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Process of Tidal

The moon revolves around the earth once every 24 hours 51 minutes, if other factors are ignored then a location on the earth will experience twice tide and low tide twice a day known as pairs of double (semi-diurnal tides), where each cycle highs downs will shift backwards for 51 minutes every day. Because the trajectory moon around the earth is elliptical, in which the Earth is at the center point, then the distance to the moon change at any time.

The furthest point from the moon to the earth is called Apogee and the nearest point called perigee. Although changes in the Earth-moon distance is small, but because of the large tidal generating force is inversely proportional to the square of the distance, the role of this important change in the distance to the post. At the position of the new moon and the full moon, a moon of the tidal influence is reinforced by the influence of the sun, where the pair posed immense and iniah called spring tide (spring tide).

If the position of the sun-earth-moon forming an angle of 90 degrees, the influence of the month reduced by the influence of the sun, so the pair posed a very small called neap tides (neap tide). The time needed from the tide to neap tide is not always the same as the time it takes from tide to tide. The distance the average time spring tide to the next spring tide is 14.7 days.

Figure 13. Mechanism tide

Tidal range (tidal ranges), the height difference of water at high tide with a maximum height minimum water at low tide, the average ranges from 1 meter to 3 meters. For example, in Tanjung Priok only about 1 meter, about 2 meters Ambon, Chart Siapi-fire about 4 meters, while the highest in Digul River estuary and Strait of Muli in Irian Jaya can reach about 7 to 8 meters. Natural factors that can affect the tides, among others; bottom, the location of continents and islands as well as the influence of the Coriolis force.

Bottom, especially in shallow water, slowing the propagation of tidal movement, so that a place can have a great Lunital interval. Prisoners can also dampen energy base pairs, resulting in certain waters pairs is very small. Beach or island may cause breakage (refraction) or reflection (reflection) tidal wave. Similarly, the Coriolis force can alter the propagation pairs (Boyd, 1982).

Due to the phenomenon of damping, breaking and reflection, then plug the component changes are not the same. Some places such as only experienced a rising tide of the times, while elsewhere occurs twice pairs and some a combination of both these phenomena. Judging from the movement of the sea surface, the ups and downs in Indonesia is divided into four types, namely;
a) a single daily tides (diurnal tide), which occurs one time tide and low tide once a day, for example in the Strait Karimata.
b) the daily tides double (semi-diurnal), which happens twice a day and downs in, for example, in the Strait of Malacca and the Andaman Sea.
c) Tidal mixture leaning to double daily (mixed prevailing semi-diurnal tide), which happens twice a day in different low tide is high and the time, for instance in the waters of eastern Indonesia.
d) Tidal mixture of single-leaning daily (Mixed prevailing diurnal tide), which occurs one time tide and low tide one day very different in height, and time, for example on the south coast of Borneo and the northern coast of West Java.

Knowledge ups and downs in the world of sailing is very useful, especially if you know the schedule of the tides in a port, it is easily a boat can enter and leave the port. Similarly, the energy generated by tidal currents in large quantities can be used as a power plant.

While specific in world fisheries, tidal phenomena can be used to catch the fish types coast by using traps, such as traps and sero. Similarly, this phenomenon can be exploited to perform the replacement of the water in the pond.