Relative Velocity                        (UNSW) Why can a sailboat travel faster than the wind when it goes against it, but can’t travel faster than the wind when going with it? The answer is the concept of relative velocity versus actual velocity. When a sailboat is sailing downwind, it can’t go faster than the wind because the wind pushing the boat is the only force pushing the boat in that direction. As the velocity of the sailboat increases, the difference between the relative speeds of the boat to the wind decrease. As the difference decreases, the force pushing the sail forward decreases so that the boat can never mover faster than the wind behind it. However, when going upwind, since the boat is going in the opposite direction of the wind, the relative wind speed to the sail is increased. Since there is a larger magnitude of velocity of the airflow hitting the sail, the force the sail exerts on the air must be increased, so the re-action force of the air pushing against the sail is increased. Therefore, the faster the boat is moving in the opposite direction to the wind the greater the force is pushing it forward.(Wolfe)