The fleet angle is the angle between the line of the rope/cable and the axis of the drum or spool. It is measured from the point where the rope leaves the drum to where it enters the sheave or pulley.
The fleet angle is crucial because it affects how the rope or cable is wound onto the drum. An improper fleet angle can lead to issues like uneven spooling, excessive wear on the rope, and increased stress on the cable and drum components.
The fleet angle should typically be kept within a certain range to ensure smooth operation. For most applications, a maximum fleet angle of 1.5° is recommended. If the angle is too small (less than 0.5°), the cable may pile up unevenly on the drum. If the angle is too large (greater than 1.5°), the rope may rub excessively against the drum flanges, leading to wear and possible damage.
To control and maintain the proper fleet angle, devices such as level winders or fairleads can be applied to guide the rope or cable properly onto the drum.
Read here more about it and how you can calculate the fleet angle.