VMG Calculation

VMG calculation takes boat speed and the angle between the heading and the target bearing, then returns the made-good speed toward the wind or mark as speed times the cosine of that angle. Race navigators read the optimum upwind and downwind angles off the boat’s polar, where the VMG peaks; sailing higher or lower than that angle gives up made-good distance even if the displayed boat speed looks attractive. The same arithmetic drives the layline and tacking-angle outputs of onboard tactical instruments.