Quick recovery question

ReadySalted · Nov 9, 2011

Hi,

I was on the OLLR forum today just nosing around and looking at their members photos, and came across this pic:

Now, I do a bit of climbing, (as in rock), and one of the first things you learn when setting up an anchor for climbing, is never to use that method. It's known as the american triangle, and I've heard people call it 'death triangle'.

The reason is because by having the two anchors (around each of his leaf spring shackles by the look of it), it puts more strain on each of the anchors (i.e. his leaf spring shackles).

I've seen 4x4 owners use it before and just wondered why it's commonplace in the 4x4 world, when it seems almost forbidden in the climbing community.

I know that 4x4s are alot stronger than pitons and climbing gear, but it's still effectively doubling the strain by using two anchors in this way.

ReadySalted · Nov 9, 2011

Just found this if you want to do the maths. American death triangle - Wikipedia, the free encyclopedia

jamesmartin · Nov 9, 2011

works and does spread force through two anchor points whatever angle pull is ,unlikely to pull spring hangers together ,not suitable comparison

easye1 · Nov 9, 2011

Hi,
as I dont do laning, offroading yet, or rock climing,
but was once an engineer,
my thoughts are,
some old landies are rotten, so anything that`ll hold a rope tied to its a bonus!

(as I hide my ears and walk away)...

ReadySalted · Nov 9, 2011

I've no doubt it works. Just it seems unessecary. The blue lines on the diagram show the direction of pull on the anchors. It's to do with vectors. The load isn't spread amongst the two, you may as well just use one anchor point. I just wondered if there's a specific reason why this is used in 4x4 recovery.

jamesmartin · Nov 9, 2011

your thinking about it in the wrong way ,obviously with a triangle you have a vectored pull ,which with tent peg would be extremely important but if you fastened to one spring hanger it would take all the force 2 shares it if not 100% equally,looped around like in picture allows rope to move adjusting point of pull and keeping some strain on both hangers ,more damage is likely to occur on one point than the chance vectoring will have an effect

ReadySalted · Nov 9, 2011

Ah okay I see what you're saying now. Because each anchor is several times stronger than it needs to be for the strain of a stuck landy, it's easiest to use this method for simplicity, and speed's sake. Gotchya.

blue beasty · Nov 10, 2011

Better to attach to both spring hangers than loop around though....even if you use a rope as shown it would be greatly improved with a clove hitch at hangers..then the vectors are in line with the rope

jamesmartin · Nov 10, 2011

does depend on whether angle of pull is variable or fixed but there are other ways of letting pull point on rope move without loop .which is easy cheap and works

ricc · Nov 10, 2011

if you go on one off center point the towed vehicle tends to slew to one side... which can lead to a harder pull with wheels sliding diagonally in ruts.. the triangle gives a more central tug and an easier straight tow

300bhp/ton · Nov 10, 2011

Putting a rope around spring hangers would be a no no in competition. Also lots of sharp edges to cut thought the rope. So on that basis alone I think the pics in the OP are wrong.

OP - I'm not sure I follow 100% on this. But is it because it's a single bit of rope that is looped that is the issue?

I can't say I've ever seen anyone being recovered in the fashion of the pics you posted and it certainly wouldn't be advisable under ALRC regs and competitions.

I presume had it been attached like using a rope with the ends attached to each chassis leg, rather than looped round, then you'd view it differently?

e.g.

a short rope attached to a chassis shackle on each chassis leg. You'd then have a 2nd rope attached to the middle of the first one then to the back of the recovery vehicle.

jamesmartin · Nov 10, 2011

theres a bigger world out there than ALRC regs,fastening rope to attachments would obviously protect rope and attaching 2nd rope to the first so that it could slide would be better but would still give the triangle op was talking about

300bhp/ton · Nov 10, 2011

jamesmartin said:
theres a bigger world out there than ALRC regs,fastening rope to attachments would obviously protect rope and attaching 2nd rope to the first so that it could slide would be better but would still give the triangle op was talking about

ALRC regs are based off MSA regs... so yes there is a bigger world. But I doubt any reputable organisation would advise rope fitment as per the pics in the OP.

And no, it's not the same triangle - that was my point.

