How many times a year can perigean spring tides occur?

Perigean spring tides occur when the moon is both new or full and at its perigee, which is the point in its orbit closest to Earth. This alignment amplifies the gravitational effects exerted by the moon, resulting in higher than normal high tides and lower than normal low tides.

The occurrence of perigean spring tides can typically happen about 6 to 8 times a year. This is due to the combined cycles of the moon's phases and its elliptical orbit around the Earth. Each lunar month (approximately 29.5 days), the moon reaches perigee and one of the spring tide phases; thus, the perigean spring tides align to happen roughly during each of these occurrences.

Understanding the factors that influence tidal patterns, such as the relative positions of the moon and the Earth, is crucial in hydrographic surveying, as it affects data collection times, sediment transport, and other related phenomena in marine environments.