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

Target boat speed (kt)

Required number in kt. Target boat speed from the polar at this wind angle.

True wind angle (deg)

Required number in deg. True wind angle off the bow between ninety and one hundred eighty degrees.

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

Compute downwind velocity made good as target boat speed times the absolute cosine of the true wind angle. Inputs are interpreted exactly in the displayed units and the calculation returns the following fields without presentation rounding.

Velocity made good (kt)

Returned number in kt. Component of boat speed made good directly downwind.

• 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.
• True wind angle must be at least 90.
• True wind angle must be no greater than 180.
• 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.

• Upwind VMG Calculator

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

• VMG to Leeward Calculator

  Compute velocity made good to leeward from boat speed and true wind angle on a run.

• VMG to Windward Calculator

  Compute velocity made good to windward from boat speed and true wind angle.