Spring-neap cycle and equinoctial cycle explained
The relative motions of the Earth, Moon and Sun cause the tides to vary in numerous tidal cycles – the two most important ones being:
The spring‐neap cycle – a 14.77 day cycle resulting from the tidal influence of the sun and moon either reinforcing each other (called spring tides, although this has nothing to do with the season) or partially cancelling each other (neap tides).
The equinoctial cycle – a half yearly cycle caused by the tilt of the earth, and its orbit around the Sun which leads to higher than average spring tides around the time of the equinoxes (March and September) and lower than average spring tides in June and December.
On average, the spring tidal currents are around twice as fast as the neap currents. However as power generated is proportional to the cube of the current speed, a spring tidal current can generate around 8 times the power of a neap tidal current.
Spring tides usually occur 1½ to 2½ days after full and new moon, with neap tides
experienced just after the first and third quarter (when half the moon is visible).