More wenching stuff… sorry… winching….

Submitted: Sunday, Apr 09, 2006 at 16:22
ThreadID: 32705 Views:2087 Replies:7 FollowUps:10
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OK, I’ve got the Big Haul hand winch, tree trunk protector, load equaliser strap, a few rated shackles and an illuminated hat which reads “Winch Captain!” in flashing LEDs.

If I attach the tree trunk protector directly to the winch I’m going to have to sit on one of the tree branches to do any winching, so I need something between the TTP and the winch to get a bit of distance from the tree. To my mind about 3m of rated chain would seem to be ideal but I already have two rated tow (not snatch) straps which may also serve the purpose.

Question: I seem to recall that synthetic tow straps will stretch by about 10% (am I right?) and, if so, would seem to be an accident waiting to happen if used with a winch. Are winch extension straps any different or just tow straps in another package?

Can I use my tow straps of should I stop being a Scrooge and buy the chain?

Mike Harding

mike_harding@fastmail.fm
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Reply By: Member - Ed. C.- Sunday, Apr 09, 2006 at 16:44

Sunday, Apr 09, 2006 at 16:44
Stop being a scrooge and buy the chain!

What about a pic of that hat, and where can I buy one??
Confucius say.....
"He who lie underneath automobile with tool in hand,
....Not necessarily mechanic!!"

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AnswerID: 165967

Reply By: David from David and Justine Olsen's 4WD Tag-Along - Sunday, Apr 09, 2006 at 17:09

Sunday, Apr 09, 2006 at 17:09
G'day Captain

Winch extension straps are not kinetic straps ie they don't stretch and store the energy to release your wich like the moose in the beer add :-)

At least they don't stretch measurably.
AnswerID: 165969

Reply By: Gramps (NSW) - Sunday, Apr 09, 2006 at 17:33

Sunday, Apr 09, 2006 at 17:33
Aaah Mike, I was just getting interested with the 'wenching' bit and then you go and spoil it with a bloody winch :)))))))
AnswerID: 165973

Reply By: the real chopper - Sunday, Apr 09, 2006 at 18:29

Sunday, Apr 09, 2006 at 18:29
depends what you mean by "rated" with your tow straps.

buy the chain, you'll be amazed at how versatile and useful a rated chain can be.
AnswerID: 165986

Reply By: Wayne (NSW) - Sunday, Apr 09, 2006 at 20:35

Sunday, Apr 09, 2006 at 20:35
Mike,

I was asked the same question on Saturday afternoon while doing a winching demo on our driver training weekend.

The answer went something like this.

The reason that a chain is used is that it has a very high rating.
It can be adjusted to length up to 5mt, which is the standard length of a drag chain.
Drag chains have a loop on one end and a hook on the other.
With the chain passing through a bow shackle and then using the hooked end it can be secured to any length

The chain has other uses,
It can be used drag a tree from a track. If a tow strap is used it can be destroyed by dragging it through the dirt.

Winch extension straps come in lengths from 10mt to 30mt. They can be used instead of a chain and can also be shortened.

I tend to use a chain when the hand winch has to be secured up to 5 mt away from a anchor, further than that a winch extension strap is used.

Wayne
AnswerID: 166028

Follow Up By: Crackles - Monday, Apr 10, 2006 at 19:21

Monday, Apr 10, 2006 at 19:21
The chain may have a high rating but it's useful to remember when using a grab hook the safe working load must be reduced by 25% or 50% if choking the chain. A claw hook is the better option for shortening with no SWL reduction in a straight pull but they are rarely fitted to drag chains.
Same goes for winch straps. Double one over & you reduce the breaking strain by 50%. I wouldn't do that personally as that reduces a 5 tonne strap to just 2.5 tonne, well below the pulling capacity of many winches particually double blocked.
Cheers Craig.............
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FollowupID: 421126

Follow Up By: Scubaroo - Monday, Apr 10, 2006 at 21:55

Monday, Apr 10, 2006 at 21:55
How does doubling a winch strap over half it's breaking strain?
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FollowupID: 421175

Follow Up By: Crackles - Tuesday, Apr 11, 2006 at 19:01

Tuesday, Apr 11, 2006 at 19:01
Scuby I was wrong with the strap being half as strong. I got mixed up with wire rope which is halved if choked or fed around a tight hook etc.
By running the unprotected part of the strap around a D shakell or hook you are concentrating the force on the weakest part of the webbing. Depending on how tight the radius of the D pin is you can reduce the breaking point by around 20% turning a 5 tonne strap into a 4 tonne. Should idealy always use the reinforced eyes to attach a strap. Sorry for the confusion.
Cheers Craig............
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FollowupID: 421379

Follow Up By: Scubaroo - Tuesday, Apr 11, 2006 at 22:16

Tuesday, Apr 11, 2006 at 22:16
Sorry, I don't follow that logic - the loops on a strap aren't reinforced, they're just stitched into a fold, and covered with a wear sleeve. They would be subject to the same pinching effects etc from shackles and the like.

