On installations where the wire rope passes over a lead sheave then on to a drum, it is important that the lead sheave be located at a sufficient distance from the drum to maintain a small fleet angle at all times. The fleet angle is the side angle at which the rope approaches the sheave from the drum. It is the angle between the center line of the sheave and the wire rope.

Experience has proven that the best wire rope service is obtained when the maximum fleet angle is not more than 1 1/2 degrees for smooth drums and 2 degrees for grooved drums. The maximum angle is the angle between the center line of the sheave and the rope when it is at the end of its traverse travel on a drum. Fleet angles of 1 1/2 and 2 degrees are equivalents of approximately 38 and 29 feet, respectively, of lead for each foot of rope traverse travel either side of the center line of the sheave. Thus, a smooth drum with 3 feet traverse travel with the center of travel in line with the lead sheave should be located not less than 57 feet from the lead sheave. If the drum were grooved, then minimum distance would be approximately 43 1/2 feet.

Sited from: American Tiger Wire Rope Engineering Handbook, Page 66