Weakest point in winch and rigging?

[jcbrandon]

Ideally, where would the weakest point in your complete winch and rigging system be, if you could intentionally put it anywhere?

Think of a fuse. The weakest point of a system designed to fail first with the least amount of damage. Also, ideally, easy to replace.

I ask because I recently bought a truck with a Warn 12,000-pound winch installed. I'm learning everything I can with an emphasis on separating hearsay and anecdotes from facts. Prior to posting this question I searched the ExPo forum for the words "winch" and "cable" and read some great stuff. Thank you to all who have contributed to previous threads, especially this one on "synthetic winch line."

The winch came with 90 feet of 7/16" wire rope. I'm having difficulty determining the safe working load and breaking strength of that wire rope.

I also bought a snatch block (Warn part number PN 15640) rated at 24,000 pounds. I was more than a bit dismayed when I opened the box to discover cast into the side of the housing "WLL 4 1/2 Ton." So my 24,000-pound block is only rated for a safe working load of 9,000 pounds, yet the manufacturer recommends it for use with a 12,000-pound winch.

So trying to make sense of all this brings me to the fuse question. And that leads me to wonder exactly what would happen if I put 12,000 pounds of stress on this winch. Would it just stall and quit? Overheat and burn out the motor? Would something break?

If I beef up one part of the rigging, will that have unintended consequences? Would I transfer the weak point to somewhere I don't want it to be?

 

[AndrewP]

WLL ratings are for overhead lifts, and typically 4X breaking strength. That snatch block sounds fine.

7/16 cable is big stuff and typically a 12000lb winch will come with 3/8 cable.

I would not intentionally build a "fuse" into anything that comes under load. I did think the shear pin in the old Toyota PTO winches was a decent idea-it was designed to shear before the cable broke. If you really plan to pull that hard, watch what you connect to carefully.

Most extraction pulls offroad are in the 3000-4000 pound range, unless pulling a huge truck out of deep mud, or a completely dead tuck up a difficult spot.

 

[ntsqd]

I've also noticed what Andrew touched on, that self extraction components regularly exceed the WLL of equivalent industrial rigging by a large margin. Apparently OSHA has no say in self-extraction. Anything that lifts or supports humans, or lifts something potentially lethal above humans, usually has to have a Factor of Safety of at least 4 and sometimes 5. So at best a 5000 lbs tensile strength wire rope could only "legally" lift 1250 lbs.

I guess my concern over a fuse in the system would be what happens if the fuse blows? Does the cable go slack? That would be a major bad thing.
If all of the equipment and anchor points are equal to or exceed the strength of the winch, then the 'fuse' would be stalling the winch motor. I see that as the most ideal set-up.

FWIW, Sampson lists their Amsteel Blue in 7/16" as having an average breaking strength of 23,900 lbs.
Wire Co. lists one of their 7/16" wire ropes as having a average breaking strength of 15,600 lbs.

 

[mog]

If all of the equipment and anchor points are equal to or exceed the strength of the winch, then the 'fuse' would be stalling the winch motor. I see that as the most ideal set-up.

A +1 with ntsqd. If everything, cable, blocks, anchor points (both on and off the vehicle) exceed the winch's rate, it should stall out prior to anything letting go. Probably the most desirable effect, since you still should have tension, nothing 'letting go', so only a "dang, I need more power". And with a 12,000 winch plus a snatch block, I would hope you should be good to go.

 

[IggyB]

IMHO the weakest link wouldbe the cable itself. 3/8" cable is rated at 12000 lb nominal strength. That's the only rating it has, there is no 4:1 safety margin.

So if you take brand new 3/8 rope as good for 12000 lb,
once you wrap in on a 4" diameter winch drum it's detated a certain amount,
once it's used and has a kink or two or has been pinched it's derated again.

So after a short while the rope is weaker than the winch.

 

[ntsqd]

The problem there is when the 'fuse' blows you have a very, very dangerous condition. One to be avoided at all costs. I have seen pictures of the aftermath of a snapped cable. It is not pretty and can be very deadly.

If you opt for one of the poly ropes the severity of a snapped rope drops significantly, but what then happens to the vehicle that was being pulled by the winch?

 

[Bill Beers]

And that leads me to wonder exactly what would happen if I put 12,000 pounds of stress on this winch. Would it just stall and quit?

It will still reel in cable w/a 12000 pound load attached. Keep adding load over the 12k and and eventually the winch will stall. Warn winches are very tough. Heck, the 9.5 XP will pull 12k.

Overheat and burn out the motor?

If you keep trying to winch after it's stalled, you'll mess up the motor. If you keep winching after your motor gets too hot, (which can/will happen at less than the rated load,) you'll mess up your motor. The new Powerplant winches have a thermal load cut off switch that will protect your motor from heat damage.

Would something break?

Eventually, I suppose the cable would break. Or if you have a crappy bumper, it could rip off.

