The introduction of digital computers in hydrographic surveying has led to a decrease in routine work and an increase in time for decision making. In merchant ships there are likely to be similar benefits, but there are many facets to the introduction of digital computers. The main criterion, if the introduction is to be a success, must be a considerable improvement in the performance of men and equipment when compared with the additional cost of a revised system, including training in its use. There are two main decision-making phases in navigation—voyage planning and watchkeeping; we must therefore consider the assistance that electronic data processing could give to the navigator in providing data on which plans can be evaluated, progress monitored and decisions made.