Hi Thomas, also if you want your hull surface to be capped by that cutting line, the way you would do that is to extrude the cutting curve out into a surface that crosses the hull.

Then select both the hull and the extruded surface, and run Edit > Trim. At the prompt to select cutting objects, just right-click or push Done without picking anything else. That signals to Trim that you want to do a "mutual trim" operation where each object is acting both as something to be cut and also as a cutter itself for the other object.

Then that will take you to the next prompt where you can select pieces to discard, you can then pick the exterior areas that you want to remove and then finish the Trim.

After that is done then select both pieces and then use Edit > Join to glue them together into a solid.

- Michael