For example, in Figure 43b, all of La Belle's after diagonals are drawn with only the midship frame and the transom depicted. Conceptually all these diagonals in the body plan (Figure 20p) define diagonal planes from the midship frame to the transom in the stern (Figure 20q).
With La Belle's after diagonals defined, their lengths can be applied to the reconstructed equilateral triangle in order to mark them with curve offsets (Figures 20r, 39). All of La Belle's after diagonals, as in the Toulon flute draft, were applied to the equilateral triangle parallel to the baseline. The offset increments were then transferred onto the diagonals in the body plan (Figures 20r, 44a). As was shown for the floor diagonal, each diagonal's offsets define a longitudinal curve on an inclined plane (Figure 20s). Together these curves define the major characteristics of the curvature of the side of the vessel abaft the midship frame, in much the same way as the longitudinal ribbands help define the hull shape in ribband methods of construction (Figure 15a–c). The difference of course being that La Belle's quantified ribband plan is the central part of the design process and not the initial stage of the construction sequence.
In the sheer plan of the Toulon draft, the longitudinal curves of the diagonals are literally represented as wooden ribbands defining actual curves on the hull's surface (Figure 7). In terms of design, this indicates a clear conceptual link between a two-dimensional graphic entity—the diagonal—and a three-dimensional object—the ribband. In La Belle's construction, this interrelationship between lines of design and actual timber curves is also apparent in the hull structure. Two hull strakes as well as two ceiling strakes essentially follow the same curves as La Belle's two bilge diagonals. The two ceiling strakes are stringers, easily distinguishable from the others because they are notched for the frames. There is little doubt that the shipwrights determined the placement of these strakes with reference to the design diagonals (Figure 45). In fact, in laying out the bottom ceiling planking, the shipwrights seemed to have just filled the space between the lower stringer and the keelson (Figure 45).
However, it must be kept in mind that La Belle's diagonal design curves are idealized ribband runs. In physical reality, as straight ribbands or planks are bent onto a hull without being forced edgewise—i.e., a normal run—they usually exhibit some curvature when viewed from the ends of the vessel (Figure 46a, b). Thus these normal runs exhibit what is known as double curvature. In contrast, in La Belle's design each of the diagonal curves before and abaft amidships has its curvature confined to a single diagonal plane.
Drawing the Frame Shapes
In shell-first construction, the shell of longitudinally oriented planks provides the information needed for shaping the transversely oriented framing timbers. NEXT
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