Use of a rope grab to extend line on light weight winch

[Alan Smith]

I've recently added a radio controlled hydraulic winch to the crane on my 2 ton timber trailer. I'm finding it very handy to bring up timber to load onto the trailer.  I want to take advantage of the radio control for working at the far end of the line by extending the line via snatch block(s)  The winch cable is 25m of 1/4" steel rope which I don't want to run through blocks with ally sheaves so want to use my 10mm winch rope. At the moment I'm just tying a bowline on the bight at an appropriate point to hook onto the steel winch cable but I was wondering if a rope grab might be a more convenient way to achieve what I want. I know it's not what they are designed for. Or perhaps someone might know of a better solution.

[peds]

Problem with using a bight that you've clipped into is it weakens the rope and provides a possible point of failure. That point of failure is probably still wildly outside the forces you are working with, but still. A rope grab is exactly what you want in this situation, or even a prusik, as long as it's made with decent strong cord, if you use cord with 20kN breaking strength then it definitely won't be the weak point in your system.

The good thing about rope grabs and prusiks is that they start to slip on the rope a looong time before the forces get high enough to cause catastrophic failure, which is actually a good thing. Where prusiks have a slight edge over rope grabs, other than the cost, is that they bite the rope again sooner once the forces are lowered. Double check the numbers, but these things generally all break around 20kN, grabs or prusiks start slipping somewhere between 8 and 11kN, then grabs grab again at about 4kN, but prusiks prus at around 6 or 7. These are figures from memory, don't quote me, I'll try and remember more exact ones at some point.

 

That bowline on a bight won't slip at all, it'll hold on until something breaks, giving you no opportunity to identify snags in your system before it explodes.