Thursday, November 24, 2016

Vehicle Recovery Part 2: Connectors

It's raining hard and you're trying to get out of town before the hurricane makes landfall. Friends are following you in a convoy to higher ground when one of the cars slides off the road into a muddy ditch. Now what?

In last week's post I covered what attachment points to look for on your vehicle when retrieving or towing it; this week I'll cover a bit about what to use to make the connection between the stuck car and the towing vehicle. You should select a connector that has a breaking strength of at least the weight of the stuck vehicle.  Bigger is both better and safer.

Regardless of which type of connector you use between the two vehicles, it is always a good idea to toss a blanket or tarp over it once it is tight but before you start to (slowly) pull. If a cable or strap breaks, the ends can whip in any direction and can maim or kill, but a blanket or tarp will provide drag from air resistance and slow it down.

(It works the same as using a piece of paper to break a ruler. If you never did it as a kid, get a wooden ruler and place it on the edge of a table so that half of it is sticking out away from the table. Smack the free end as hard as you want, and all you'll do is launch the ruler across the room. Now put it back in the same position and cover the end on the table with a sheet of newspaper. Strike the free end a sharp blow and the ruler will break in half. The paper will create enough resistance that the ruler will beak before the paper tears.)

Connectors break down into four main groups; cable, chain, rope, and strap. Here are the pros and cons of each.

Also known as wire rope, cable is made of several strands of steel wire twisted together to form a flexible connector.

  • More resistant to heat, abrasion, sunlight (UV light degrades most plastics), and chemicals than rope and straps. 
  • Like rope and straps, cable will stretch when a load is applied. 
  • Cable is more stiff, heavier, and more prone to damage from kinking that rope or straps. 
  • It can fray, with the individual steel strands breaking and protruding from the surface of the cable, causing nasty cuts to your hands. 
Best Practices
  • Cable comes in a variety of sizes and the breaking strengths are shown on this chart.
  • Inspect cables after use and always wear gloves when handling it.
  • Buy your tow cable from a reputable dealer with the ends already attached. Unless you work with it on a regular basis, cable can be a challenge to put an end on correctly.

Made of steel links that are welded together, chain comes in a few different grades or strengths. 
  • The common chain you will find at the hardware store is Grade 30, which is the lowest actual grade. 
  • Chains used by truckers to secure loads will be at least Grade 70.
  • Any chain used for overhead lifting should be Grade 80 or better. 
  • The various strengths of the different grades are shown on this chart, but notice the note on the bottom -- breaking strength is four times the “safe” working load.
  • Graded chain will have a stamp on a link at least every three feet. No stamp showing maker and grade means that it is a cheap imported chain that is best suited for decorative purposes.
  • Chain doesn't take a “set” if stored coiled up, nor will it fray. 
  • Similar in strength to cable, but chain is easy to splice or repair with readily available repair links and adding a hook to the end often doesn't even require tools. 
  • Chain doesn't stretch until right before it breaks, making it the most rigid connector. Rigidity is good when retrieving a stuck car but not when towing, where a bit of stretch will take the minor bumps out of a tow.
  • Chain is the heaviest option of all connectors.
  • Chain doesn't stretch until right before it breaks (see above).
  • Beware the decorative stuff. 

Natural or artificial fiber rope is easy to find but has a low strength-to-weight ratio. You're going to need a pretty thick rope to move a car with. Choose your rope by the breaking strength, which is usually three or four times the "working load". 

  • Rope is easy to work with.
  • Splices and knots are simple and easy to do,
  • Rope is inexpensive and common. 
  • Knots will reduce the breaking strength of your rope, the amount of reduction depends on the knot.
  • Storage can be a hassle; there's nothing worse than picking up a length of rope that is a tangled rat nest when you need to use it. 
  • Rodents love fiber for making nests, so store your ropes with care.
  • Natural fiber ropes are normally treated to repel pests, but the artificial fiber ones are not. 

Made of one of a number of artificial fibers woven together, straps share the flexibility of rope but store better. 

  • Most straps come with eyes on both ends for attaching hooks/clevises or looping around a hook. 
  • Passing one end of a strap around an object and then through the eye on the opposite end is a quick way to securely attach a strap. 
  • Splicing or repairing straps takes specialized equipment, so once they're damaged they should be removed from service.
  • Since the base fibers and construction of straps can vary so much, you need to determine its breaking strength. A good strap will have a tag sewn on near one end with breaking strength and other information on it; this is the only way to decide if the strap is going to be strong enough for your use. 
Last week I mentioned “snatching” or jerking a stuck vehicle out of a ditch. There are special straps that are made for this trick, they are more elastic than normal straps and will stretch before contracting and giving an extra “pull” to the car.

I should mention the different types of hooks and ends that you'll find on towing gear. Pictures will help. All pictures courtesy of Amazon. There are so many variables that I can't post links to them all.

This is a Grab Hook. It is designed so that it will “grab” a chain link and not move. Never use a grab hook on anything other than a chain since the edges will cut through cable, rope, or a strap once you put a load on it.

This is a Slip Hook. It is designed so that it will slip along the chain, cable, rope, or sling creating a tight loop. Slip hooks are great for hooking up to holes on a car's frame and attaching to other hooks. This one also has a safety catch so it can't fall off once it's attached. Notice the "G70" stamped on the side? It stands for Grade 70, so this is a transport chain hook.

This is a Clevis. It is designed to be placed through a hole to provide a better method of connecting a hook. Most of them are flat, but they are also made with a 90° twist if you need to change the angle of the hook.

This is a Thimble, used to create an eye on the end of a cable. Thimbles spread the load out and prevent the cable from kinking at the eye when a load is applied.

I hope this basic primer on towing connectors is informative, although I hope you never have to use the information. I work with farm machinery and we spend too much time dragging things out of ditches and fields for it to be fun any more. 

I prefer to use chains when I have to drag something since they are more versatile and durable than any of the others, but I also keep a tow strap in my own truck for emergencies.

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