Caused by gravity from the sun and the moon pulling on and deforming large bodies of water.
Daily changes in tides:
High tides occur on the side of earth closest to the moon and the side opposite the moon. -
High tides draw water away from the areas between, causing low tides to form. For most places on earth, high tides occur every 12 hours (twice a day). High and low are about 6 hours apart.
Some places on earth have only one high and one low tide everyday. High and low are about 12 hours apart.
-Tides with maximum daily tidal range
- Occur right after the new or full moon, about every 14 days - When the sun, the earth and the moon are in alignment, and their gravities are - Working together to deform earth. - High tide at noon and midnight
-Tides with minimum daily tidal range
-Occur right after the 1st or 3rd quarter moon, about every 14 days -Occur when the gravitational forces of the sun and the moon work against each other -Occur halfway between spring tides
- High tide at sunrise and sunset
The rule of twelfths:
This rule allows us to estimate how the water depth will change between high and low tides. -
Tide charts give us the time and depth of water at the high -
This information will be important if you are trying to navigate a deep draught vessel at times other than high or low tide. -
First you need to work out the tidal range, the difference in height between the high and low water mark. -
To work out the tidal range you take the low tide height away from the high tide height the total height of the tide (tidal range) is then divided into 12 (hence the name). -
Tidal range / 12
We will then use these 12ths to work out how much the tide changes in any one hour. -
The average tide takes approximately 6 hours to get from high to low tide or vise versa. -
The tide does not come in or go out at a steady rate.
It is slowest around high or low water and we say that we have “slack...
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