Nobody mentioned the weakest link when increasing MA. This is probably how you attach the FB to the line. Cammed ascenders are useful, but not all equal. Some are designed to slip at certain loads, rather than sever the line. Outside of this, a typical rope grab may sever the line @ 800Kg. A toothed ascender, at alot less! A VT probably would break the line at 50% of the lines rated strength; nothing to worry about with a safety factor of 10 on the line. I use a free sliding cam (not like a sprung Gibbs), so it can stay on the line when lowering. After I've finished pulling, I just unclip the FB from the cam and leave everything in its place. Very quick and smooth. my FB are rated at 600Kg, and have very efficient bearings. That means with one person pulling, I can't load the cam enough to cause the line to fail.
If I was going to need more MA, I'd probably switch to a VT.
More MA than that, and I'd make sure the FB were added externally to another MA system, which is probably what Mark and Mahk were doing, I'm not sure.
Placing MA on the FB via a truck winch can be catastrophic. You'll get potentially 5 x the winches pull, which would probably cause the cam to sever the line, or the FB to fail!
I always set up the FB horizontal at waist height where possible, and clip a handled ascender to the pull length for maximum power on the pull. Only one person pulling with my set up.
Definetly don't expose them to shock loads - I had one bust on me when a big tree it was supporting rolled slightly - it shot up the line at me like a rocket. It was a very dramatic commando roll with the c/saw to get out of the trees way, as the missile shot over my head!
I attach them to the cam and Portawrap with 50kN steel HMS krabs. They're big enough to clip both and still be loaded correctly. 600Kg x safety factor of 5 for hardwear = Break strength of 3000Kg (not exactly 30kN). So these krabs are stronger than they need to be, but I use them for different duties. Krabs will take a proof load of 50% of the break strength, but its better to run them at 5:1 safety factor, to account for other variables and guaratee safety (we're never quite sure how much load is on the line to run things so close). Locking gates mean you can use them elsewhere without worry.
They're a great tool - have fun!
