I am sanding with finer paper to get the surface very smooth. Since the rubberbumper makes the total length, it is best to keep the boat on (straight) an edge. Put a staff into the keel box, too expected depth. Measure that in the front and in the back with a true square tool at the back on the table mark, a meter measure, and then with a true square tool at the meter mark mark in front of the boat.

This way the keel depth can be estimated (for people with no access to a measurement tank, this is absolutely necessary).