4 minute read
This is a question we often get asked and it's a fairly straightforward question to answer, once you understand a bit more about how tides and tide clocks work.
A tide clock is essentially a dial (just like a time clock) with a timed mechanism. The key differences are the time it takes for the hands of the clock to rotate, and the markings around the edges.
Rather than the mechanism rotating once every 12 hours, like a regular clock, the mechanism rotates once every 12 hours and 25 minutes. This is roughly the time that passes between two high tides. This tells us that there are just under two high tides and two low tides a day.
In the position where a time clock would have the number 12, a tide clock has the words 'High Tide', and in the position where a time clock would have the number 6, a tide clock has the words 'Low Tide'.
Working clockwise from High Tide at the 12 o'clock position, the tide clock shows the tide falling until you reach Low Tide at the equivalent of 6 o'clock. Continuing clockwise, the clock then shows the tide rising from the 6 o'clock position until you get back to the 12 o'clock position.
Here at ClimeMET, we also offer a tide clock with the more traditional 'High Water' and 'Low Water' wording, which is available here.
The moon's gravitational pull generates tidal force which is responsible for the first high tide of the day. The second high tide of the day is caused by the centrifugal force of the Earth and Moon orbiting a common centre of mass.
During the new moon and the full moon each month, the sun, the moon and the earth come into alignment, increasing the pull on the tides to the maximum. In effect, the gravity of the sun reinforces the gravity of the moon. Given this, tide clocks should be set up (or reset) on the new moon or full moon, ideally around noon or midnight, for greatest accuracy.
As mentioned, most tide clocks work on a timed mechanism of 12 hours and 25 minutes but in reality, the tides follow a pattern closer to 12 hours 25 minutes and 14 seconds. This doesn't sound like much of a difference, but 14 seconds per tide can add up to around 15 minutes a month, and would mean that your tide clock won't be as accurate as it once was, so even for the most regular of tides, we recommend resetting your tide clock against a tide table from time to time.
When a customer gets in touch with us at ClimeMET and asks us if we think a tide clock will be suitable for their location, here's what we do:
As well as looking at the tide times online, it's worth looking at the location on a map and seeing what the surrounding coastline looks like, as this can provide a lot of insight. There are some tides in the UK and abroad that don't fit a regular pattern and often tide clocks aren't suitable for customers in these areas. A couple of examples:
Southampton is home to a fascinating double tide, which is explained wonderfully by the ABP. This also affects the Isle of Wight.
The River Thames has tidal parts. In open water, the tide tends to come in and go out at roughly the same pace, but the friction caused by the river bed often means that the tide comes in at one speed, and goes out much more slowly, making it harder to track.
Our complete range of ClimeMET Tide Clocks can be viewed here.