs), for example, had none, but the reproduction of a small boat preserved at the church at Diemer shows them.
These wales are then supported by round wooden brackets which are still found in a few old “Poonen”.
In the matter of the wales, the rule was that when the vessel was seen from in front they seemed to be convex, with the convexity on top, whereas, seen from the side, they look concave, that is, with the convexity underneath.
It has been said in what precedes that the method of ribands (“centen”) was abandoned for large ships, about the middle of the XVIIth century, and that, after that time, work was done from sketches in putting up the frames and in building the ship.