At what interval should a fix or running fix be taken according to the rules of DR?

Fixes or running fixes should be taken once per hour as part of standard navigational practices to ensure that the vessel's position is accurately tracked over time. This interval provides an adequate balance between maintaining situational awareness and allowing sufficient time for each position assessment to be reliable. In maritime navigation, it's crucial to update positions regularly to account for any course changes, set and drift, and other variables that could affect the vessel’s track. Taking a fix hourly helps keep track of navigational progress and enhances safety by allowing for timely course adjustments.

While taking a fix every course change or every line of position (LOP) can be beneficial in specific situations, the practice of taking a fix at least once per hour allows for a more systematic and manageable approach to navigation. Additionally, tying fixes to operational shifts isn't the most efficient method, as navigation status needs to be maintained continuously regardless of personnel changes. Therefore, the once-per-hour interval is the recommended standard for effective navigational practices.