 | Home > Technical > Winching: theory vs real life |
 
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| leeds Member Since: 28 Dec 2009 Location: West Yorkshire Posts: 8582  
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Yes at a lower load the winch line will pull in faster. However when you double line to move one metre forward you have to take in two metres of line. Halving the load at decent winch loads does not necessarily mean double the line speed. Likewise halving the load does not mean halving the current drawn. The relationship between load, line speed, current draw,etc are not simple linear functions and will vary between winch brands/models and battery types etc. Double lining is a safer way of winching and as a simple broad brush explanation halving the load, halving the speed, doubling the time is a straightforward concept to get over. Also avoids discussion of frictional losses around pulleys, angle between the two sections of winch line, output of alternator, discharge characteristic of batteries etc etc Brendan |
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14th Jan 2015 10:53am |
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| zone30 Member Since: 07 Sep 2012 Location: Gent Posts: 669  
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Reading the specs for for instance Warrior winches I noticed:
Specs: +++ 9500 standard - 500 euro +++ 3000lbs - 3.8m/min - 170A 6000lbs - 3.0m/min - 260A 9500lbs - 1.9m/min - 380A 4m@6000lbs = 260*4/3 = 347 +++ 9500 HS - 535 euro +++ 4000lbs - 3.8m/min - 300A 6000lbs - 3.6m/min - 400A 9500lbs - 1.9m/min - 530A 4m@6000lbs = 400*4/3.6 = 444 +++ 12000 standard - 532 euro +++ 4000lbs - 4.0m/min - 220A (6000lbs - 3.4M/min - 280A => approximation by myself) 8000lbs - 3.0m/min - 330A 12000lbs - 1.8m/min - 450A 4m@6000lbs = 280*4/3.4 = 329 My opinion: the standard 9500 or 12000 is the best buy. The HS is overkill and wont give you enough extra. There's not much price difference. My conclusion: if you don't need the speed, go standard and slow. My next question then is: how "heavy" does a winch need to be? Would an 8000lbs not suffice? Why is 9500lbs seen as the entry level? |
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14th Jan 2015 1:10pm |
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| blackwolf Member Since: 03 Nov 2009 Location: South West England Posts: 17606 
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Don't forget though that doubling the line can also cause problems.
If you have something really immovable and you pull with a single line, the winch will stall at anything up to its max rated bare drum single line pull (8k to 12k depending on winch). If you have doubled the line back to the winch vehicle, and the winch still stalls, although the line tension is the same the load on all the strong points is doubled, greatly increasing the possibility of attachment points, bits of rigging, bumpers and crossmembers taking to the air with serious consequences. I have before now watched someone rigging a four-part pull between two vehicles, and needless to say I didn't hang around to see what came off. Rule 1 of winching - enagage the brain before any other equipment! |
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14th Jan 2015 2:16pm |
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| zone30 Member Since: 07 Sep 2012 Location: Gent Posts: 669
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I'd rather burn the winch motor or kill my battery then bend my chassis.
Hence I'm not keen on oversizing the winch. |
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14th Jan 2015 2:20pm |
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| roel Member Since: 08 Aug 2009 Location: Lelystad Posts: 2039  
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You are right with the double force etc. But a winch is bolted down mostly with 4 m10 bolts. My winch bumper is attached with 2 x M16 and 2 x m12 bolts and these are through the chassis so take load at 2 point at the same bolt. And this is at each side. So I am not afraid my bumper will be pulled off. It might rip off the whole front off my 90.  Roel
1984 90 2.5 na Diesel - RR V8 (1994-2001) 1997 Camel Trophy Discovery 300TDI (2001-2009) 2005 G4 Discovery III 4.4 V8 (2008-2018) It's gone but it still hurts. 2003 90 Td5 (2009-now) |
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14th Jan 2015 2:35pm |
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| leeds Member Since: 28 Dec 2009 Location: West Yorkshire Posts: 8582
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A minor correction for you BW 
Rule 1 of vehicle recovery - enagage the brain before any other equipment! Rule 2 If safe to do so, stop and have a brew Brendan |
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14th Jan 2015 2:57pm |
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| zone30 Member Since: 07 Sep 2012 Location: Gent Posts: 669
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You'd be amazed how many just dive in without taking the time to evaluate the situation.
