The bearing from a sailing craft's current location to a destination or racing mark that lies within the no-sail zone, may lie on one side or other of being directly upwind. The tack on that side is "favored", because the destination lies closest to the craft's highest point of sail—its "best course" is close-hauled on that tack. Wind shifts that improve the angle towards the destination are called "lifts"; those that increase the angle away from the destination are called "headers". A sufficiently large wind shift may cause the destination to lie on the opposite side of the direction from which the destination or mark lies and indicate a tack to the favored side—tacking on a header. Apparent wind sailing High-performance sailing craft, such as sailing catamarans, sailing hydrofoils, ice boats and land-sailing craft, may be capable of speeds exceeding the true wind speed, sailing off the wind. Because the speed of the craft is a dominant contributor to the apparent wind, the apparent wind angle shifts forward. Such sailing craft may tack, while going downwind, under the principle of apparent wind sailing. Racing Sailing race courses may be triangular, windward-leeward triangular, or simply windward-leeward, each of which involves at least one leg directly to windward. The windward mark may favor a best course on a given tack, until the wind shifts significantly. Wind strength and the relative position of other sailing craft may determine how frequently to tack. Tactics A boat to windward of others enjoys undisturbed air, while disturbing the air for nearby boats that are downwind and behind. To keep this advantage the lead boat will often try to "cover" the trailing boat(s) by maneuvering to keep them "blanketed" in the disturbed air coming from its sails. The trailing boats seek to avoid the disturbed air from boats to windward without losing too much speed or momentum. A "tacking duel" develops when a leading boat decides to cover a trailing boat and the trailing boat seeks to escape the disturbed air. A successful approach for the trailing boat is to tack within the area of maximally disturbed air, where the wind has the least effect on the boat's wind-caused drag (windage). Roll tacking Roll tacking, usually while racing sailing dinghies, involves aggressive heeling of the sailboat, as the skipper and crew move towards the windward side during the first half of the tack when the boat crosses