Winter Stuck/ Recovery Thread 2012

[SKR]

I disagree with all of this, but I can't explain it any further than I have if I can't get the terms right. I'm not conceding defeat, but obviously I'm at my limit.

Maybe I need to actually see it to believe it. If anyone wants to keep taking a run at it, pm me rather than making everybody watch this go back and forth, and then if we can come to an agreement we'll post it here. We're already at 3 pages. I don't know if we need to make it any longer.

Edited to add: I fully expect my inbox to stay empty. I'd be very surprised if there are any sadists here who haven't had their fill yet.

For the record, I have a thing like this that slides into my receiver:

http://patentimages.storage.googleapis.com/EP1918134B1/imgf0003.png

I don't have a ball to pull with either.

[lilmira]

:rofl: once everything starts to move and stretch, it's a whole new level of clusterfuck. Yeah highschool was long ago for me too.

Berserker, I was thinking more about the inertia of the cable than friction. Imagine pulling a big block of jello in space, SKR's thinking has some merit even though it's insignificant to the situation being discussed.

You don't have to thank me for bringing in a big block of jello into the discussion. ;)

[BerserkerCatSplat]

Originally posted by lilmira
:rofl: once everything starts to move and stretch, it's a whole new level of clusterfuck. Yeah highschool was long ago for me too.

Berserker, I was thinking more about the inertia of the cable than friction. Imagine pulling a big block of jello in space, SKR's thinking has some merit even though it's insignificant to the situation being discussed.

You don't have to thank me for bringing in a big block of jello into the discussion. ;)

You're quite right about the Jello in space! You're also correct that in the real-world case the inertial force is quite negligible. :D Mmm, jello...

For those joining us late in the thread, please don't attempt to use Jello as a recovery device.

[AndyL]

Jello so has a place in vehicle recovery ;) half digested jello shots are a fantastic friction modifier:D makes a car slide better than the spraybottle of dawn/water could ever hope to...

I decided to just not get into the physics of recovery, once the post got to 2 pages long in openoffice writer, decided it was better to just let it be...

[syritis]

Originally posted by SKR


If you put 1KN into it and all it does is stretch the strap, then Vehicle 1 is seeing 0KN. If it is going to take 1KN to pull the vehicle, and 1KN is going to stretch the strap, then you need to apply 2KN. This is Force A+Force B. The only way that you can apply 1KN on one end and have the full 1KN transfer to the other end is if the strap doesn't stretch.

i'm goign to completely through actual math out the window because i simply don't know the formulas so here is the simplified version.

if a 3meter strap is designed to stretch 10% with 1KN and vehicle A moves forward 3cm the strap it's now 3.03m. it is applying 0.1 KN to both vehicles and has 0.1KJ of stored energy.

if Vehicle A moves forward 30CM it has now reached the 10% stretch and it now at it's max length. the strap is now 3.3m long it is applying 1KN to both vehicles and has 1KJ of stored energy.


so it took 1KJ of energy to impart 1KN of force.
1KJ : 1KN (not actually but as an example)
1KJ + 1KN does not : 2KN

[lilmira]

You threw math and physics out the window alright, stay away from the jello shots.

Consider statics only, say you are pulling this truck just hard enough to overcome the friction F but not enough to accelerate. So you, the rope and the truck are moving at the same constant velocity V. The tension in the rope is also F. Say the cable stretched 3cm under tension F. The energy stored is (kx^2)/2. k is the spring constant, x is 3cm.

Now consider the dynamics once the cable snaps. Both pieces of rope will go back to their original length. The stored energy is released in terms of kinetic energy of the flying rope, sound and heat. No one is pulling the truck anymore, it will be stopped by friction. Depending on how quick your reaction is, you'll most likely fly away in the opposite direction and land in the dirt because your legs are still pushing, then the flying rope may or may not hit you in the back of your head.

[syritis]

Originally posted by lilmira
You threw math and physics out the window alright, stay away from the jello shots.

yup. I'm aware my numbers were completely wrong, just made up some vague numbers to make the example that the strap does not magically apply more force to the stuck vehicle than what the tow vehicle applied to the strap.

[spikerS]

Thought I would bump this up in case the weather tonight proves too much.

[speedog]

Well it is getting downright greasy out there - just came back from Speeders and the roads are quite slick.

[Twin_Cam_Turbo]

I ALMOST didn't make it home from Coventry to Hamptons, got completely stuck on Country Hills on a uphill when I had to stop for a light. Took 10 tries to get moving after that, thankfully nobody behind me.

[FraserB]

Roads are bare up here in Edmonton:poosie:

[syritis]

I was laughing at people pretty hard last night. watchign them jump on the brakes and sping 180* like they got hit by a turtle shell.
even more ironic you could tell exactly who was gunna spin. driving with no lights on. driving slow in the fast lane. wipers going fast enough to break orbit....

