Sea Tides

Tides' might and regularity is remarkable. A sailor needs to be extremely aware of their behaviour and perculiarities, because it is crucial to decisions they make while in coastal areas. Tides are caused by the gravitation of the Moon, which goes around the Earth. In most of the world, tides are semidiurnal (that means twice a day), with two absolutely the same highs and lows. The west coast of North America has tides of mixed type - one with higher high and the other with lower low. Along the Gulf of Mexico tides take place only once a day.
The gravitaional pull of the Moon (aided to a certain lesser extent by the Sun) combined with the centrifugal force on the opposite side causes the tide. As the Moon goes around the earth, it drags a volume of water together with it. The Sun's influence on the whole phenomenon is that during the interaction with the Moon it determines the range and the difference between subsequent high and low waters. Greatest ranges (more than 20% higher than the average) take place in the spring.
Tides and currents are not directly related, though they might look quite similar.
The tide has a stand - a period of no vertical motion.
The length of the tidal cycle follows the earth rotating. Semidiurnal tides alter every six hours and twelve minutes, producing a tide, which are are get later each day.
There are very helpful so-called Tide Tables - they give you information about the tide's range, height, and what is most important - the exact time (to the minute). Be careful! You have to take into acound onshore/offshore winds, local weather and currents, because they will surely influence the situation.
The heights included in the Tide Tables do not represent the actual depth of the water, they are figures to be added - they are simply figures that should be added or subtracted to certain numbers - usually drawn on some visible place, like in the harbour. The charted depths together comprise a plane of reference called the datum line. After 1987 all charts must follow the so-called MLLW (Mean Lower Low Water) system. It represents the average height of the lowest low tides.
So, to predict depths between high and low tides, you should use the so-called Rule of Twelfths. The rate at which tides come and go is not absolutel regular (equal). You have to divide the tide range by 12 and then use the Tide Scale. You will get five intermediate stages of depths and times. To learn the depth at any moment, take the figure from the rule and combine it with the depth of water for the time in question of the previous low or high tide. The other important level is MHW (Mean High Water) - that's the average high water level. Vertical clearance is crucial when you tackle bridges or overhead wires - but you must check the height of your mast in advance - as precisely as possible. As a matter of fact, you need to check all the measures of your vessel - the waterline length, the wade, the width, the centre of mass and some other important figures.
Treat tides with respect, because they can do much damage to your boat. Consider and carefully calculate what the length of the anchor boat should be, so that she is protected from the docks or other yachts. A good indicator as to whether tide is going up or down is the mark - on beaches or harbours - if the marks above the water line are dry, it is rising; if the marks above it are yet - the tide is falling.
There is a moment of silence, as if time stops for just a while - and there is this spooky saying tide carries away the souls of dead sailors to rest in the sea.