Under performing winch,Cable does matter

Submitted: Tuesday, Jul 26, 2005 at 00:28
ThreadID: 25056 Views:2299 Replies:6 FollowUps:10
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Tried Using My winch a few weeks back with a 10m pull and no dice. I have since aquired a snatch block which allows me to run out much more cable (I have 50m of cable) So I tested it again with a short pull and found it had the grunt to tow my 4by along with all 4 wheels locked up in low 4 1st, Until it got to 5m (10m of line pull) proving to me that the less line on the drum the better the pull
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Reply By: Kiwi Ray - Tuesday, Jul 26, 2005 at 06:56

Tuesday, Jul 26, 2005 at 06:56
Hi Davoe
That rated line pull on a winch is on the first layer of the drum and as it fills up the line pull drops off real quick. Just a rough guide a 9000 lb winch when full will only pull about 2500 lb.
Ray
AnswerID: 122051

Reply By: G-wizz - Tuesday, Jul 26, 2005 at 07:55

Tuesday, Jul 26, 2005 at 07:55
You do know that the snatch block is a pulley and that it reduces the load on the winch don't you? A snatch block can actually double the pulling power of a winch if used correctly.
AnswerID: 122058

Follow Up By: F4Phantom - Tuesday, Jul 26, 2005 at 10:23

Tuesday, Jul 26, 2005 at 10:23
if you use a snatch block you will get double the power from the winch and the winch cable will be under half the tension. thats if the block is running the cable approx 180 degrees.
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Follow Up By: Member - Davoe (Widgiemooltha) - Tuesday, Jul 26, 2005 at 11:04

Tuesday, Jul 26, 2005 at 11:04
yea know that although I cant wotk out the physics involved. interestingly it still stalled out about 5m from the tree. In a real situation I would be better off selecting a tree about 20m away giving me 40m of cable out and working on the bottom layers of the winch
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Follow Up By: F4Phantom - Tuesday, Jul 26, 2005 at 15:57

Tuesday, Jul 26, 2005 at 15:57
The physics is as follows as you may have already guessed.

the snatch block is a pulley. If you use the normal winch speed you have normal power and normal speed, if you half the winch speed via pulley you double the power and half the amount of tension on the cable. It is a fairly simple calculation of power vs speed and even easier than acceleration calculations which include rate of change becuase the winch is linear. The amazing thing about all this to me is the halving of tension on the cable, my dynamics teacher went over that point with me several times cause i just wouldnt believe it, but apparently it is true, so good news if you want to ease the wear and tear on expensive equipment.
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Follow Up By: Member - Davoe (Widgiemooltha) - Tuesday, Jul 26, 2005 at 16:10

Tuesday, Jul 26, 2005 at 16:10
I am sure your explanation is correct but you have confirmed to me why i dont understand the physics, Still its like alot of things I dont have to know how they work - just how to use em, great for dumb people like me:)
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Follow Up By: Member - Tonester (VIC) - Thursday, Jul 28, 2005 at 13:50

Thursday, Jul 28, 2005 at 13:50
Davoe, consider hanging from a branch with your two hands. Pretty easy right. Try and let go with one hand and hang on - it feels twice as heavy. Nothing to do with speed, its just that two cables pulling wieght share it b/w them (eg. half each), instead of a single cable handling load. Ever done a sheep shank on a rope to tie something off? Same principle applies.
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Reply By: AT4WD ADVENTURES - Tuesday, Jul 26, 2005 at 13:23

Tuesday, Jul 26, 2005 at 13:23
Davoe,

Even better still hook up two snatch blocks to lessen the effort again on all equipment. Cables runs from winch to first block mounted off pull point back to car snatch block then back to pull point. Enable more cable to be spooled off winch in a short distance. Slower, stronger pull but less effort on equipment.

IMHO I would not use a winch without a snatch block in any case as the single line pulls with off the shelf unmodified winches exerts substantial stress on the equipment after the rated layer is filled.

My two bobs anyway.

