Squat is the decrease in the under keel clearance (UKC) of a ship when it is proceeding in shallow
water.
In the case of large, fast ships, squat can be as much as 2 metres, Squat does not occur when the ship has no movement through the water.
When anchored or alongside, in shallow water, strong tide can cause squat as there is movement of the ship through the water, though there is no movement over the ground.
Empirical formulae for Squat:
Empirical formulae are those that have no scientific derivation but give reasonably accurate results based on practical observations in the past.
The following two simple formulae give values of squat that is reasonably close to the actual values of squat.
In shallow ‘open waters’
Squat in metres = ( Cb x V )÷100 where V = speed in knots & Cb = Block coefficient of the vessel
In shallow narrow channels or canals
Squat in metres =( 2(Cb x V x V)) ÷ 100 where V – speed in knots & Cb = Block coefficient of the vessel.