When water builds up between the head of the vessel and the bank, it is known as what?

The correct answer is bank cushion. This term refers to the phenomenon that occurs when water builds up between the vessel's bow (the front of the boat) and the bank (the shoreline or riverbank). When a boat operates in shallow water or close to the shore, the displacement of water creates a cushion effect, which can lead to increased resistance and challenges in maneuverability. Understanding this concept is crucial for operators, as it affects the handling of the vessel and overall navigation safety, particularly in narrow or shallow channels. Being aware of bank cushion helps operators anticipate potential issues and adjust their approach accordingly to maintain control of the vessel.

In contrast, the other terms do not accurately describe this specific situation. Bank suction, for example, refers to the pull that a vessel can experience towards the shore due to the water being drawn in as the boat moves forward. Bow wave describes the wave created at the front of the vessel as it moves through the water, while draft surge pertains to the change in water level around a vessel due to its movement and weight. Each of these terms relates to hydrodynamics but does not capture the concept of water building up between the vessel and the bank as effectively as bank cushion does.