Interpreted this way, the narrowing and rising curves defined by the two sets of offsets combine into a single longitudinal run on the hull (Figure 49n). Although a bilge curve running along the surmarks would only become apparent once the frames were raised, I believe, its quantification is a foundational concept of the Mediterranean moulding design method.

Only when the same types of offset sequences for both the narrowing and rising curves are applied over the same number of frames does the combined bilge curve appear as a perfectly straight oblique line when viewed from the ends of the vessel or projected onto a transverse plane as in Figures 49n and 49o. In these examples, the result is a diagonal because La Belle's offset sequence was used for both the narrowing and rising. Similarly, the same series of narrowing and rising shifts at the top of the futtocks combine to define a diagonal that has the same slope and offset spacing as the floor diagonal (the uppermost diagonal in Figure 49o). In this figure identical futtock templates were raised on the port side. Their bilge curves overlap those of the floor templates with the surmarks perfectly aligned.

Since with the non-graphic Mediterranean moulding method there is no body plan in which to first plot straight oblique lines (diagonals), the combinations of rising and narrowing curves more often than not result in an oblique run with a slight degree of curvature. This is because different types of sequences were sometimes used for the narrowing and rising offsets and/or rising was not applied starting from the midship frame. Nonetheless, the general orientation of these runs could still be characterized as diagonal when viewed from the ends of the vessel.

Defining Longitudinal Runs: A Broad Perspective

It is important to note that such diagonal runs are a general characteristic of planking patterns in shipbuilding—in both shell-first and frame-first construction. On most vessels, when planks are bent to conform to the hull shape, they run diagonally when viewed from the ends of the vessel (Figures 46a, 52). This is a consistent and predictable behavior, particularly for planks that are straight before being fitted to the the hull and which are bent on without excessive edge-set—their natural or normal runs (Chapelle 1969:376–377; Pardey 1991:193–196). In my opinion, this makes such runs at distinct or "key" points of shape transition ideal for regularizing or regulating hull curvature during construction.

Intriguingly, on the remains of a vessel built shell-first, the Jules Verne 7 from the end of the sixth century B.C. discovered in Marseille, the planks of the eighth runs (strakes) on both the port and starboard sides have shipwrights' marks on their inboard faces (Pomey 1998:63–64; 2009:57–59) (Figure 53). NEXT