What is a Tide Clock?

A tide clock, which is both a useful navigational instrument and an attractive piece of art, is as the name suggests: a clock that keeps tracks of the ocean’s tides. If you’re using a tide clock to tell the time, you’re looking at the wrong instrument.

Tide clocks are all about the moon and the sea. The moon’s gravity (or pull) is the main factor affecting tidal movements. By tuning a tidal clock based on its location (the Eastern Seaboard of the United States, for example), the tides can be tracked.

It’s important to note that for a tide clock to work accurately, it needs to be used in a spot with semidiurnal tidal cycles. Semidiurnal denotes two low and two high and tides of roughly the same size that occur every lunar day (not solar day). When it comes to the tides, you have to get used to thinking in terms of our great big moon.

Not all coastlines are semidiurnal. The U.S. West Coast, in many places, has mixed semidiurnal tides (tides of varying heights), which are more difficult for tide clocks to calibrate.

Tide Clocks
Tide Clocks

How to Read a Tide Clock

When reading a tide clock, try to picture a timeframe of 12 hours and 25 minutes (or thereabouts). This timeframe corresponds to the tidal cycle of a lunar day. On most Chelsea Clock tide clocks, you can see the markings for high tide at the top of the dial, low tide at the bottom of the dial, as well as “mid-tide” markings where the 15-minute and 45-minute points would be on a traditional timepiece.

The good news here is that when learning how to read a tide clock, you only have to pay attention to a single hand (there’s usually only one hand to look at anyway). The time between high tide and low tide is approximately six hours and 12 minutes. When the hand is at the noon or midnight position, it’s high tide. The 6 o’clock position indicates low tide. The numerals in between the high and low tide markings gauge the hours between high tide, mid-tide and low tide. Knowing how many hours remain before a tide comes in or goes out lets mariners prepare for the movement of the oceans accordingly.

Chelsea Clock’s Tide Clock Collection

As you can see, a tide clock is a handy instrument to track the tides. As a general rule, the handcrafted, precision quartz movement tide clocks designed and built by Chelsea Clock are calibrated for the semidiurnal tides found along the Eastern Seaboard of North America (the U.S. and Canada). And while these clocks are practical tools for seafarers, they also make striking handmade gifts for anyone interested in the oceans in general, or the planetary and lunar physics that govern the tides.