The first two examples, "Keel with 5 control points" and "Keel with 6 control points", are suitable for a sailboat or a modern yacht. The second example is similar to the first one, but with one additional control point. Adding one more control point makes the keel line flatter. You can add even more control points if you need finer control over the shape.
The "Keel for a motorboat" example includes space for the propeller. The last example, "Classical keel for a traditional yacht", is intended for a more traditional hull form.
These keel shapes can be created with any of the four BoatCAD wizards for NURBS boats. Watch the videos for more details.
You can create a small propeller arc sized only for the propeller, a larger arc, or use the arc itself to modify the shape of the keel.
In the generated Excel file, the arc is represented by 50 points. You can use these points to define or refine the keel geometry.
In practice, you usually need only part of the curve to become straight. Start with Step 1 and continue through the following steps. Click the "Add" button to insert additional control points. The more control points you place along the straight segment, the longer and straighter that part of the curve will become.