The correct answer is C) Prior to getting underway. The requirement to log the position of load line marks in relation to the surface of the water in the Official Logbook is stipulated in the Load Line Convention. This must be done prior to the vessel getting underway, as the load line mark position can change due to tidal and draft changes. Logging the information before departure ensures an accurate record of the vessel's load condition at the start of the voyage. The other options are incorrect because: A) logging is required regardless of water type, B) daily logging is not mandated, and D) logging at watch changes is not the specified requirement.