Seeing as in the stretch tests, most straps failed either by stitching failing, or the strap failing where weakened by stitching - I don't think any failed by the strap just "parting" somewhere in the middle - I still reckon that a doubled strap would increase the load capacity. Probably not by double, as the load to "tear" the strap at the point where it doubles around a shackle is probably less than double the single line pull rating, but I still reckon it would go up than down. Sounds like an argument that can only be settled with some similar testing in a lab.
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FollowupID: 421462

Follow Up By: Mike Harding - Wednesday, Apr 12, 2006 at 07:01

Wednesday, Apr 12, 2006 at 07:01
>I still reckon that a doubled strap would increase the load capacity.

I don't see how it could _increase_ the load capacity because at the point where the strap is in contact with the hook there is only a single piece of strap being subject to the full strain.

I think two straps together would increase load capacity but I doubt it would be doubled because the straps are not identical one would assume more of the strain than the other.

Any mechanical engineers care to comment?

Mike Harding
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FollowupID: 421503

Follow Up By: Scubaroo - Wednesday, Apr 12, 2006 at 11:55

Wednesday, Apr 12, 2006 at 11:55
The testing seemed to indicate that the load capacity of a strap was determined by the weakest point - i.e either the stitching breaking and coming undone, or the webbing where stitches had penetrated (and there's a ton of stitching there to make holes and damage the webbing fibres). Think of the sewing holes as "damaging" the strap webbing at that point.

So imagine if you will a "perfect" strap - no sewn weakpoints - the failure point of the webbing itself is probably much higher. If you could somehow loadtest just the webbing (dunno, giant flat clamps holding each end), 60mm webbing used to make an 4000kg winch strap probably fails at 6000kg - it's the damaged sewn portion that fails at 4000kg and gives the strap it's rating.

So I reckon the "loop" formed by doubling a piece of webbing through a shackle is much stronger than a sewn loop on the ends, because there's no stitching to either weaken the strap or tear out and fail at that point. But it wouldn't double the capacity of the strap - doubling a 4000kg strap to make an 8000kg strap simply won't work. But maybe it would get you 5-6000kg, and a shorter strap. The point is, the strap's rating would increase to whatever the rating of the webbing itself is, rather than what the rating of a stitched part of the webbing is.
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FollowupID: 421550

Follow Up By: Mike Harding - Wednesday, Apr 12, 2006 at 12:13

Wednesday, Apr 12, 2006 at 12:13
I see where you're coming from now. Sounds reasonable - the strap must have been weakened below it's original strength by the action of stitching so you're load sharing across the two eyes.

Yep, I can buy that you would get a stronger strap but by how much, as you mention, is a bit of a guessing game.

Mike Harding
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FollowupID: 421555

Follow Up By: Crackles - Wednesday, Apr 12, 2006 at 19:03

Wednesday, Apr 12, 2006 at 19:03
The weakest point on a winch strap is at the first stitching on the eye. When doubled the two eyes share 1/2 the load each but at the other end the unprotected middle of the strap is wraped tightly around the D or hook & now becomes the weak point. When lifting with fibre slings the safe working load of the strap is reduced by 20% if choked or doubled over.(as per ratings on the lifting gear or load charts) If looped around a larger pipe that is called a basket hitch & the SWL is doubled. It all comes down to how tight the radius is where it's secured in the middle.
A winch cable is similar too. You should never bend a cable tighter than 6 times it's diameter or you derate it's strength.
Cheers Craig..............
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FollowupID: 421674

Reply By: Scubaroo - Sunday, Apr 09, 2006 at 21:30

Sunday, Apr 09, 2006 at 21:30
I bought a "Just Straps" 3m equaliser strap from www.4wd1.biz for putting between the tree trunk protector and the winch (have an ARB Magnum) - it's basically a 3m 6000kg winch extension strap. You could get a 5m strap instead, but for $33... 3m is enough to get you away from the tree, and it's a cinch to handle compared to chain. Nice big 4.7t bow shackle at the TTP and one end of the 3m strap, and the other end of the 3m strap should attach directly to the winch using the supplied pin.

Figure that if I need more length it will be a winch extension strap at the vehicle end. Might be times when anything longer between the tree and the winch is ungainly.
AnswerID: 166054

Follow Up By: Scubaroo - Sunday, Apr 09, 2006 at 21:32

Sunday, Apr 09, 2006 at 21:32
Oops, meant 2.5m. There is a 3m strap rated at 8000kg as well.
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FollowupID: 420975

Reply By: Wizard1 - Monday, Apr 10, 2006 at 11:22

Monday, Apr 10, 2006 at 11:22
Get a drag chain. They come in handy to drag trees off tracks etc, which I've had to do and that type of work wrecks a strap in no time.

Wizard
AnswerID: 166132

Follow Up By: Leroy - Monday, Apr 10, 2006 at 12:17

Monday, Apr 10, 2006 at 12:17
yep drag chains are the go. If you don't have one you can as pointed out above use them for other things.

Leroy
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FollowupID: 421065

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