What are the main factors that affect navigation at sea?

The main factors that affect navigation at sea include weather, currents, and visible landmarks.

Weather is a crucial factor because it can change quickly and significantly impact visibility, wind patterns, and sea conditions, all of which can alter a vessel's navigation trajectory. For example, fog can reduce visibility, while storms can create hazardous conditions, requiring careful navigation adjustments.

Currents are also essential to consider, as they can influence a vessel's course and speed over ground. Understanding and anticipating current patterns is vital for effective navigation, particularly when planning routes and coordinating with other vessels.

Visible landmarks serve as reference points for mariners, allowing them to confirm their location. This becomes particularly useful in coastal navigation or when entering or exiting ports. The ability to identify and interpret these landmarks helps ensure safe and accurate navigation.

While the other choices mention factors like vessel size and crew experience, which certainly play roles in the overall navigation process, they do not encompass the immediate and influential elements critical for navigation as effectively as weather, currents, and landmarks.