Low tide and high tide originate from the gravity pull of the moon and the sun, of which the effect of the moon is the strongest. Along our coasts tides occur twice a day. Every 24 hours the water rises and falls twice.
The average period between a high tide and the next high tide is 12 hours and 25 minutes. However, one week the tidal waves come quicker than the other, and after that slower again. These accelerations and slackenings are connected with the mutual position of the sun and the moon. A pure mechanical tide clock would soon be out of pace with the real tide and show a divergence up to even 2 hours! The cause is that a mechanical clockwork only takes in account the movements of the moon. This is not the case with the extremely modern tide clock of Jacob Venker, that has been developed in the Netherlands and to be seen on the outside wall of the National Dutch Towage Museum. This device takes in consideration nearly every tide wave and water movement (The Dutch Department of Waterways and Public Works - Rijkswaterstaat - distinguishes 94 waves, so does the tide clock). This complexity is the reason that this clockwork is run and controlled by a computer, that compensates for more than 95% of the deviations. So, as a result, this clock runs almost perfectly synchronous with every appearing tide. Therefore the tide clock of Jacob Venker at the museum is the most precise one in the world!
Already since 1996 the town council of Maassluis took an interest in a tide clock from Jacob Venker.
Beautiful Maassluis is situated along the busiest waterway in Europe, an open connection to the sea. The town has a harbour of its own and ... high and low tides! At a stone's throw distance from the North Sea you will see the water rise and fall twice a day. Normally speaking a river streams only in one direction. However, a remarkable phenomenon is that the river off Maassluis twice a day for some time flows upward instead of downstream. We will explain how that is possible. The North Sea itself is too small and shallow to generate tides of its own. But all the same the tides occur. And not half! Read more about the origin of the tides of Maassluis and the North Sea.
The tidal wave in the North Sea moves up the river to Maassluis twice a day. These waves originate in the Atlantic Ocean. It begins in Scotland. They reach the Dutch coast the following day. When seen from the air, the tidal wave in the North Sea spins in a whirl around several central points in a counterclock-wise direction. These whirls are caused by the rotation of the earth (Coriolis effect). The center of such a whirl (called the amphidrome) barely moves, so that there is no tidal difference here. The North Sea is influenced by three such whirls: one in the northeast, one in the middle and one in the south. In the Netherlands, the tidal wave arrives first in Vlissingen, moves up north, and only arrives by Schiermonnikoog eight hours later (see graph below). The height of the tide is related to the distance from the center of the whirl. The whirl in the south affects the tidal effect in Maassluis the most. The difference between high and low tide in Maassluis is about 1,50 metres average.
The with double tower gold gilt hand is continuous secanting the edge of this blue surface, thus functioning as a gauging rod. Moving over the clock face this gauging stick will dive deeper or less deep in the blue surface. In case of high tide the hand of the clock will point perpendicularly upward under "HW" (= HT - high tide). In this position it stretches entirely over the blue surface. The water then as it were has risen till the top of the "gauging rod". About 5 hours later (the hand has then moved to the bottom on the right side position) the blue field has sunk along the gauging rod and is fallen almost entirely dry. Subsequently a period of about 4 hours low tide (LW) begins. Thus the rising and falling of the water is easily to read and predict. From the left side to the right also a small red arc through the blue tide form. 3,5 hours after high tide the water level has reached N.A.P. (= normal Amsterdam level = a Dutch standard for the water level). On this moment the hand secants the right end of this arc. Only more than two hours before high tide the water level will have risen above N.A.P. That happens as soon as the left end of the arc is passed. Spring tide is a phenomenon that appears once in a two week's period. It happens always two days after full and new moon. In those periods the tidal wave is higher and somewhat steeper. The water then also rises somewhat quicker. As a result the period between high and low tide will last a few hours longer. The lowest water level is reached when the hand of the clock is in the bottom left position. That moment appears about 7.5 uur after high tide. Slack water occurs when the moon is in one of it's quarter positions. This always will happen a week after spring tide. During such a slack tide period it is low tide when the hand of the clock is pointing perpendicularly downward.
The highest wave is the spring tide curve, the lower wave is the slack (neap) water curve. The Dutch Ministry of Traffic and Waterways (Rijkswaterstaat RIKZ, Rijksinstituut voor Kust en Zee) measures the sea water level on many locations. Not only along the coast, but in the large rivers as well. By using a float, the vertical water movements are recorded on all those locations on a continuous basis. Thus long measure series are provided. Maassluis also has a similar measure point. The accuracy of the tide clock is based among other things on these measurings.
In fact each tide clock has been made in synergy with ancient traditional artisanal clockwork arts and contemporary high-tech methods. For instance, the clock face has been fitted out with gold-leaf gilded Roman digits. But, please note the cut sharp presentation of even the slightest details. This beautiful fine accuracy is the result of a new by Jacob Venker developed method of gilding.
Because the eb and high tides are the result of a complicated interaction of tidal waves, the simulation of these movements require similar complex mathematics. Old fashioned mechanic clockworks cannot handle this and therefore will often show deviations of no less than two hours. The system of Venker's tide clock is managed by a PC, that functions stand-alone with specialised software. That is the reason that the system is constantly running perfectly synchronous with the tide tables of the Department of Waterways and Public Works, reflecting the astronomical tides....theoretically indefinitely in the future. This in our own country Holland by Jacob Venker and Ad de Jong from Sint Anthonis developed tide clock therefore is the most accurate tide clock in the world.
A tide clock is always custom-made. Naturally also this one, fitted out with a rust-proof stainless clock face (measuring a diameter of 110 centimeters!). Because it has been mounted on the front of the beautiful 17th century National Dutch Towage Museum, it has been designed according to the customary styling and colouring in those days. Each tide clock is built in accordance with specifications, that have been documented in consultation with the board or other authorities and are fully adapted to local requirements, regulations and circumstances.
Similar clocks as in Maassluis were built by Venker on behalf of the Dutch Pilot Organization (Loodswezen) Scheldemonden and the Ministry of Traffic and Waterways (Rijkswaterstaat, Directie Zeeland, Middelburg).