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

Achieved speed (kt)

Required number in kt.

Target speed (kt)

Required number in kt.

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

Compare the achieved boat speed against the polar target speed as a percentage of target performance. Inputs are interpreted exactly in the displayed units and the calculation returns the following fields without presentation rounding.

Polar performance (%)

Returned number in %.

• 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.

• Polar Target Speed Calculator

  Compute the polar target boat speed by multiplying true wind speed by an efficiency ratio.

• Downwind VMG Calculator

  Compute downwind velocity made good as target boat speed times the absolute cosine of the true wind angle.

• Upwind VMG Calculator

  Compute upwind velocity made good as target boat speed times the cosine of the true wind angle.