The worst case I could think of is a dead truck in the mud, there you have suction working against you and nothing working for you. If the truck is still driving, that takes load off the cable.

-Bill

 

[madizell]

The safety fuse in a self-recovery system should be the guy with his thumb on the switch. Motor overheating? Wait 5 minutes and try again, or go double line pull. Motor stalled? Double line. Motor stalled while pulling double line? Yikes. Assuming that all electrical components of the system are at least rated for the system, and the alternator and battery are at full capacity and will support the demands of a 12,000 pound winch, stop winching and find another solution. Triple up the line if equipment is available. Dig out the axles, frame or whatever. Remove large obstacles from in front of the axles. Reset the line of pull to reduce or eliminate angles. Get more than one truck in on the pull.

I have seen 12,000 pound winches stalled lots of times, but only when they were not working to full capacity or did not have enough electrical or hydraulic support. A truly good and correctly working 12,000 pound winch will pull an enormous load, and on a standard truck, can bend or break frame components, especially if not hooked up correctly. I have tweaked the frame on my CJ-7 with only an 8,000 pound winch by pulling more than I should, off angle (diagonal stress). Better not to use the full capacity of such a winch unless you are pulling on a 2-ton utility truck, which is to say you should not see the winch stall under normal self-recovery scenarios.

Best not to have the line break, no matter what. Especially with something as heavy as 7/16 steel line. It could get ugly.

 

[jcbrandon]

Thanks, ya'll; I appreciate your insight.

The winch on my truck does have a thermal protection circuit. So it seems that is along the lines of my thinking on building in a sort of "fuse". If I try to exceed the capacity of the system, the winch will just decide to take a rest. No harm, very little danger, and maybe while it cools down I'll rethink my rigging set up.

It appears that the next weakest point in the system is the cable. If it fails, things can go very bad. But all things considered, if something is going to break, the winch cable might be the least evil.

I'm considering upgrading to a synthetic cable. This will almost certainly be stronger than the existing steel. Since the current wire rope might be over-designed, I could probably gain extra winch line length by going to a smaller diameter synthetic which would still be stronger than the existing steel.

Sounds like I'm good to go. Unless I've overlooked something...

 

[Michael Slade]

The weakest link in any winching scenario is always the operator/rigger. The equipment is only as good as the knowledge that was used to set it up. Know the gear.

The moment you forget that your equipment can kill you, it will.

 

[madizell]

The winch on my truck does have a thermal protection circuit. So it seems that is along the lines of my thinking on building in a sort of "fuse". If I try to exceed the capacity of the system, the winch will just decide to take a rest. No harm, very little danger, and maybe while it cools down I'll rethink my rigging set up.

It appears that the next weakest point in the system is the cable. If it fails, things can go very bad. But all things considered, if something is going to break, the winch cable might be the least evil.

I'm considering upgrading to a synthetic cable. This will almost certainly be stronger than the existing steel. Since the current wire rope might be over-designed, I could probably gain extra winch line length by going to a smaller diameter synthetic which would still be stronger than the existing steel.

Sounds like I'm good to go. Unless I've overlooked something...

A thermal over-ride is not a safety fuse. It only protects the motor internals from excess heat. Lots of things can go wrong before the motor heats up, if it ever does. Try not to make assumptions based on the presence of a thermal cut-off. Generally, a thermal cut-off will operate when you are making long, continuous pulls within the working range of the winch, but outside the duty cycle of the motor. You will more likely break a cable or rope early on in a recovery while the winch is operating with a cool motor.

A broken cable is not the least evil a winch can sustain. Low batteries can be charged, connections restored, bolts replaced, jammed cable can be unjammed, solenoids can be replaced in the field, and so on. Cable, on the other hand, is dangerous when loaded, and in order to break, has to be loaded to the breaking point. Steel cable is heavy and stores energy, and when it breaks, it has lots of sharp little teeth that slash around without warning. This is why you should never be anywhere near the cable or the line of pull when winching.

It is also quite difficult to field repair cable or rope, either one. I have yet to see a successful field repair of rope by tying a knot, and cable can't be spliced or knotted, and clamps in line are not safe or adequate. Once broken, it seems that neither rope nor cable are long enough to do the job anymore. Best to carry a spare if you think breakage is possible. Cable is not especially expensive, but is heavy; rope is not heavy but is especially expensive, and has to be spliced to a hook to work at all.

The strain rating of rope versus cable suggests at a glance that rope is stronger. This is rarely the case, however. Both break in the field for a variety of reasons. Rope is not resistant to abrasion or to sharp edges, and loses strength when bent around a fairlead. Assume rope to have only 50% of its rated strength and you will be in the ball park, and such an assumption will put you right back down there with equivalent steel line.

