Definition
In shallow water the accelerated flow beneath the hull lowers pressure, so the vessel bodily sinks and changes trim, cutting under-keel clearance exactly where it is scarcest. Squat grows roughly with the square of speed, so halving speed reduces it to a quarter. A common approximation is block coefficient multiplied by speed in knots squared, divided by 100 in open shallow water or by 50 in a confined channel, giving squat in metres.
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