Fishing vessels have some features that must be considered when splitting into sections of the surface. Race of bottom and building trim somewhat complicate the task of the surface modeling. Consider the two most widely used partitioning options.
In first variant, the fore ship surface is specified without isolating a area of a flat - keeled bottom. This presents additional difficulties when it is necessary to define a flat surface area in the composition of the fore ship. The advantage of this partitioning option is a solid portion of the aft ship main hull surface, with preservation of the continuous smoothness of the surface.
in Second variant flat-keeled bottom in the fore ship is allocated to a separate surface patch. This makes it easy to control the shape of the flat bottom line. At the same time, we must divide the aft ship main surface into two parts. Along the boundary line of the aft ship surface patches, only smoothness in the first derivative will be ensured. Since the aft ship main surface has a rather simple form, I prefer to use this splitting option. Note that here also separated the area of the cylindrical part of surface. It is sometimes useful to do if in the future you plan to extend the body in the area of the cylindrical surface part.
The peculiarity of this method of specifying the fore ship is that the line of the flat - keeled bottom in the fore should lie in the plane of general position formed by the keel tilt line and the bottom tilting line on the mid-section. The line of the bottom is also the lower boundary line of the curved fore ship surface. Therefore, it is convenient to create the bottom plane as a template and project the bottom line onto this plane after editing. Such a plane is also particularly convenient for controlling the entry of frames into a flat bottom.
It is important to note another feature when designing the aft ship of a fishing vessel. The main surface of the aft ship is bypassed by the CL at the point of attachment of the aft skeg and, subsequently, is cut off by a surface line in the CL. That is, the stern of the CL after the skeg is the surface line on the main surface of the stern. The profile line of the skeg in this case is hung on the knuckle line of the skeg. At the same time, the knuckle line serves as the boundary of the main surface of the stern. For the convenience of modeling the skeg, the top point of the skeg profile should be strictly in the knot on the knuckle line. This will give a predictable number of control points on the surface of the skeg and will facilitate the process of giving the skeg the desired shape.