Complex sentence: A Dockmaster is a person in charge of a dock used for freight, logistics, repair, and or maintenance of ships (also known as a shipyard or drydock).
Split into simpler sentences: A Dockmaster is the title ascribed to a person in charge of a dock. This could refer to the docks used for freight and logistics and/or to the repair and maintenance area for ships (also known as a shipyard or drydock).