Thread: Hand vs electric winch: solo travelling

Page 25 of the Rigger's Guide that I linked to back in post #39 has more detail about the issues Frank has covered regarding the use of pulleys with wire ropes.

Tank if you had a stuck vehicle and some trees and blocks available and wanted to get max MA how would you set it up? A diagram would be great because I have trouble visualising this stuff.

Cheers

Yeh agreed. A diagram would be great. Even university physics isn't helping me in understanding this one...I can definitely understand using a tree further away to un-layer more of the rope, but let's say there's only 1 suitable tree to use, 10-15m away, surely it would be better to use a snatch block at the tree, running it back to a recovery point on the front. Assuming of course you're using suitable and appropriate gear. Correct diameter snatch block, rope, rated shackles etc

Tank
First I completely agree that by running out cable to the first layer is a great way to increase pulling capacity. My winch only has 20m of dyneema on it but I carry lots of 50m lengths of extra dyneema to get length. This means the winch is generally always on lower wraps of the drum improving pulling power.

But now getting onto your rigging of winching riddle me this.

-Take a nice gantry crane with an winch rated to SWL 2T
-Take a cable down from a crane, to a 1T mass sitting on the floor and winch it up. Lets say the mass moves upwards at 1metre per second.
-Now place a block on the 1Tonne mass, send the hook through the block and back up to the crane and winch. Assuming it is a non load dependent constant speed hydraulic motor, how fast will the mass move upwards?

Obviously because the block is on the moving component you have your 2:1 MA which results in the mass moving 0.5m for every 1m of winching and as such the mass moves upwards at 0.5metres per second. And excluding friction etc etc you could say the load on the crane is halved due to the MA.

Now relativity is a bitch...

Have a read of this thread
MA debate and snatch blocks - Page 2 - Pajero 4WD Club of Victoria Public Forum

Mr Pajero did a winching experiment (using the well worn method of attaching the hook end to the vehicle) and found that winching 1m of rope equates to 0.5m of movement... Relatively speaking no different to the crane situation and as such there IS a MA when the cable is attached back to the bogged vehicle. The relative movement of the crane or the mass is irrelevant, it is that the load on the two cables is shared compared with a single cable.

If you disagree please explain how the pajero only moved 0.5m for 1m of winching?
If there is indeed no MA as you profess the pajero would have to move a metre for each metre of rope winching.

Peace

Steve

Sorry steve...you're very close but have made the same fopar in your descrpition as what Tank is making... but I know exactly what you mean and presume it was an expressive error. your original is in blue my corretion is in red, apologies for cutting the post down.

Originally Posted by roverrescue

Tank

But now getting onto your rigging of winching riddle me this.

-Take a nice gantry crane with an winch rated to SWL 2T
-Take a cable down from a crane, to a 1T mass sitting on the floor and winch it up. Lets say the mass moves upwards at 1metre per second.
-Now place a block on the 1Tonne mass, send the hook through the block and back up to the crane and winch. Assuming it is a non load dependent constant speed hydraulic motor, how fast will the mass move upwards?

Obviously because the block is on the moving component you have your 2:1 MA which results in the mass moving 0.5m for every 1m of winching and as such the mass moves upwards at 0.5metres per second. And excluding friction etc etc you could say the load on the crane winch is halved due to the MA.

the total load on the whole of the crane is still 1T but the load on the winch is now halved, the other half of the load is born on the body of the crane from teh point where you have the cble anchore

Tanks been taught on the old school ways where you basically never do what you've just described because the winching limit is also the anchoring limit for that point so to gain additional lifting ability you need to incorporate a second anchor point.

unless hes also done plenty of shipping work he'll also be working off of the base that the winch is not able to move (closer to the load), the load must always come to the winch.

we had an instructor on one of my crane courses who had the same problem, 2:! hanging from a head of a crane works because the block is moving, 2:1 on the ground cant because the block is stationary. me personally I blame the following phrase.

"if the heaving line is coming from the moving pully the system is rigged to advantage, if it is coming from a stationary pully it is rigged to disadvantage"


as I'm about to get my replacement computer onlineif all goes well I'll do some drawings tonight I'm also due to do a service on a winch so I might even be able to demo and strain gauge some of the configurations..

yeah good point I wasn't clear in my wording (AND this topic does need to be accurately worded)
Your red is totally correct load on the crane is unchanged but load on the winch is halved.

As you state in the second scenario the load is half to the winch and half to the attachment on the crane - overall though the load(force) on the crane is a function of 1000kg x 9.9m/s/s.

s

First up, I thank you all for not threatening to kill me, like those clowns on that other Forum, if you don't agree with what I've written.
I used to be a permitted rigger, (under instruction) till I got the riggers job in the Boiler Shop and Turbine shop on Cockatoo Island in Sydney harbour, after working a number of years in the mining construction business all over Australia.
Now I thought I knew it all and wasn't pleased when Vickers Cockatoo asked me to do a 12 months TAFE course, because they had no ticketed riggers on the island and permitted riggers need to work under a Ticketed rigger.
So the first thing I learnt was that there was a whole lot of maths involved.
The first day at TAFE was a Maths exam, out of the 150 or so would be riggers only around 50 passed the Maths exam and went on to do the riggers course.
The course opened my eyes and mind to parts of rigging that I would never had known except by Accident, it IS a very dangerous business esp. with just a little knowledge.
I haven't worked as a rigger (except when 4WD recovering) for 30+ years and I do not profess to know or remember it all, as you may or may not have noticed I have wrongly claimed that friction on each wheel when using snatch block/s was up to 20% of the load, in fact it is 5%, so sorry there.
I would love to be able to illustrate with drawings different ways to set up cables, blocks, straps and other ways to extricate yourself from a bog or whatever, but I have no idea of how to get a drawing onto the forum, I have enough trouble with photos, Maybe Allan can come around and educate me, never to old to learn and he is a teacher.
There is a hell of a lot of writing to explain why certain things happen like winch a metre of cable thru a block and the vehicle only moves 1/2 a metre, to do with pulling to advantage or disadvantage, as I am a single finger typist it takes me forever to get my point across, maybe I'll write a booklet.
The simple explanation for MA using pulleys is to rig a pulley up to a rafter in your shed/whatever put a length of rope though and tie a bucket to each end and place an identical weight in each one, say a house brick.
You will find, of course that they balance each side out, which means if you have 10 kilos on each side you have you have 20kilos on the rope holding up the pulley. To move say the left side bucket up you will have to place more weight on the other bucket to overcome the friction generated in the pulley which can be up to 5%/pulley so you need to add that 5% to load on the rope holding the pulley, this equates to a MA of 1.
Do the same thing to yourself, make a loop in one end of the rope, sit your bum in it, your body is the load, your arms are the winch, with out using any other part of your body pull yourself up to the pulley, should be easy if you weigh 100ks. you will only have to apply 50ks. + 5% friction, if the pulley is giving you a MA of 2 as some are claiming, it has taken me over an hour to type this, so I'm taking a break for now, Regards Frank.

Originally Posted by roverrescue

yeah good point I wasn't clear in my wording (AND this topic does need to be accurately worded)
Your red is totally correct load on the crane is unchanged but load on the winch is halved.

As you state in the second scenario the load is half to the winch and half to the attachment on the crane - overall though the load(force) on the crane is a function of 1000kg x 9.9m/s/s.

s

Frank,

It's the shared knowledge that has accumulated in this place from those like you willing to share your knowledge and experience that makes this such a great place.

For sure not everyone will agree with everything... but the smart ones can spot those that know what they are on about.

Thanks for taking the time to help those that want to learn...