Page 240 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition
P. 240

  9.2 TMS-based vehicle deployment techniques 229
As depicted in Figure 9.8, the fleet angle is described as the angle between the projected centerline
of the sheave and the cable launch point from the drum. It is important to spool the cable onto the drum
in a fashion that assures orderly lay of the cable onto the drum. For wire rope, that angle is normally
Ingersoll Rand, based on information from the Wire Rope Technical Board, states that to main- tain a proper fleet angle (1.5 for a smooth drum, 2 for a grooved drum), the distance from the lead sheave to the centerline of the drum (LDS) is:
LDS 5 half the drum width ðfeetÞ 3 38 for smooth drum; 29 for grooved drum
Accordingly, for a smooth drum 40 in. wide, LDS would be 1.66 ft 3 38 5 63 ft—obviously, a distance that is not preferred when mobilizing an ROV system. Therefore, to reduce the footprint of the spread and spool the cable onto the drum in an orderly fashion, a mechanical device known as a “level wind” guides the cable onto the drum to maintain a proper fleet angle. Also, in order to distribute the line pull evenly onto the drum (as opposed to focusing the pull at the line anchor point), several wraps of line are left on the drum (typically 10% of the line length, although it would be preferable to have enough line to provide a complete first layer on the drum) so that the line forces distribute over the drum more uniformly.
Winches are “load/lift-path” items requiring certification of the lifting system. Further, winches are not allowed to be in a free-spooling configuration. This requirement forces braking systems to be fail- safe with the braking system “failing” into a “braking on” mode should power be lost to the lift motor.
As shown in Figure 9.9, a winch system is composed of several basic components:
1. Winch base
2. Hydraulic motor and brake (or hand crank and manual brake)
3. Brake cylinder and motor support
4. Drum assembly
5. Level wind

between 0.5 and 1.5 . An excessive fleet angle bunches the cable onto the drum causing either exces- sive wear or uneven spooling, while too small a fleet angle causes any number of disorderly modes.
 Level wind
Supports
Brake and motor
Drum with cable
Base
    FIGURE 9.9
Winch components.
 











































































   238   239   240   241   242