Forces of yachting Yachting involves many forces which are manipulated in different ways during races. Consider the picture on the right. Wind forces act on the boat propelling it forwards on the surface of the water. Drag forces act to impede the boat's motion through the water. Other forces include gravity pushing the boat downwards while the buoyant force of the water acts upward. Gravity acts on a body through a point known as the centre of gravity. An object is very stable if its centre of gravity is below the point of rotation. Why are the sailors hanging from the side of the boat? Not all the forces acting on the boat are obvious. Take, for example, the wind forces pushing on the sail, the result would be to flip the boat in the water, however, this does not happen. When you look beneath the water line you can see why. Ballast is used to lower the centre of gravity of a boat below the point of rotation. One of the functions of a keel is to house the ballast. This helps stabilise the boat from wind forces acting on the sail that would otherwise flip the boat in the water. 1) The boat does not sink. This indicates that the drag and propulsive forces are equal drag and propulsive forces are unbalanced force of gravity and the buoyant force of the water are balanced force of gravity and the buoyant force of the water are unbalanced 2) The heavier the ballast the easier it is to flip the boat harder it is to flip the boat faster the boat will travel greater the force of propulsion 3) Streamline is a word associated with minimising which force? wind forces drag forces gravity buoyant forces 4) During the 1983 America's Cup campaign Australia 2 won with a revolutionary new winged keel. This keel lifted the body of the boat out of the water more than conventional keels. This reduced drag increased wind forces reduced gravitational forces