Thread: Winch on a winch!

????? I haven't seen the results published in any journals yet!

this predated my AULRO time and apparently tests conducted by drunk soldiers are not considered to be scientifically sound.

Slunnie is right in both scenarios. Never ever forget that your winch is mounted to your vehicle, which most importantly moves.....

Originally Posted by cewilson

Slunnie is right in both scenarios. Never ever forget that your winch is mounted to your vehicle, which most importantly moves.....

It's like having two blocks, one at the tree and one on the vehicle. Because the winch is attached to the end of the cable (through the vehicle bull bar) it's like having a continuous loop of cable between the two blocks. The winch then becomes a machine which shortens the cable, and it doesn't matter where you put it, as long as it's attached to the cable by its drum and its anchor point, you always get a 2:1 advantage. The reason you get 2:1 with the winch on the vehicle is because the anchor point of the winch is also doing useful work in moving the vehicle.
Take the winch off the vehicle and anchor it to the ground alongside the vehicle and you lose your 2:1 advantage. In this setup all the block on the tree does is change the direction of pull. The anchor point of the winch can't do any useful work because it can't move.
It's important to realise that this IS a 2:1 advantage, because the pull on the cable that holds the block to the tree can rise to twice the force generated by the winch (ignoring friction). So you need to be sure that it can stand the load. With a straight pull without the block, the load is limited to the force generated by the winch.

Hooking one vehicle to another and vice-versa is also like having two cables and two blocks, but now you have two devices to shorten the cable, so it happens at the speed of a single winch pull, but with twice the force. If you prevent one vehicle from moving, then twice the force is applied to the second vehicle (assuming identical winches) so you'd better be sure that the bullbar is firmly attached or you might pull it off!

Coop

Originally Posted by C00P

................................................It 's important to realise that this IS a 2:1 advantage, because the pull on the cable that holds the block to the tree can rise to twice the force generated by the winch (ignoring friction). So you need to be sure that it can stand the load. With a straight pull without the block, the load is limited to the force generated by the winch. Coop

Yes, everything you have written is correct. In bold above is something that is very easily overlooked. It is one reason why tree protectors are rated around 12,000 Kg. But also easily overlooked is the rating of the bow shackle that you should use to connect the tree protector to the snatch block: it also should be rated at twice the pull rating of your winch.

Originally Posted by Old Farang

But also easily overlooked is the rating of the bow shackle that you should use to connect the tree protector to the snatch block: it also should be rated at twice the pull rating of your winch.

Yep, spot on, all the tackle at the block end needs to be uprated.

The one I had more trouble getting my head around is the situation where the two cables are joined end to end.
First, I asked what would happen if a single winch was attached to a solid (immoveable) object like, say, Ayers rock. You engage the winch and the cable tightens, and then stops. Say the winch can pull with 1000kg, but the bogged vehicle doesn't move. Assuming the cable attach point, and the cable and winch structure can stand the load, and the winch doesn't burn out, then all the energy going into the winch is converted to heat. In effect, Ayers rock is resisting the pull on the cable by pulling back the other way at 1000kg (and it could probably do a lot more!).
Now replace Ayers Rock with another vehicle, winch and cable, joined to the end of the first cable. Engage your winch, and all that will happen is that the cable on winch 2 will spool out as the cable on winch 1 winds in. Now engage winch 2 (which can also pull with 1000kg). It will take up the slack, and then pull back the other way with an increasing load until it reaches its maximum of 1000kg, just like Ayers rock. If the second vehicle can't move, then everything stalls, and both winches expend their energy as heat. No useful work is done.
Now assume that one vehicle starts moving before the winches reach max load. The tension is now less than 1000kg, so both winches can start winding in, and the rate of closure of the vehicles can potentially rise to twice the rate of closure of a single winch. But the pull on the cable is no more than what one winch can generate. So there is no advantage, except that you have a cable twice as long, and you can get the job done faster. The two winches will, in effect, see the same load (ignoring friction and other random effects like drum diameters and so forth) and each will wind in as fast as it normally would with that amount of load. So the job gets done faster, but you don't gain any extra pull this way.

Coop
PS Just to throw another spanner into your thinking, the fact that the job is getting done faster means you have more POWER in this setup, but you don't put any extra load on the equipment. Fascinating, isn't it?

This is the most infuriating thread ever!

Both the winch winch and particularly the snatch block debacle!

If snatch blocks were just witch craft then no one would sell them, no one would buy them, no one would use them and cranes would have to be a lot bigger!

my theory on winch to winch is that the winch on the vehicle not moving will have the added force of the winch being pulled in on the moveing vehicle.
so if winch on stopped cvehicle pulls a 2500kg car then it has a 2500kg force on it, excludeing friction, now if the car being pulled attaches its winch onto the the other cable and pulls in at 1000kg force then the car that is stopped would now have a 3500kg force on the winch.

some one must know a college proffesor who can work this out woith some clever maths.