A tidal clock? What for?

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In this section you will find technical specifications and descriptions on numerous topics

Advantages of the tidal clock
Setting your tidal clock
What is a tide ?
Accuracy of the tidal clock

Advantages of the tidal clock  

To some extent many coastal activities are influenced by the tides. Navigators, occasional boaters, but also fisherman, swimmers, strollers or nature lovers seek information on the tide status (i.e.: high, low, flooding, ebbing, etc..). The most common way to find this information is to use a tide chart or to listen to local radio broadcasts or to read the local newspaper. Although precise, finding or extracting information is often tedious.

Setup on a wall or inside a boat, the tidal clock provides a fast answer which is precise enough in most cases. If exact data is needed it is nevertheless a valuable complement to tide charts.

Setting your tidal clock Retour
1-  

Set the clock hand to the "High Tide" position. To do so turn the small wheel on the back of the clock above the battery casing.

2-

Find the next Full Moon on your calendar then look for the high tide time for that day for your area (e. g.: in local hebdo or radio station)

3-

At that exact date and time insert your "AA" battery

4-

That's it ! Wall orientation and sea vicinity have no impact on the tidal clock operation. All you have to do is to install your tidal clock where you want it.

5-

If you have problems finding the information in your area contact us, and we will be glad to help you set up your clock.

What is a tide ? Retour

It's both a complex and a simple phenomenon. Simple because it mainly follows the lunar attraction. The moon describing an orbit around earth once every 24 hours and 50 minutes, thus areas with semi-diurnal tides can estimate a high tide approximately every 12 hours and 25 minutes.

Complex because there are other factors which amplify or dampen, to a lesser degree, the moon's usual effect. The main secondary factor is the solar attraction. Even though it is much heavier than the moon, the sun is so far away that it's pull on the oceans, is relatively small, although not negligible. When the sun, moon and earth are lined up, as they are at time of new moon and full moon, their influences combine without modifying the tide rhythm, high tide is higher than normal and low tide is lower (spring tide). When the sun and the moon are at right angles, as they are at the first and last quarter of the moon, the sun dampens the moon's effect and the height of the tide is smaller than normal. Also at these times the effect of the sun modifies the tidal rhythms so that they are earlier or later than average (neap tides).

The following illustration gives a good idea of this phenomenon:

Spring tide
On new moon
Neap tide
On moon in its last quarter
Spring tide Neap tide

Another secondary factor is the marine and coastal topography. The attraction phenomena described earlier are general and applicable to the whole planet. However, the marine and coastal topography of a specific area also have an effect on the rhythm and amplitude of the local tides. Because of this factor, tides are almost non-existent in some areas of the world, and tremendous in other areas. Bay of Fundy is a good example. Here the world's highest tides, close to 50 feet, have been recorded. Finally, factors like strong and sustained winds or a major variation in barometric pressure can also affect the tide's rhythm and amplitude.

Accuracy of the tidal clock Retour

Considering the simple and complex nature of this phenomenon, how can one predict the time of the tide in a given area ? Well, there is the elaborate way, which consist of calculating the combined effects of moon, sun and topography for a given time and place. That's what the national hydrographic services do using a complex and accurate technology. They publish these results annually as tide tables. One must then extract and adjust the data for a specific area and time zone (daylight saving time).

Or there is the easy way, which consist of programming a clock so that it follows accurately the moon's regular cycle (lunar day). This method is not quite as precise as a tide table for certain stages of the "lunar month" (last and first quarters) but it has the enormous advantage of displaying the information at all times, without any intervention. It is also self-adjusting and can be used in the vast majority of areas with semi-diurnal tides.

Once started at the full moon high tide of your specific area, your tidal clock doesn't need any adjustment for the rest of the year. During the year, there will be some discrepancies with a conventional tide table. This is absolutely normal and you should not try to compensate by moving the clock's hand. The observed discrepancy is only temporary and will be automatically readjusted, partly or totally, a few days later, at either the next full or new moon.
The following illustration gives a general idea of the discrepancies observed between a tide table and a tidal clock over a period of one year or 12 full moon:

TYPICAL DISCREPANCY OF A TIDAL CLOCK
Full moon high tides occurrences at Pointe Saint-Pierre (Gaspe Coast) between October 24th 1999 and October 13th 2000

Tide According to Canadian Tide and Current Table, Vol. 2
(EST or Z+5)
According to a tidal clock with a regular and staedy cycle of 12h25min 14,4sec between 2 high tides Cumulative discrepancy with no adjustments
high 24-10-99 13:20 24-10-99 13:20 start
high 23-11-99 13:45 23-11-99 13:43 0:01
high 22-12-99 13:25 22-12-99 13:17 0:07
high 20-01-00 13:12 20-01-00 12:50 0:21
high 19-02-00 13:50 19-02-00 13:14 0:35
high 19-03-00 13:35 19-03-00 12:48 0:46
high 18-04-00 13:57 18-04-00 13:12 0:44
high 18-05-00 01:44 18-05-00 01:10 0:33
high 16-06-00 01:22 16-06-00 00:44 0:37
high 16-07-00 01:36 16-07-00 01:08 0:27
high 15-08-00 01:52 15-08-00 01:32 0:19
high 13-09-00 13:51 13-09-00 13:30 0:20
high 13-10-00 13:55 13-10-00 13:54 0:00

As can be seen on the illustration, the discrepancy is at its maximum six months after starting the clock, and then, comes back practically to zero at the end of an annual cycle.

As for discrepancies within each lunar month or from one full moon to another, they are in general much less noticeable during full moon and new moon periods (spring tide) and more noticeable during the first and last quarters (neap tide). Over this same yearly span of twelve full moon cycles starting on October 24th 1999, totaling 687 high tides, the following table gives a general idea of discrepancies compared with a tide table :

DISCREPANCY BETWEEN CLOCK AND TABLE
AT ALL HIGH TIDES DURING A CYCLE OF 12 FULL MOONS
OR 687 HIGH TIDES
(at Pointe Saint-Pierre, Gaspe Coast)

between 0 and 30 min. between 31 and 60 min between 61 and 85 min.
384 226 77
approx. 6 out of 10 times approx. 3 out of 10 times approx. 1 out of 10
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