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.

Apparent wind (kn)

Apparent wind speed.

Suggest backstay tension from backstayPercent = min(100, max(10, round(apparentWindKt * 4))). 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]

Backstay tension (%)

Recommended backstay tension as a percentage of range.

• 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.

• Cunningham Tension Guide

  Suggest cunningham tension from cunninghamPercent = min(100, max(0, round((apparentWindKt - 8) * 6))).

• Vang Tension Guide

  Suggest vang tension from vangPercent = min(100, max(10, round(windSpeedKt / maxWindKt * 100))) using the boat's maximum working wind.

• Jib Lead Angle Guide

  Suggest jib lead angle from leadAngleDegrees = min(25, max(5, round(apparentWindKt * 0.8))).