We are sometimes asked the best way to get rid of hollow waterlines (not that they are always a bad thing). Often the combination of parameters that are used in a hull assistant will lead to hollow waterlines, or other aspects of the hull assistant-generated hull that you'd like to change. This is where direct control point editing comes in. While the hull assistants are very useful for quickly generating a 3D model that is close to your desired shape, they're not intended to be able to create it exactly. That would require so many controls as to defeat their purpose.
A recent post in the Tips&Tricks area of the Orca3D forum shows an example of creating a hull, and then modifying the control net (moving control points, re-orienting a control column, and adding control points) to attain the desired shape. To read the post, click here: http://orca3d.com/forum/index.php/topic,200.0.html