Waterline

The waterline is the line around a vessel’s hull where the surface of the water meets the boat when it is afloat. It moves with loading, trim, fuel, water, crew, and sea conditions, and is the reference point for measuring how much hull is immersed versus exposed.

For boaters, the waterline is a quick visual check on safety and performance. A lower-than-normal waterline can indicate excess load or water ingress, affecting Draught, stability, speed, and fuel use. It also helps judge Freeboard and understand changes in Displacement before entering shallow water, loading stores, or departing offshore.

Designers also use the loaded waterline to calculate Length water line, an important factor in hull speed and sailing performance. In PredictWind routing, accurate boat setup, loading assumptions, and performance data help produce more realistic speed estimates and passage plans.