Similarly, the hull shape defined by La Belle's longitudinal diagonal curves provides guide points for drawing the transverse frame shapes. In La Belle's design system, the offset points for the diagonal curves are plotted at frame positions; therefore, on each frame's conceptual design plane, each diagonal curve provides a guide point for drawing the frame. In other words, the offset points are the guide points (Figure 20t, u).
To completely define the frame shapes, the guide points for each frame must be joined with curves. La Belle has only three diagonals for defining the shape of the lower hull, and there is a significant gap of undefined curvature between the maximum breadth diagonal and the upper bilge diagonal. Therefore, La Belle's designers must have had some rules for drawing the transverse curves between the diagonals. These rules would need to limit/restrict the transverse frame geometry in such a way as to assure a smooth transition in curvature from one frame to the next.
At first, due to a general similarity in shape along sections of the surviving frames, I thought a single template might have been used to draw the curves between the upper bilge and the maximum breadth diagonals on all the frames (Pevny 1999). However, experimenting with shifting templates based on the shape of the midship section did not give satisfactory results when compared to the shapes of the surmarked frame timbers. In addition, no logical sequence of steps could be reconstructed that would allow the designer to shift the templates in order to get similar results.
The method reconstructed for joining the guide points for the after surmarked frames (Figures 20v, 47a–f) applies the same drawing principles as were used in the reconstruction of the midship frame. This sequence of steps for drawing the frames, using arcs of varying radii, can easily be duplicated without any reference to the archaeological timber recordings. In Figure 47f each category of arcs that combine to form the shapes of the surmarked frames is distinguished by a different shade of gray. Note that the lower breadth and bilge arcs on the midship frame extend slightly below the diagonals. This anomaly is a consequence of the centerline offset that impacted on the positioning of the diagonals on the midship frame. The radii of the tumblehome curves differ so slightly that I would presume a common template could have been used to draw them on the timbers if not already in the body plan drawing. The deadrise lines/curves are shown dashed in Figure 47f. Since the drawing procedures for these could not be completely systematized, they are not illustrated in the rest of Figure 47. Figure 20w illustrates how the above design procedures provide the information for defining the shape of frame VIIIID. Figure 20w also depicts the surmarks as they would appear on the forward faces of the timbers of this frame, and how these marks directly reflect the method used to design the hull. NEXT
© 2014 TARAS PEVNY