Stuart
AnswerID: 122114

Follow Up By: Member - Davoe (Widgiemooltha) - Tuesday, Jul 26, 2005 at 16:15

Tuesday, Jul 26, 2005 at 16:15
hear ya but in most of the winch pulls i have done are on salt lakes where doubling back isnt an option and extension straps are needed. My last atempt at winching could have benifited from what you speak of but in the end prob the highlift and reversing back were prob the best solution. Like any recovery it is a matter of assesing the situation and seeing what you have then (hopefully) picking the right option
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Follow Up By: F4Phantom - Tuesday, Jul 26, 2005 at 17:32

Tuesday, Jul 26, 2005 at 17:32
what kind of salt lakes mate? i once saw a few driving from kalgoorlie to esperance, i walked up to one and broke the salt surface, underneath was the stickiest and STINKIEST mud ever. The smell would not leave my shoe and really made me feel sick, driving through that would be utter madness and you would be bogged within 1 meter of salt.
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Follow Up By: Member - Davoe (Widgiemooltha) - Thursday, Jul 28, 2005 at 12:14

Thursday, Jul 28, 2005 at 12:14
Not ones that bad F4 we were wrrking large areas in dense bush SE of Norseman Most of the areas we wanted to check out were around saltlakes. The saltlakes in the area are often long and thin and we would attempt to drive the sandy beaches as a better option to straight bush bashing. at times it was best to skirt the edges of the lakes (Never accross that is just suicide) most of the time the edges were firm but every now and again we had to make use of vegetation along the lake edge for winch recovery
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Reply By: Outnabout David (SA) - Tuesday, Jul 26, 2005 at 13:41

Tuesday, Jul 26, 2005 at 13:41
Should always select a mountint point that allows full use of all cable on the drum. Winching with many layers on the drum increases considerably damage and jamming of the cable as it pulls down between spooled cable.
AnswerID: 122119

Follow Up By: Member - Davoe (Widgiemooltha) - Tuesday, Jul 26, 2005 at 16:18

Tuesday, Jul 26, 2005 at 16:18
Was the first time I had been bogged with a close mounting point and coupled with 50m of winch cable around 2wice what I was used to was what led to the initial problem. You are of course correct (as I found out) cable should be run out to a further point or probably even better run back and forwards (if close enough) through snatch blocks
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Reply By: Bonz (Vic) - Tuesday, Jul 26, 2005 at 18:08

Tuesday, Jul 26, 2005 at 18:08
I would have thought the winch would pull fine at 10 metres, even the lower pull power would still be significant, maybe you got a problem with yours that needs someone to take a look. Is it a high mount or low mount winch? Saw amazing high mount winches with two 24v motors at the Ateco last weekend.
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AnswerID: 122158

Follow Up By: Member - Collyn R (WA) - Wednesday, Jul 27, 2005 at 11:18

Wednesday, Jul 27, 2005 at 11:18
Make sure the winch cable is of adequate size.

Check it like this:

Length of conductor (in metres) X maximum current (in amps) X 0.017.

Example: 4 X (say) 300 x 0.017 = 20.4

Dividing this by an acceptable voltage drop of (say) 0.3 volts gives the approx cable size (in sq mm). Here the closest is about 60 sq mm (00 gauge - somertime shown as 2/0).

As heavy copper costs a motza, few winches are adequately cabled.

Note that winch power falls off at a rate proportional to the square of voltage drop, as well as increasing drum diameter.

In above formula length is conductor length - if there is a negative return cable that length too must be included.
Trust this helps
Collyn Rivers
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FollowupID: 377443

Reply By: robak (QLD) - Thursday, Jul 28, 2005 at 15:09

Thursday, Jul 28, 2005 at 15:09
Davoe

Your winch probably has a torque of around 2000Nm. Which means, that if the radius of the drum was 1 metre, then the pull would be 2000 Newtons (around 200 kg's)

However the radius of your actual drum is probably about 5cm (0.05 metres)
So...
2000Nm / 0.05m = 40 000N (which is about 4 000 kg's or about 9 000lbs)

As you wind the wire onto the drum, the radius of the drum increases. So, after winding for a bit, the radius increases to 10cm (0.10m)
2000Nm / 0.10m = 20 000N (which is about 2 000kg's or about 4 500lbs)

Therefore, the winch has it's greatest pull at the begining, and dies towards the end.

Just like car tyres. Larger tyres will give you less "power"

Hope tha clears it up somewhat.

R.
AnswerID: 122555

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