I may go out for a drive to pull some people and get food.

[RjKaz]

Nylon tow strap / rope warning - I didn't read entire thread to see if danger was noted.
We used heavy nylon for heavy equipment, the stretch seemed to help as long as it didnt break, but always a big recoil if they broke. We still didnt sense how dangerous until my uncle was killed using one - just a 1/2 ton truck pulling out another 1/2 ton- the metal clevis broke on the towed vehicle, and the nylon rope recoiled. Part of the metal (in the recoil end) went through his tailgate and the rest went over the tailgate through the cab.

After the accident, we scrapped all nylon tow ropes and use heavy chains - they still break but don't recoil. On some of our heavy equipment, we can order a tow harness that is a short heavy steel cable fastened to a designated anchor point, and we hook to the end of that. The point here is that I'm guessing heavy cable is also safe from recoil.

I've also heard that polypropylene does not stretch like nylon and is much safer. Maybe this is all old news, and perhaps nylon isn't sold for tow ropes anymore....

[FraserB]

Its been beaten to death, a tow strap is not a snatch/recovery strap. You should NEVER us a tow strap or for recovery. Never use a cable as a snatch/recovery strap.

[RjKaz]

Maybe I'm unclear on the term 'recovery' and the comment to never use steel cable. We own large machinery - the steel cable is provided (extra cost) by the manufacturer. It's typically about 10 feet long, and anchors to the frame at the designed location, the other end of it hook to a chain or cable. This is used for heavy machinery when it is stuck - would seem to apply to cars.

Rather than full explanation, just point me to the exhaustive dialogue. But since these are recents posts, probably doesn't hurt that people towing or being towed for 'recovery' (unstuck) are refreshed on it. I'm concerned people are talking about the stretch, cause that sounds like recoil if something fails.
What do you use to tow?

[FraserB]

Towing=/ recovery

Tow straps have no stretch in them and are designed for towing. Most have hooks attached to them which can turn into a projectile if the line breaks.

Recovery/snatch straps have about 20-30% elasticity in them and will fall flat if they break, the kinetic energy generated by that stretch helps in the recovery. Tow points breaking and flying is just a sign of a shit tow point or one that has been overloaded, that is when they will turn into a projectile.

Steel wire, like the stuff used with most winches stores energy and if it breaks, will whip around. Synthetic stores far less energy. Jerking on chain is simply asking for trouble.

Heavy equipment is far different than cars and smaller trucks.

Personally, I don't use straps or cable to tow. That's why they sell trailers. For recovery, synthetic recovery straps with a rating of 24,000lbs. Shackles that are rated for higher than needed for the vehicle, properly secured tow points and a weight bag hung on the strap. I haven't upgrade the winch to synthetic yet, but it always gets a weight hung on the line when in use.

[syritis]

^^ all of this.

[RjKaz]

Originally posted by FraserB
Towing=/ recovery
.....
Heavy equipment is far different than cars and smaller trucks.

Personally, I don't use straps or cable to tow. That's why they sell trailers. For recovery, synthetic recovery straps with a rating of 24,000lbs. Shackles that are rated for higher than needed for the vehicle, properly secured tow points and a weight bag hung on the strap. I haven't upgrade the winch to synthetic yet, but it always gets a weight hung on the line when in use.

Wow, just checked through, this was beat to death. When i read the first bit about people offering to give people a tow, I thought safety/equipment needs to be hilited. I see it was.

FaserB - good summary points, but a few comments. We aren't talking about towing people down the road - I get it, should use term 'recovery' but note any reference to 'tow' throughout the thread is used in ref to getting people unstuck/recovery, we don't want to debate trailering here....
Most important, heavy equipment is NOT different than cars and trucks, the same physics apply, and so the same issues. ... same practices/protocol apply to pulling a car out of the ditch. Pulling a car might appear less risky than equipment.

I won't say tow again. The nylon 'tow' ropes we used were 'recovery' ropes. The issues arose when something broke. Best advice in any recovery or tow, if you must be involved, be extra cautious to assess failure points and eliminate them. Best advice I read came from Speeddog, that helping seems the right thing to do, but recovery is perhaps better left to someone trained, with proper gear. Neither 'Joe' with a truck and a rope/strap, or the person being pulled, may know what they are doing.

[btimbit]

Well, little late in the season but I'm expecting at least two more days of crap driving, so I guess I can re-re-add me to the list now that I have a truck again.


Brandon
4o3-471-o275

-'07 F-150
-20ft tow strap (17000 lb)
-Booster cables

Note that right now I DON'T have a recovery strap, I think I left it in my Sierra when I sold it. Like before, I know my limits so worst case scenario you have someone to grab coffee with and hang out with until professionals arrive.