Thread: Hand vs electric winch: solo travelling

Me doing a recovery after reading this thread...

Originally Posted by Tank

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.


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.

Frank, you werent wrong, Ive got books that prove exactly what you're claiming provided you restrict yourself to the sections about rigged to advantage and rigged to disadvantage, I know I promised to do some pictures and experiement and I still will if I can get my hands on the scale sets but in the short term, the disconnect here is in identifying rigged to advantage, rigged to disadvantage on a single sheeve ppully and assessing its MA.

you're also not wrong with the reduction for a sheve its not a fixed percentage and the formula for a Fiber cored 6 lay rope with a 3/16th strand and a 6x9 lay construction on a minimum 8d turn has an swl reduction factor of 50% AND has an initial hauling loss of 50% decreasing to 30%

short version of all of that? using easy numbers, if that wire rope could hold 2 T and you reeved it through a minimum diameter block to lift a 2 T weight you would initially have to apply 2T worth of pull on a pully that was rigged to advantage you might as well just hauled the thing up on a single line and if you tried to lift the load using that pully rigged to disadvantage you couldnt. step ouut to a 15D pully and youre at 20% ste out to something like 40D a your back at 5%.

for those paying attention no you wouldnt use that construction rope as a winching rope, its a static line grade rope. think bridge stay not hauling line

Originally Posted by roverrescue

Frank.
First I don't want to bust your head. Honestly I just want the principles of physics to be seen. I don't discount your knowledge or experience but you are just wrong on this.

In the example I gave of a winch a crane a 1tonne mass and a block do you or do you not agree in the 2:1 MA. If so then the fact is that relatively speaking it is irrelevant if the load is moving or the crane is moving.

I think Dave needs to do some load testing using inline scales. Hell I was looking and can buy some PRC magic scales rated to 300kg that will do to prove this beyond reasonable doubt....

Dave if you can't I will just say the word.

S

I was hping to get the strain gauges from work to do it sometime next week when I do a function test and service on dads winch. I cant afford to do it full scale but I might be able to get some 5 kg fish scales and lego it.

the laptop OS build is on hour 4 of one so far so the pictures arent going to hapen tonight so hopefully over the weekend....

Originally Posted by Landi

Me doing a recovery after reading this thread...

nahh, this is the easy stuff...

wait till you see the math on some of the really advanced stuff, multiple winches pulling into different parts of a compound setup an the dynamics of the load in motion change the formulas part way through because the pull angles change...

This was what I was taught at school/uni (im a practicing structural engineer, if that makes any difference to the value of my opinion)

"The tension in the wire/rope is the same at all points along the rope (disregarding friction)"


pic link: https://www.dropbox.com/s/0gic152376...7.jpg'dl=0

In attached pic, situation A has one pulley but only 1 line of rope is supporting the weight (of say 100kg). Therefore the tension in the line is 100kg (or 1kN)

In situation B (similar to a winching 4wd) there is one pulley however there are two lines to the weight. In order to maintain equilibrium the tension in the line = 50kg (0.5kN). Increase the tension at the point of the arrow (ie by using a winch attached to the weight) past 50kg and the weight will move towards the top pulley.

In situation C there are two pulleys though the rope is anchored to a third point (similar to situation A). As there are two ropes fixed to the weight, the tension in the rope is 50kg (0.5kN). Increase this tension past 50kg by pulling on the rope and the weight will lift.

Disregarding the angles of the rope (please don't go there - this is just a diagram) the force in the top pulley equals the weight (100kg) in all situations. However in B and C the tension in the rope is only 50kg. My understanding is that is a mechanical advantage of 2.

Cheers

Dan

Ps. Sorry for the lousy photo link. I don't have photobucket or anything at the moment and don't have time to set one up!

Whoops.

Correction: the load on the pulley in case A is 2W, and the load on the top pulley in case C is 1.5W. (Once again ignoring angles)

Cheers

Dan

So Landi, all clear now
Buy a HP calculator to run the numbers , then call Land Rover Assist

Originally Posted by AndyG

So Landi, all clear now
Buy a HP calculator to run the numbers , then call Land Rover Assist

close..
use the calculator app on your phone and then use the phone to call landrover assist.


of course if you're as lucky as I am when it comes to this stuff the battery will go flat in the phone so you'll have to do all the math from memory using a stick and the dirt on the ground then rig it all up do the recovery, pack it all up and then drive back to the campsite to grab the phone charger out of the goddies bag.

I have never had a winch on a vehicle and probably never will.

I have nearly always carried a 3t come-along with a 3-5mtr chain.

I also have never used it in anger but have exercised recovery just to practise.

It is the simplest thing to use, does not tire you out using it or carrying it (you can get them in aluminium).

You set it up wherever and to whatever your task is.

And on your own , incorporating your snatch strap , you can load the come-along right up . get in your vehicle and assist your recovery under the snatch strap tension.

When it goes slack just load it up again.

It works and doesn't have to go into the mud if you're in mud because you can set the come-along up wherever you want.

My favourite.....unfortunately now I will have to buy one because I'm retired and the big store in the sky is now closed to me.

When I first got my land rover i I was a believer that winches weren't necessary, I thought they were only for posing & decoration etc. I few long walks to the top of a high hill where my phone would work cured me of that delusion. . I started to think maybe there's a reason 50% of the 4x4 s have winches.

And I was amazed at how easy it is to stop a Land Rover, ( no prior experience) in muddy & hilly terrain, one front wheel slipping and one back wheel slipping & you're stopped. It's surprising land rover didn't use limited slip diffs or true tracks fitted to the car from the factory, I think toyota and nissan offered LSD in the back for that reason. Once I parked on a gentle grassy slope and could not proceed .

Fortunately there was a lot of good trees where I drove so a winch was on obvious addition, and not too expensive about $1000 for an unused 2nd hand Warn 9000. ( about the cost of set of good mud tires at the time)
It made bush driving more relaxing and gave some confidence i could take car of myself, if i got bogged.

But it didn't address the key issue of why I was getting stuck; 2 open differentials. I fitted the maxi drive myself, but if was fitted professionally it was 3 times the cost of the winch. I still got stuck but no where near as often, so the winching was reduced. To those who never need a winch I salute you , dammed skillful driving and good vehicle preparation.

cheers simmo