Rope will usually give you more length to work with, but this is not always an advantage. All winches are rated for maximum pull on the first wrap on the drum. If you have to drag an extra 50 feet of line off the drum to get to your full pull rating, you will limit your anchor points unless you are always having to reach anchor points in the next county. Most recoveries are within the first 50% of the line, which leaves you with a de-rated winch to start with. The 7/16ths line is probably overkill, but more and lighter strength synthetic is not necessarily the answer either. Rope also is susceptible to damage from sunlight and heat whereas steel line is not.

I consider synthetic line to be disposable, one-season equipment. After that it is suspect. It might be fine, or it might not. Keep in mind that the colorant used on rope is there for UV protection and lubrication. Once the color is gone, so is the protection, and there is no way to gauge the remaining strength in frayed or sun-damaged synthetic line. I would use synthetic rope of the same physical size as the wire rope it replaces, or one size larger (much of the synthetic rope is actually metric -- get the best you can afford but don't go down in size).

All that said, I would not worry about it. Use it safely, keep your fingers out of the fairlead, don't handle tensioned line even with gloves, always wear gloves even with synthetic line, don't take chances, and before you know it, you will understand your system very well. It is stronger than you might think.

 

[AndrewP]

Good post madizell.

In a former life while in college, I was a rigger on a crane in the summers. I have worked with and around wire rope, and respect it very much. I much prefer it to synthetic line. I know that is heresy here, but the steel stuff is tough, resilient, cheap and more than adequate for the job.

In 10 years of 4 wheeling and occasional winching, I have never seen wire rope fail. I know it can, but I've never seen it break. I have seen or been involved in dozens of winch operations/recoveries. We always take precautions with line weights and the like. The most important precaution is to be conservative about winch pulls, and to double line even in borderline situations.

Synthetics, on the other hand, I have seen fail several times often at low loads. An unseen knick in the line and it will fail right there with no warning. Fortunately, it doesn't store a whole lot of energy, or cause much damage (mostly because of it's light weight). I like the idea of one season disposable line, but that gets expensive pretty fast.

Anyway, the whole WLL thing is mostly irrelevant to off-road recovery. When is the last time you saw a shackle fail? The common 3/4 inch ones are only rated near 4 tons, yet no breakage even with the cheap chinese made ones. I did see a tow strap fail once and that was pretty cool and didn't do any damage.

 

[ntsqd]

FWIW the Sampson page does have an article on splicing the 12 strand synthetic ropes. It is geared towards making eyelets into the end(s) of the rope & requires a fid.

I spent a day with some 1/4" Amsteel looking into possible field repairs and testing them to failure. Short of the eyelet splice (& resulting shorter line length) there was only one join method that I discovered that would fail the line rather than the join. No known to me knot would fail the line. All failed in the knot. I used to rock climb, so knots are nothing new to me and I did research possible options in the couple of knot reference books that I own prior to the testing. Even the so-called "Grapevine" knot commonly used in rope slings on climbing anchors failed at the knot. Characteristically all of the knot failures looked like the line was overheated.

However, a simple 'S' weave, repeated at least 5 times, passing one end through the other line at 90* repeatedly failed the line on either side of the join. A tool like a dull pencil is required to carefully work the line's weave open enough to pass the end through. It is a viable field repair that I would trust for a "Getcha Back", but advise anyone considering it to test it on a sample of their own rope first. And, of course once back home that whole line is scrap.

Madizell's comment about retiring ropes reminds me of the rules for doing so in rock climbing. Those rules, adjusted to the different type of use, would be a good place to start formulating a set of rules for retiring synthetic winch ropes. Age is only one factor in determining when a rope should be retired.

 

[madizell]

The "S" weave is part of the process of splicing on eyes and hooks in synthetic rope, and is worth a try if a rope fails in the field and you have no spare or any other options readily at hand. Also part of that process is running a length of one rope down the center of the other like a Chinese finger cuff. A combination of burying a length of one line inside the other, and "S" tucks at both ends would likely join a winch line sufficiently to be used. It should be replaced after that as soon as possible, even if the splice works.

Splicing instructions are available from most if not all of the rope manufacturers and distributors (source, not retail) such as Puget Sound Wire & Rope, which company distributes so-called "plasma", the high modulus poly rope that I prefer. Splicing routines are the same with all 12-strand ropes because the method is specific to 12-strand construction, not to the material from which it is made.

Knot strength relative to line strength is one of those things that we probably learned as Boy Scouts, but have since forgotten. The attempts at knot repair I have seen were all in competition under duress, and ended up looking like multiple Granny's. They don't work as a rule. Any knot which allows the tensioned lines to enter the knot at an angle all create a stress point that causes synthetic line to fail at the stress point. Heat from choking the line could be a factor, but analysis of line failure is difficult without equipment.

It should suffice to say that, for our purposes, failure of a winch line in the field should not be thought of as a viable option or preferred result.

 

[MuddyMudskipper]

Nice posts Madizell!