How Tide Clocks Work

Tide clocks give estimates to the time between high and low tides. While they are called tide clocks, what tide clocks are really doing is keeping track of the Moon's apparent motion around the Earth.

Tides are influenced by both the gravitational forces of the Sun and the Moon. Both these bodies tug on the Earth as it rotates. However, because the Moon is much closer, it tugs about twice as hard. Subsequently, tides are closely linked to the lunar day.

Half of a lunar day is exactly 12 hours 25 minutes 14 seconds which is exactly the time in between high and low tides in most locations. Subsequently, tide clocks are really clocks that work on 12 hour 25 minute cycles opposed to 12 hour cycles. Yes, that means tide clocks do not have some magical gravitational mechanism inside them but rather tide clocks just have a clock that ticks 25 minutes longer.

You may have noticed that we said tide clocks work on 12 hour 25 minute cycles but that the time in between tides is actually 12 hours 25 minutes 14 seconds. What this means is that there is actually about a 15 minute lag each month and a tide clock must be reset each month. The best time to reset the clock is either on the new moon or the full moon.

The West Coast Problem

There's one problem with tide clocks however- while they are reliable on the East Coast they are not as reliable on the West Coast. This is because while the Moon is the biggest influencer in tides, it is not the only influencer.

In a perfect World, the tides would follow the moon as it traveled East to West. However, there are obstacles getting in the way of the free flow of water, mainly the continents of North and South America! This interferes with the tidal bulge and creates some crazy tides on the West Coast. View our article Where Tide Clocks Work Best to see where tide clocks are most reliable.