Use this sailing calculation as a planning or educational cross-check for navigation, wind and current, rig loads, stability, anchoring, tides, visibility, performance, or recovery under explicitly stated conditions.

Transverse load (kg/m)

Transverse load per unit length of the stay.

Stay length (m)

Length of the forestay.

Tension (N)

Tension in the forestay.

Compute forestay sag with the parabolic approximation sagMeters = transverseLoadPerMeterKg * 9.80665 * stayLengthMeters^2 / (8 * tensionNewtons). The tool evaluates the supplied inputs together and returns the named outputs below; it does not infer omitted operating conditions or change the units shown.^[1]

Sag (m)

Midspan sag of the forestay.

• Actual conditions change with vessel design and loading, sea state, wind, current, tide datum, weather, chart accuracy, equipment, crew, regulations, and safety margins. Simplified formulas do not replace seamanship, approved stability data, or current navigation information.
• Use finite inputs in the displayed units and preserve more precision than the final presentation requires. Independently verify safety-critical, financial, compliance, or production decisions.

Cross-check official charts, tide and weather services, instrument data, vessel manuals, and collision regulations; maintain conservative margins and a safe alternative plan.

• 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.

• Bowsprit Compression Load

  Compute the ideal axial compression required to balance a forestay load at a specified angle to the deck.

• Froude Number Calculator

  Compute the Froude number using froudeNumber = speedMs / sqrt(9.80665 * lengthMeters).