Final answer:
In the context of navigation at sea, it is important to use pilotage and dead reckoning to determine your position when other navigational aids are not available.
Step-by-step explanation:
In the context of navigation at sea, it is imperative to check your position using pilotage and dead reckoning in case other navigational aids fail or are unavailable. Pilotage involves using visual references such as landmarks, buoys, and lighthouses to determine your position relative to known locations. Dead reckoning involves estimating your current position based on a previously known position, taking into account factors such as speed, course, and time.