There's no 3rd side to the triangle in my example, only 2 sides.

jamesmartin · Nov 10, 2011

the point he was making was not the best securing method but when you pull from two points as in pictures whether or not its from jate rings or ropr looped round it forms a triangle so load has a vectored pull in that some of the force is going to try and pull chassis legs together in either method, whether there is a 3rd side or not ,in climbing i could understand why this might not be the best method but pulling a lr is different

300bhp/ton · Nov 10, 2011

jamesmartin said:
the point he was making was not the best securing method but when you pull from two points as in pictures whether or not its from jate rings or ropr looped round it forms a triangle so load has a vectored pull in that some of the force is going to try and pull chassis legs together in either method, whether there is a 3rd side or not ,in climbing i could understand why this might not be the best method but pulling a lr is different

Maybe I got it wrong, but I don't think the op was saying about the actual attachment method, I thought it was about the loop making a triangle, so that when you pull, each locating point gets pulled from two directions and hasn't actually split the loading.

e.g. in the OPs pics, when the vehicle is pulled, the rope on the right hand spring is not only applying force pulling the spring away from the vehicle, but is also pulling it sideways towards the other spring. The same happens on the other side. So instead of splitting the loading, you are actually applying all of the loading to both sides, only in different directions.

In short, it's trying to squeeze the two chassis legs together as much as it's trying to pull the vehicle forwards.

That is what I believe this diagram shows:

Compared to what I was saying:

I've added the black arrows where I think the direction of pull would occur with this scenario. Which would seem to indicate that this approach would not try and squeeze the chassis legs together and overall achieves quite a different result.

However, I don't know this for sure, so please feel free to correct my guesses.

jamesmartin · Nov 10, 2011

you would still get the same vector with both ways of securing rope

ReadySalted · Nov 10, 2011

I'm afraid the pull isn't the same.
300bhp/ton has got the idea. If you use the triangle in the way pictured, pulling say a 1 ton strain, then each anchor will have a force applied to it of one ton, in the direction of the blue lines.

Wheras if you use the method in the second diagram, then the load IS spread between the two anchors. Of course what it doesn't allow for as easily, is multi-directional pull.

What I am about to describe is probably too faffy for vehicle recovery, since you just want to hook up, and pull it out as quickly and safely as possible. However, in climbing you use one of the two methods in my diagram.
In the first one (left hand diagram), there is a continuous loop of rope, which means that you can still have multidirectional pull, and the loop of rope going to each anchor will shorten/ lengthen itself as you move the direction of pull to the left or right. All you've done is simply pulled down the top bit of the 'triangle', and secure it in the D-Shackle, so that it now makes a V shape instead of a triangle. This makes changes the vectors, so that the load is now shared between the two anchor points.

Slightly more complicated is the diagram on the right, where you have two separate ropes going from the D-shackle to each anchor on the stricken vehicle. The downside of this one, is that it needs more equipment, and the only benefit, is that it offers redundancy, which isn't really that important when towing vehicles.

Stuballsed · Nov 10, 2011

Hmmm, would love to see the maths on this, but, as an engineer, whom can't be arsed to do the math; like JM says, the force applied on the bottom single point of the triangle, would be spread across all points of the trangle. Even if there is no rope connecting the top two points together, there would still be a force pulling these two points together.

Imagine laying the rope out on the ground, in either scenario, without connecting to the vehicle. Now pull the bottom point down. The two top points will move towards each other. This is what they are trying to do when connected to the vehicle.

IMHO

jamesmartin · Nov 10, 2011

if angles are the same the vector will be the same ,doubling up rope is no different than using single double strength rope ,admittedly not so easy if climbing,but easy with vehicle,the two methods of having sliding connection is the same as i described earlier which will allow a force still to be exerted on both points even if unequall where second could have force just down one and other slack .your moving your argument from vectors to how the best securing method

Stuballsed · Nov 10, 2011

jamesmartin said:
if angles are the same the vector will be the same ,doubling up rope is no different than using single double strength rope ,admittedly not so easy if climbing,but easy with vehicle,the two methods of having sliding connection is the same as i described earlier which will allow a force still to be exerted on both points even if unequall where second could have force just down one and other slack .your moving your argument from vectors to how the best securing method

Trying to get my head round this. Just checked out the wiki link. I dont quite understand how you can end up with more force being applied at the anchors than you are applying to the load point of the triangle. But I quess thats the vector maths magic. So, the OP is right? The rope set up in the OP will results in greater forces being applied at the anchors than if the rope was tied to each anchor separately.

Edit: The wiki maths indicates that the original load of 100lbf is exceeded at the anchor points at a bottom angle over 60 degrees. So I guess, its at this point that you are not spreading the load, you are multiplying it! So, is the lesson to be learnt here, that its best not to do it, but if you do, make sure it's not a short loop of rope that gives you a bottom angle over 6o deg.

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