Tide is very useful for ships:
1. Because of tides the mud and the soil continue to flow out of the river mouth. As a result, there is no deposits of soil on such coastal ports and ships can come in the interior.
2. Big and heavy ships wait for tides in the deep sea. When there is high tide the ships along with the high tides reach the ports. Once they unload the cargo, they again wait for the tides. So, that they can go back easily to the sea. The ports of Kolkata and London are such examples.
