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VMG DEFINED 

Velocity made good, or "VMG," in sailing and specifically yacht racing, is the component of a sailboat's velocity that is in the direction of your mark. The concept is useful because a sailboat often cannot, or should not, sail directly to a mark to reach it as quickly as possible. Sailboats cannot sail directly upwind. It is usually less than optimal and can be dangerous to sail directly downwind. Instead of sailing toward the mark, the helmsman chooses a point of sail that optimizes velocity made good.