Question 1033Navigation General

The correct answer is D) Wave period. While on a moving vessel, it is difficult to accurately measure the wave period, which is the time it takes for one wave to pass a fixed point. This is because the motion of the vessel itself can affect the measurement of the wave period. In contrast, temperature, atmospheric pressure, and relative humidity can be measured with reasonable accuracy on a moving vessel using appropriate instruments. The other options (A, B, C) are weather elements that can be measured more reliably on a moving vessel, as they are not as directly affected by the vessel's motion as wave period measurements would be.