Squat is the reduction in underkeel clearance (UKC) between a vessel at-rest and underway due to the increased flow of water past the moving hull. The forward motion of the ship pushes water ahead of it that must return around the sides and under the keel. This water motion induces a
relative velocity between the ship and the surrounding water that causes a water level depression in which the ship sinks. The velocity field produces a hydrodynamic pressure change along the ship similar to the Bernoulli effect. This phenomenon produces a downward vertical force (sinkage,
positive downward) and a moment about the transverse axis (trim, positive bow up) that can result in different values of squat at the bow and stern. This combination of sinkage and change in trim is called ship squat.
There have been several grounding incidents related to squat and its effect should never go unnoticed. This App takes into account the vessel/channel particulars and calculates the ship’s squat using Ankudinov’s empirical formula, which is one of the most conservative formulas for squat compared to those recommended by PIANC and is particular used in channel depth design. The App also determines the final trim of the ship.
The App determines the channel types (Confined Channel, Restricted Channel, Unrestricted Channel) using Barrass’s equation for ‘Width of Influence’ and comparing it with the bottom width of the channel. It also determines the Critical and Economic speed of the vessel transiting the channel that should not be exceeded.
The App can be used for estimating squat for channel design and operational use. It also takes into account transiting ships in the channel.