Refining Hull Form by adding Curves

Here we see that we have a complete, though not ideal, hull form (see Figure 3:142 in Creating a New Network). From this hull form we can judge where further curves should be added to the network. These curves can come from the existing set of lines. Alternatively they can be new curves created from intersecting the lines set with a plane to create a section, say, or from projecting a 2D curve onto the lines design and extracting a new 3D curve (see Curve Creation).

Having regenerated the hull form we should examine the quality using isophotes. The isophotes should flow smoothly over the patches and particularly across the boundaries of the patches. If there are any areas that appear particularly unfair then it is most likely that either additional boundaries should be included or existing boundaries should be modified or replaced. Below we see the effect of adding an extra curve.

Figure 3:143. Initial surface failing to hold the required shape.

Figure 3:144. Additional curve added to hold shape

Most of the curves included in the network are sections, waterlines or buttocks. Sometimes in some regions of the hull form it may not be obvious which, if any, of these curves are most suitable to describing the shape of the hull. It is for this reason that the user of PACE is encouraged to experiment. The speed at which curves can be added and subtracted from the network and the surface regenerated is an extremely important feature of PACE and is what makes experimentation so easy.

One example of this experimenting with curves is given below. As one can see the section curve in Figure 3:145 below is replaced with a buttock in Figure 3:146 below. It can be seen that continuity across the boundary is improved. It is more desirable where possible to improve the quality of a surface by a better selection of boundary curves than to simply increase the number of curves. This approach results in fewer patches and a fairer surface. Whenever possible it is advisable that the constructed patches have approximately parallel sides.

Figure 3:145. The initial surface using sections as patch boundaries

Figure 3:146. Surface using buttocks as patch boundaries

It may be the case that a surface can be improved by replacing part of a curve with the part of another curve rather than replace the whole curve. An example of this is in the region of the bilge where undesirable long thin patches can sometimes be created. In the figures below it is seen that a part of a buttock has been replaced by part of a section curve. This has resulted in an improved patch configuration by avoiding a long thin patch (see Figure 3:147 below). This is best achieved by making the unwanted regions of curve inactive - see Using Split Points.

Figure 3:147. Use of partial sections/buttocks