WIRE ROPES FLEET ANGLE
Fleet Angle for Wire Ropes: Best Practices for Safe Use
CRANE ROPES
THE FLEET ANGLE
The fleet angle (β) describes the lateral deflection of a rope on the drum or, in the reeving system, the deflection that a rope experiences, which spools from a fixed sheave from one edge of a drum to the other. Here it must be taken into account that the fleet angle for a typical arrangement with the sheave central to the drum naturally has its maximum at the drum edges. In addition the rope grooves on the drum itself also describe an angle, the so-called pitch angle (α), that must be subtracted from the fleet angle (β) or added to
it.
CAUTION
Generally the rope fleet angle causes the rope to not wind to its lowest point but instead the sheave first touches an edge and then rolls into the bottom of the groove. This so-called “forced torsion of the rope” increases with the fleet angle. The authoritative ISO standard 16625 limits the fleet angle to 4° for non-rotation-resistant ropes and 2° for rotation-resistant and low rotation ropes. This narrow restriction for low rotation and rotation-resistant ropes results from the fact that ropes with steel cores closed in the
opposite direction respond more sensitively to forced torsion than conventional ones. Lateral deflection can of course arise during rope installation. Here, the specified maximum fleet angle from ISO 16625 must also be complied with to prevent twisting developing during rope installation. The fleet angle can be minimised by establishing as large a distance as possible between the reel and drum or head pulley sheave.
