Which factor contributes to fatigue while operating a vessel?

Operating a vessel can be physically and mentally demanding, which can lead to fatigue. The heat of the sun is a significant factor contributing to fatigue as it causes the body to work harder to regulate its temperature. Prolonged exposure to direct sunlight raises the risk of dehydration and can lead to overheating, which detracts from the operator's ability to focus and function efficiently.

While wind speed, sea state, and water clarity might affect the overall experience of operating a vessel, they do not directly lead to the same level of physical fatigue as the sun's heat does. In contrast, being exposed to high temperatures requires more energy and can lead to quicker onset of fatigue, making it essential for operators to take measures to protect themselves from the sun and stay hydrated during their time on the water.