Recently, pressure on port authorities to improve port efficiency is increasing due to port competitiveness. Multiple activities within a port influence the efficiency of a port. In this research, the processes of the 'nautical chain' are considered. The nautical chain consists of piloting by a pilot, positioning by tugboats and (un)mooring by boatmen. The provided services are dependent on each other, which makes information sharing between the actors of the nautical chain essential. Enhancing information sharing in the nautical chain could provide opportunities for efficiency improvements. However, current literature does not provide any details on information sharing in the nautical chain. Consequently, it is unknown what parts of the information sharing might be crucial to focus on for improving its efficiency. This research aims to fill this gap, by researching the information that is shared in the nautical chain of the Port of Rotterdam in the delays that frequently occur through expert interviews and observations. The information that is shared in the frequent delay situations is considered critical for efficiency improvements, because the shared information contributes to decisions that reduce the cascade effect of a delay trigger. Following from the identified information sharing in the frequent delays, the areas of critical information sharing are distinguished.