Question 63 GLI03 - Master-LT 500-1600 GRT

The Correct Answer is B **Why Option B ("The bow will squat farther than the stern") is correct:** When a large vessel, particularly one with a full form (like a tanker or bulk carrier), moves through shallow water at a significant speed, a phenomenon known as the "shallow water effect" or "squat" occurs. Squat is the reduction in under-keel clearance (the distance between the bottom of the ship and the seabed) due to hydrodynamic forces. As the ship pushes water forward and to the sides, the water level around the hull drops, lowering the entire ship. For full-form vessels operating in shallow water, the wave system generated by the ship causes a pressure differential: * **Positive Pressure:** builds up near the bow. * **Negative Pressure:** is strongest toward the stern and amidships. However, when the vessel is moving fast, the water accelerates significantly around the hull, creating a large area of low pressure that pulls the vessel down. Due to the asymmetric pressure distribution and the way water flows past the bulbous bow (if present) and the full body of the ship, the trimming moment usually causes the vessel to change trim **by the bow**. This means the reduction in draft at the bow (the **bow squat**) is greater than the reduction in draft at the stern (the stern squat). Therefore, the bow will squat farther than the stern, increasing the forward draft. **Why the other options are incorrect:** * **A) The vessel's maneuverability will increase:** Incorrect. In shallow water, maneuverability is significantly degraded. The proximity of the bottom increases the effective mass of the water surrounding the hull, reducing rudder effectiveness and increasing the turning circle. High speed only exacerbates the instability caused by squat and hydrodynamic interaction. * **C) The vessel's speed will increase:** Incorrect. As a vessel enters shallow water, the resistance (drag) experienced by the hull increases drastically due to the restricted flow of water beneath and around the ship. This means that maintaining the same engine power will result in a **reduction** in speed. To maintain speed, significantly more power is required, but typically, speed is reduced to manage risk and control squat. * **D) The vessel will rise slightly, on a level plane:** Incorrect. The shallow water effect causes the vessel to experience **squat**, meaning the vessel is drawn down and the draft increases (under-keel clearance decreases). The vessel does not rise; it sinks (squats). Furthermore, it does not remain on a level plane; it experiences a change of trim, typically sinking farther by the bow (B).