He was a person who chalked between the planks to make them water tite.
"Caulking Wooden Ships
"The planks of a wooden ship are grooved to allow space for the insertion of caulking material between adjacent pieces. There are several materials used for caulking planked wooden ships. Historically, a fibrous material called oakum was used; today a number of different plastics, known as elastomers, are also available.
Elastomers consist of long, tightly twisted molecules that stretch and recoil, much like a spring. Plastic caulking materials are thoroughly mixed with a liquid curing material just before application, and the combined paste is then injected into the clean seam. The outer surface of the seam is smoothed off until it is level with the adjacent planks. When properly applied, plastic materials are far superior to oakum because they adhere to the wooden planking like glue, and they retain their rubber-like elastic properties indefinitely.
Oakum may still be used for recaulking older ships; it is also used in places where plastics are not available. Oakum is made from old hemp rope that has been untwisted and picked apart. It is generally used in the form of loosely spun yarn and may be untreated (white) or saturated with a tarry substance (black). Oakum comes in balls or in rope form. "