The History of Tide Observance
Changes in the tides refer to the periodic rise and fall of sea level due to the gravitational pull of the moon. For those who live and work closely with the sea, monitoring tides has always been crucial. According to the National Oceanic and Atmospheric Administration, their historical records from tide and water-level stations transcend the maritime history of the United States—“from the days when clipper ships relied upon tide predictions to navigate ports and harbors, to modern-day mariners that obtain real-time water levels to ensure that water in channels and under bridges is of sufficient depth to allow huge ships and crane barges to pass through.” Furthermore, commercial and Naval wharves, bridges, seawalls, pipelines, and many other major engineering marvels are designed with the tides in mind.  People like fisherman and surfers must plan excursions based on tide predictions, while architects and construction managers are bound to interpreting tide information when working on coastal properties.


How a Tide Clock works
Tide clocks have only one hand, and a cycle of about 12 hours and 25 minutes, which coincides with the rise and fall of the ocean’s tide. Generally, there’s an average of about 6 hours and 12 minutes between high and low tides. High tide is indicated when the clock’s hand is at the traditional 12 o’clock position, while low tide is indicated by the 6 o’clock position. These points of course don’t represent the hour at all, but rather serve as convenient reference points on the dial. However, hour markings between the high and low tide indicators on the clock represent the number of hours that have passed since the last high or low ride, plus the hours before the next high or low tide. Tide clocks require resetting about every 4 months, depending your geographic location. Our tide clocks work best on the East Coast of the United States and Canada.


How a Tide Cycle Works
As mentioned, our moon causes the rise and fall of the tides. About 24 hours and 50 minutes passes between the moon’s appearance in the night sky each night, and this period of time is referred to as the “lunar day.” A tide-clock hand completes its rotation once every 12 hours and 25 minutes, which amounts to twice each lunar day.  There are three basic tidal patterns that can occur along the Earth’s major shorelines. Most shores experience two high tides and two low tides each day. When both of the highs and both of the lows are roughly consistent heights, this tidal pattern is referred to as semidiurnal or semi-daily tide, and is typical on the East Coast of the United States. When the heights of the high and low tides differ, however, the tidal pattern is called a mixed-semidiurnal tide. The West Coast of the United States tends to experience mixed-semidiurnal tides. Of course in some areas, such as the Gulf of Mexico, there’s only one high tide and one low tide per day — and this pattern is simply called diurnal tide.


How to Set a Tide Clock
To set your Chelsea tide clock, follow these simple steps:
• Depending on the model of your Chelsea, you may need to either unscrew the front bezel and remove the dial unit, or open the hinged bezel to access the movement
• Turn the black knob on the back of the movement to adjust the hand to reflect local tide conditions
• Replace the dial unit and screw the bezel back onto the case, or close the hinged bezel