Drum Rotation and Rope Orientation
When you purchase your ComeUp Automotive or Powersports Winch, the rope will be installed in such a way that the rope winds on and off from the bottom of the drum spool (see Figure 1). This configuration is referred to as underwound. Operating the winch with the rope coming off the top of the drum (overwound) is discouraged for three reasons.
- If the winch tries to pull a load with the rope in the overwound orientation, the tension forces in the mounting hardware increase dramatically. This is especially true for the larger capacity winches such as the DV-12 or DV-15. When a load is applied to the winch rope, the winch wants to rotate about the front corners of the drum support castings. The mounting feet in the castings and the mounting bolts resist this rotation. When the tension in the rope is down low coming off the bottom of the drum, the forces that could “spin” the winch off of its mount are minimized. If the winch tries to pull a load when the rope is coming off the top of the drum, the vertical distance between the load on the rope and the mounting is greater which puts a larger strain on the castings and mounting bolts. The phenomenon is known as a “moment” which consists of a force at a particular distance. If the distance increases, the moment increases. Large ComeUp winches use a larger diameter drum so the distance between the bottom of the drum and the top of the drum increases by at least the sum of the diameter of the drum and the diameter of the rope. In the case of the DV-12, the forces on the rearmost mounting hardware would increase 2.7 times. See example at the end of this article. Additional layers of rope around the drum make the condition worse.In the overwound orientation, it’s possible to exceed the strength of the castings and/or the mounting bolts which could cause a failure resulting in the winch to launch off of its mount, potentially causing property damage, severe injury or death. See Figures 2 and 3 for correct and incorrect installations.
- If the rope comes off the drum from the top of the winch, the rotation of the drum will be reversed (rope in becomes rope out and vice-versa). In addition to possibly running the winch the wrong way, the cone brake system will not behave as it was designed. See Figure 3. The brake could fully lock up and with a load on the rope, you might not be able to unlock the brake by operating the winch. The brake actuating cam will operate in the wrong direction resulting in significantly higher amp draw and/or overheating the brake and motor.
- Depending upon your mounting kit, rope coming off the top of the winch drum could cause misalignment to the fairlead or slot opening in the mount causing undue strain on the rope against the fairlead or damaging the rope against the edge of the opening.
For these reasons, operating your winch in the overwound orientation could void any warranty and present a very dangerous situation.
If your mount system has a front supporting rail or other structural member which provides sufficient strength to support the winch on the pulling side of the winch, it may also be acceptable to mount the winch in an overwound orientation. Figure 4 shows the proper rope direction, looking at the winch motor end. The “L” shaped feature represents a solid support which must be part of the entire mounting structure. Figure 5 shows an improper orientation where the drum will rotate in the wrong direction as described in #2 above.
A DV-12 winch, mounted with feet downward, using the standard (4) bolt 4-1/2 by 10-inch pattern, with 12,000 pound rated load applied to the rope when it was near one of the drum flanges and on the first layer against the bare drum:
- In the underwound position, the rear mounting bolt nearest the rope exit point would see a tensile load of approximately 4,200 pounds.
- In the overwound position, the same bolt would see a tensile load greater than 11,000 pounds.