What is Bow Cushion and Bank Suction Effect in narrow channel for ships?

In other words we can explain this as:

Bow cushion and bank suction effect:

• Occurs in narrow channels near proximities of banks.
• There is a tendency for the bow of a ship to be pushed away from the bank, called bow cushion.
• The ship moves bodily towards the bank, which appears at the stern, called bank suction.
• Caused by the restricted flow of water on the bank’s side.
• Velocity of water to the bank increases and pressure reduces.
• Results in drop of water level towards the bank.
• As a result, a thrust is set up towards bank.
• A vessel approaching to the bank will have to apply helm to the bank and reduce speed to prevent the sheer from developing.

Points to pounder:

The cushion is caused by the increased water pressure at the bow, the suction is caused by the decreased water pressure at the stern.