hullwater

Hullwater is a term occasionally used in nautical contexts to denote the water immediately surrounding and contacting a ship's hull as it moves through water. It is not a standard technical term in modern naval architecture; more precise phrases such as boundary layer, hull wake, or hull-flow are commonly used to describe the same phenomena.

In practice, hullwater refers to the viscous region of the flow in contact with the hull. This region is characterized by a boundary layer that adheres to the hull surface and transitions from laminar to turbulent as speed increases. The geometry of the hull, speed, water temperature, and salinity influence the thickness and behavior of the hullwater, which in turn affects viscous drag and overall propulsion efficiency.

Studying hullwater is important for predicting drag, selecting hull coatings, and improving performance. It is investigated using experimental methods such as tow-tank tests and wave tanks and through computational fluid dynamics, which model the flow near the hull and in the wake. Designers aim to minimize adverse hullwater effects by optimizing hull form and surface roughness.

The term hullwater is somewhat informal; in technical writing, authors typically refer to the boundary layer near the hull, the hull's wake, or the viscous flow around the hull. See also boundary layer, hull wake, hull form, drag, and fouling.