A well-done caulking job is key to the construction of a planked boat. When a boat is built, caulking material—typically cotton, hemp, or oakum--is tightly wedged between the planks using a caulking iron and mallet. A seam compound, or in the case of a fish boat, cement is then used to seal off the seam. The process takes both skill and patience.

When the boat goes in the water, the wood planking swells and the caulking material is squeezed in between, creating a watertight seal. Properly caulked seams are critical to the structural integrity of the hull, providing friction between planks and strengthening the framework.

Over time, the caulking materials can deteriorate and harden. The old caulking needs to be reefed out and replaced in order to maintain the boat’s watertight integrity.