Rule 3: it's better to get stuck then to break things. Only this Xmas holiday: going very much to one side near some posts => First goes through very slowly, no issuus. => Second a bit faster but gets stuck. => 3ths, as not to want to get stuck, floors is and hits a post (of course). Luckily only a scratch but cm from the roof side window. I was gesturing SLOW, but he wouldn't listen... Anyways, that's my rule. Rule 4: if you get stuck, stop. No sense in trying over and over when "the feet" are of the ground. You only get more stuck. PS getting stuck is halve the fun of off roading, together with just getting through |
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14th Jan 2015 3:05pm |
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| jst Member Since: 14 Jan 2008 Location: Taunton Posts: 8171  
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something else to consider when double lining on the speed front is you have more winch rope out too so a great mechanical advantage on the drum. so half the load with the pulley and smaller dia drum all equal better pulling, which means less current draw, less heat build up, greater efficiency in winch etc etc
in essence the more rope off the better if that involves a pully too then great! why run 100ft of rope if alot of winching is only from a short anchor point for example. i typically run shorter ropes on low line rear winches as pulls tend to be short. plus it quicker to add a short extension for a longer anchor point than it is spool it all out and then back in! Cheers James 110 2010 XS Utility 130 2011 M57 bespoke Camper 90 2010 Hardtop 90 M57 1988 Hardtop |
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14th Jan 2015 9:44pm |
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| mick Member Since: 08 Feb 2010 Location: Yorkshire Posts: 2109  
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If in doubt stick one of these on
 Click image to enlarge |
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14th Jan 2015 10:41pm |
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| roel Member Since: 08 Aug 2009 Location: Lelystad Posts: 2039
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You can not use that one when you motor isn't running.
Roel
1984 90 2.5 na Diesel - RR V8 (1994-2001) 1997 Camel Trophy Discovery 300TDI (2001-2009) 2005 G4 Discovery III 4.4 V8 (2008-2018) It's gone but it still hurts. 2003 90 Td5 (2009-now) |
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15th Jan 2015 6:06am |
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| Supacat Member Since: 16 Oct 2012 Location: West Yorkshire Posts: 11018 
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I'm not certain you are correct there. The force on the two fixing points on the vehicle (assuming you count them separately) is the same - the force is just doubled at the pulley end. There is nothing to stop you placing the return anchor end either on a separate vehicle or even an adjacent tree. Pulleys also have losses which will effect the mechanical advantage - 1 pulley 90% - 5 pullies 65% efficient. All of the above is redundant of course if you use a Tirfor  |
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15th Jan 2015 2:07pm |
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| Cupboard Member Since: 21 Mar 2014 Location: Suffolk Posts: 2971 
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say you're doubling the line back on to the bumper, the load on the winch will be ~halved but the load from the bumper to the chassis won't be.
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15th Jan 2015 5:45pm |
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| blackwolf Member Since: 03 Nov 2009 Location: South West England Posts: 17606
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I am correct. Neglecting friction, if you have a true 12k lb winch stalled on the bare drum with a double line, with the fixed end secured back to a blingy swivel shackle on the winch vehicle's bumper, then there is 12k lb trying to pull the winch off the vehicle, 12k lb trying to pull the blingy swivel shackle off the bumper, so in all 24k lb or about 11 tons trying to rip the front off the vehicle, and a similar force trying to rip the strong point off the other vehicle. Yes you can and should run the fixed end to a different anchor, but you also need to considef the attachment at the other end unless you want to watch it go by at a very high speed. My real points are (1) it is very easy to generate very high forces in a rigging system if you don't really know what you're doing, and (2) if you don't really know what you're doing err on the side of safety, read a book on applied mechanics, or learn the basics from someone experienced. The Tirfor is a hugely underrated tool in my opinion. An 800kg Tirfor has effectively the same capacity as an 8000lb winch, is a fraction the size and weight, pulls in any direction, works forever without the engine running, and can even work fully submerged, and costs less than a good drum winch. If you really want some versatile pulling power, a Trewhella monkey winch or a Trewhella Wallaby winch will make even a 3500kg Tirfor look like a toy, but they're less suitable for 4x4 recovery. |
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15th Jan 2015 6:31pm |
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| Supacat Member Since: 16 Oct 2012 Location: West Yorkshire Posts: 11018
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I'd read "all the strong points" as being individual points at which the forces were being measured; but happy to have a different clarification
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15th Jan 2015 6:34pm |
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