Caulking is defined by driving oakum, cotton or general rope fibres in the seams of a ship's wooden deck or side / hull to make it watertight. It also plays a structural role in tightening up the hull / deck of a ship and reduces the longitudinal movement of neighbouring planks.
It is very easy to demonstrate the principles behind caulking a vessel, however, it is a skill where practice is important but also individual vessels present their own issues. Usually you will have to warm to the task, understand which iron you have to use, and how much oakum. There is a lot in the skill that simply comes from experience and new builds present different issues to old boats.
The final pitching of the seam was not demonstrated because it was not occurring at the time of the demonstration.
The process is demonstrated in the accompanying video clips with a step-by-step guide. The conversation with the boat builder, in this case, Chris Rees is unscripted and covers the technique from his experience.
The technique is very simple but the subtleties come with experience:
If a seam is stopped midway, leave the oakum attached if possible. If you have to break off the oakum or run out and need to start a new bail / ball, twist the ends together so they become one.