The change in a vessel's draft with speed, as the hull settles and trims while under way. On survey launches it runs from a few centimetres to over a decimetre and varies with speed and loading. It is measured in a settlement and squat test, comparing vessel height at several speeds to a fixed reference, and entered as a speed-dependent table. Ellipsoid-referenced surveys capture it directly in the GNSS heights.
Squat table runs from 3 centimetres at 4 knots to 11 at 9, so hold your speed steady on the lines.
Also heard as
- settlement and squat
- dynamic draft
Related terms
Static draft
The vertical distance from the waterline down to the transducer face while the vessel is at rest.
ERS
Ellipsoidally referenced survey: depths taken from GNSS ellipsoid heights and converted to chart datum with a separation model.
Bust
A vertical or horizontal mismatch between overlapping lines or surveys that exposes an error somewhere.
RTK
Real-time kinematic: GNSS positioning that uses carrier-phase corrections from a base station to reach centimetres live.