Ship Squat & Channel Clearance Calculator
Harbor & channel navigation safety: Calculate Bernoulli ship squat sinkage, bow/stern trim shift, and net Under-Keel Clearance (UKC).
Vessel & Channel Dimensions
Squat & Under-Keel Clearance (UKC)
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Frequently Asked Questions
What hydrodynamic mechanism causes ship squat in shallow water?
When a ship moves through shallow or confined water, water displaced by the forward motion must squeeze through the restricted space beneath the hull and along the canal banks. According to the Bernoulli principle and continuity equation, this constricted flow accelerates, causing a local pressure drop under the hull. The loss of buoyancy force pulls the vessel downward (sinkage) and induces a pitch moment (trim).
Why does speed have such a dramatic impact on squat?
Squat scales roughly with the square of the ship speed through water (V_k^2.08). For example, doubling vessel speed from 6 knots to 12 knots causes squat sinkage to increase by more than fourfold (from ~0.35 m to >1.5 m), which has caused numerous canal groundings and bank collisions.
Why do full-form tankers squat by the bow while container ships squat by the stern?
Vessels with high block coefficients (C_B > 0.70) like VLCCs and bulk carriers have blunt, full bows that push massive water volumes ahead, inducing peak Bernoulli suction under the forward third of the hull (bow squat). Fine, slender vessels (C_B < 0.70) like container ships and frigates generate peak suction near the stern due to high aft run velocities and propeller suction (stern squat).