SQUAT EFFECT

• The squat effect is the hydrodynamic phenomenon by which a vessel moving quickly through shallow water creates an area of lowered pressure that causes the ship to be closer to the seabed than would otherwise be expected.
•  This phenomenon is caused when water that should normally flow under the hull encounters resistance due to the close proximity of the hull to the seabed.Leonardo's law causes the water to move faster in water level (where the section is smaller); according to Bernoullì's theorem, a velocity increasing determinates a low-pressure area so that ship is pulled down. This squat effect results from a combination of vertical sinkage and a change of trim that may cause the vessel to dip towards the stern or towards the bow.
• The squat effect is approximately proportional to the square of the speed of the ship. Thus, by reducing speed by half, the squat effect is reduced by a factor of four.
• The squat effect is usually felt more when the depth/draft ratio is less than four or when sailing close to a bank. It can lead to unexpected groundings and handling difficulties.