In this study, a CFD analysis was conducted on the squat characteristics of each hull form to evaluate the navigation safety of very large vessels in shallow water. CFD simulation was carried out for full-scale vessels with a high Rn. The KRISO very large crude-oil carrier and the Duisburg test case for a 14,000-TEU container ship were selected for the simulation. Based on the numerical simulations for these vessels, the sinkage and trim characteristics in shallow water were analyzed and compared between the tanker ship and the container ship. In the case of DTC, the ship speed had more effect on sinkage than trim. As the pressure decrease at the vessel bottom occurred near the center of the hull, trim did not change much. KVLCC2 had higher sinkage and trim values when the water depth decreased and the ship speed and drift angle increased. KVLCC2 showed trim near the bow, where the bow sinks.
In a study by Quadvlieg and Van Coevorden (2003), it was reported that about 90% of vessels worldwide sail in shallow water.
When a vessel sails in shallow water, not only does its hull sink, but the increase in forward or aft draft also causes trim. The flow has a complex change depending on the relative position between a vessel and the seabed, which results in a new hydrodynamic force acting on the hull. Accordingly, inaccurate steering directions and times are very likely to cause serious accidents, like grounding and collisions. This is a critical issue in steering a vessel. Marine accidents involving very large vessels have a large scale and require enormous repair costs, which may cause a great loss to the ship owner and operator. Moreover, such an accident can lead to marine pollution accidents, such as oil spills over a large area.
Barrass (2015) defines the squat in shallow water as "The overall decrease in the static underkeel clearance, forward or aft, is called ship squat. It is not the difference between the draughts when stationary and draughts when the ship is moving ahead". It is also stated that such a phenomenon consists of sinkage and trim.