ALL ABOUT TIDES AND TIDE MOVEMENT CLOCKS

(Including How To Set Them)

The basics…. What is the tide and what creates it?

In a nutshell, Earth, Moon, Sun, Gravity & rotation. The simple explanation is that the moons gravity pulls the water towards it so as the earth rotates, the water gets pulled from the sides creating a high tide where the moon is closest. As the earth rotates and the moon goes overhead of any given spot on the equator every 24 hours 50 minutes & 14 seconds, so does the high tide. But…

The action of the water being pulled from the sides of the earth means that the water level on the sides drops but that the water round the back of the Earth is still at the original level, which is now higher than the sides, creating a second high-tide, that occurs directly opposite the first high tide.

So Is That All There Is To It Then?....no.

Because the sun is so massive, its gravity too has an effect on the tides and obviously the sun is in a completely different location and cycle to the moon. This means there are times when the moon and sun are in a line with each other which adds all the gravity effects together, and times when they are at right angles to the earth which offsets each other’s gravity effects.

The end result is that the low tides get lower the high tides get higher when the moon and sun are in a line with the earth, and we can also see the opposite where the high tides get lower and the low tides get higher when the moon and sun are at right angles to each other from the earth.

So everyone gets a cycle of 2 high and 2 low tides every 24 hours, 50 minutes and 14 seconds?

No, it was never going to be that simple. If you’re not already getting the impression that this stuff has many, many other factors affecting it, then you will after the next few paragraphs

Tide patterns come in 3 basic forms, although some of the variations we will mention in a minute. Around many of the world’s coasts (including the UK) we get what is called a Semidiurnal pattern, which is two high and low tides a day. A small number of places get just one high and low tide each lunar day (Diurnal) and this is the most uncommon tide type, with the rest of the planet experiencing what is known as a mixed tidal cycle.

So with a tide clock expecting a 12 hours and 25 minute cycle, but in reality getting anything but, what good are they?

From the diagram shown, you can see how the length of the daily cycle increases and decreases dependant on the moon phase. As the lunar cycle passes through the complete cycle, the errors of aligning to the real tide timing get cancelled out, and at several points during the 29.5 day cycle the clock perfectly synchronises.

When the Tide clock is out of sync during the other times in the month, it should only be by a relatively small portion of a single tide cycle, so will still act as a good indication of where the tide is and if it is rising or falling from a simple and quick glance.

So assuming all that made sense or at least was all good, you then bought a Tide clock, and found yourself asking... How Do I Set My Tide Clock?

The best way to set your tide clock is to first check that the tide at the location you have chosen is suitable, i.e. 2 high and low tides per day, averaging out to the 12 hours 25 minutes a cycle. Head over to Tide Forecast (https://www.tide-forecast.com/) and review the location being considered for tracking the tide.

Once on the site and a location has been entered, scroll down to the tide pattern graphic and check out how regular and clean the tide is.

If it looks like below - (Weymouth), you might want to think again.

Ideally, you want your chosen location to experience an even and regular tide with two highs and two lows per day like below:

The next factor to consider before setting your clock is whereabouts in the lunar cycle you currently are. Ideally a Tide clock should be set when a full moon is occurring, but the next best option is when a new moon is occurring, as the coefficient of the tide is highest around then, which gives the clock the best chance at being accurately set. To know what the moon phase is, or to find out when the phase will be a full or new moon, checkout the lower rows in the tide tables at Tide-Forecast.com (Example below)

So hopefully we are now at the point when the time is right, and the place is right, and all we have to do is wait for the 1st high tide occurring after the full moon (or new moon), set the dial pointer to top dead position (equivalent to 12 o'clock on a standard clock), and put the battery in. However, if that tide occurs in the middle of the night, don't worry, just use the next High Tide as the difference in coefficient will be very minimal and will not make a noticeable difference in the grand scheme of things. We recommend that the clock is checked and corrected every 3 months (or 3 lunar cycles to be more accurate) to remove errors from other considerations that do not get factored into the 24 hr 50 min and 14 sec cycle.

IMPORTANT NOTE -

As we have already seen in one of the graphs above, how the synchronisation of the clock to the real tide moves back and forward throughout the cycle, this means you should not adjust your clock because it did not match the exact time of a high or low tide, as this error will be corrected automatically throughout the month if left.

If you do adjust your clock, make sure it is only on either a New Moon (best) or Full Moon (second best alternative) and following the instructions above, to avoid introducing errors that will put the clock completely out of synchronisation to the tide pattern being tracked.

So we mentioned ‘variations’ in the previous paragraph. Numerous factors affect the tide like the depth of water and other geographic features. These can introduce secondary tides which create double high tides and double low tides. And of course not every body of water has enough volume to have a noticeable tidal effect. Did you know that the earth causes a tide on the moon too? But because there is no water there, the tide is actually a bulge in the moon’s dust and rock surface, of some 60 metres high or so. It does not move round the moon like our ocean tides do though due to us always having the same side of the moon facing the earth.

Ok, so moving on, we have established that round most of the UK we have a semidiurnal tide, which means we should be able to track the tide with a tide clock, Right?
Yes...but there is a ‘but’. We know the lunar day is 24 hours and 50 minutes approx., so this principle is what a tide clock uses by rotating a complete turn every 12 hours and 25 minutes. However, very few places have the perfect tide of 6 hours and 12.5 minutes for the tide coming in, and then the same for the tide going out. In fact, nowhere does. The problem comes from the moon and sun interaction causing the difference in timing along with numerous other factors, and we won’t go into seasons and the changes in the distance from the sun having even more effect. If your curious just how messed up the tide can get just around the UK coast lines, check out the daily tide patterns around Southampton’s double high tides, Weymouth’s complex double low tides, or Lowestoft with the result of mixing a notable Diurnal tide with a main Semidiurnal tide.