Big Snatch

[codz]

Cody I only used that particular knot in the photo so it was easy to see that it was all one line. I'd use a clove in real life, so long as its secure. Way stronger, without the bite. And a 3 strand works similar to rope-on rope anyway, where there's a bite or a bend i.e. 3-strands. Where they run through the shackle also, they'll near always run side by side in the bow, no cross-over.

 

 

Well of course there are, but thats not the point, you only had one line in the video, that's what I'm going one.

 

 

 

Absolutely, and I dont intend to be double-roping a 40mm rope any time soon either. Again, my point was to show an example of how to potentially increase your safety factor with a limited amount of hardware, while offering an alternative to the configuration of that 40mm you had there in the video. Not trying to compete with or undermine you, just sharing something that has worked in the past for me.

 

I will have to come back to this one later, the Missus just went into labor.

[Steve Bullman]

I will have to come back to this one later, the Missus just went into labor.

 

From reading this thread no doubt

 

Good luck

[Stephen Blair]

Good luck!

[codz]

I will try and get her to snatch load it.

[waz77]

Brings a new meaning to the term "big snatch"

Hope all goes well.

[RC0]

I will have to come back to this one later, the Missus just went into labor.

 

All the best

[joe into trees]

Well, I'm pleased to report that Codz has added a healthy baby girl to his growing family...

 

Back on to the original video, however...

 

you only had one line in the video, that's what I'm going one.

 

Perhaps a more constructive way of having this discussion is, as RC0 suggests, to try and come up with better setups using the hardware available.

 

Obviously, if we wanted it to work, the simplest solution would be to take a smaller piece. Next up, use a bigger rope, or somehow get hold of a 40mm rigging block that we didn't mind throwing away afterward.

 

However, what we managed to source was:

120m of 40mm Aquatec 3-strand rope (approx 25t break, 7-8% elastic elongation at break)

1 90t shackle

10 40t shackles

we also had the usual 100m lengths of 12t (18mm) - 18t (20mm) dbl braid and matching pulleys.

 

The piece we snatched was a fraction under 5t, and the rigging point was at about 35m in height. There was a convenient stub right there (OK, we left it deliberately) on which to take a wrap for natural-crotch rigging.

 

Re. previous suggestions to double the rope - we didn't have enough to double through the entire system, and it wouldn't have worked well either - it was hard enough with one rope not to end up with rope-on-rope anywhere. RC0's suggestion (double rope and rig normally) might well have worked - we'd have run out of rope before the ground but we could have taken the hit on our 3-strand and joined it to the dbl-braid after we took wraps on the trees. We'd still have strength loss - 35% is the assumed loss for a clove hitch I believe - I wonder what the strength loss at our shackle ended up being? We broke a (nominally) 50t rope setup so I guess the strength loss must have been > 50%?

[joe into trees]

We broke a (nominally) 50t rope setup so I guess the strength loss must have been > 50%?

 

Unless of course our estimation of peak load is way off. Which it probably is.

 

Also: our reliance on using the elongation of the rope to slow the piece was negatively affected by our setup. 7-8m of elongation before break actually worked out at approx 3m by the time it was doubled and we lost possible elongation due to friction (between the log and the possible-extending section of cordage). Watching the vid, it looks like all of the possible elongation has taken place already by the moment of peak force (when the change in velocity of the snatched timber is highest - right when it broke in fact!).

[Stephen Blair]

Congratulations to Codz Family:thumbup1:

[scotspine1]

Watching the vid, it looks like all of the possible elongation has taken place already by the moment of peak force (when the change in velocity of the snatched timber is highest - right when it broke in fact!).

 

How about adding another Aquatec rope to the setup with the idea that your cradle rigged rope (A) takes the initial impact (or shock load as the timber hits the rigging)

 

then if you leave some slack in rope B so that it takes over when A is nearing max elongation - the velocity subtracted from the falling timber by A may be just enough for rope B to stop the timber

 

Maybe a like for like setup but there would be difficulties with the 2 systems interfering with each other at the branch union.......

 

In general though, when you look at this pic, the forces, angles and the massive amount of friction being created at all sorts of points and distances leaves you with only one conclusion, you need a stronger rope.

Edited February 19, 2013 by scotspine1