Use this sailing calculation for planning or education when the vessel, units, reference directions, environmental conditions, and assumptions are explicitly known.

Hull speed (kt)

Required number in kt. Hull speed of the vessel.

The cited overview of Sailing supplies background for the terminology and domain context used by this tool.^[1]

Estimate a hull's waterline length in feet from its hull speed using waterlineLengthFeet = (speedKt / 1.34) ^ 2. Inputs are interpreted exactly in the displayed units and the calculation returns the following fields without presentation rounding.

Waterline length (ft)

Returned number in ft. Estimated waterline length of the hull.

• Vessel design and loading, sea state, wind, current, tide datum, weather, chart accuracy, equipment, crew, and safety margins can make real conditions differ from a simplified result.
• Use finite inputs in the displayed units, preserve source measurements and assumptions, and independently verify consequential decisions.

Cross-check current charts, tide and weather services, instrument data, vessel manuals, and applicable navigation rules, and retain a conservative alternative plan.

• Air Draft With Heel

  Estimate effective air draft while heeled using a simplified rotation about the lower rail. Actual clearance also depends on hull geometry, trim, waves, and the heel pivot.

• Chain Catenary Sag Calculator

  Estimate the catenary sag of anchor chain between two points from its weight per meter, span, and horizontal tension using a parabolic approximation.

• Leeway Angle Calculator

  Estimate leeway angle with the empirical relation leeway = K times heel divided by boat speed squared. Calibrate K for the hull, keel, and knot-based speed data in use.