I had written a detailed post on squat effect on ships. You can read that by clicking below link.

5 Questions that can help in understanding Squat effect on ships

In short, squat effect is the decrease in under keel clearance of the ship because of a ship moving in shallow water. When a ship moves in shallow water, there is a low pressure created under the ship because of Bernoulli's theorem.

There are 3 main factors that affects Squat

• Speed of the ship
• Block coefficient
• Blockage factor of canal

Squat must be taken into consideration when calculating the under keel clearance of the vessel.