Question on the vertical speed line

Gorman

Gorman

Branched out member
Location
Rhode Island
Does the line NEED to be pretensioned in order to work properly? Or can you have it a little slack? The reason I ask is because I used it for the first time with some mega wood earlier in the season (36" ash sections) and I had the speed line break on me. It happened so fast I don't even know for sure why but I was hoping to rule some reasons out. I kept the lengths to about 3 to four feet.
 
Do you know why the line broke? Did the piece rotate on the way to the ground and put a huge dynamic load on the line? When I use vertical speed lines I always pretension the line. Where did the rope break. Were you in the tree when it happened and what do you think happened. What type of rope were you using. It's difficult to know what may have gone wrong, but based on your question, having the load hang up on the way to ground might be a good place to start. Any pics of the job? What were the results of the broken rope? Did it break early, mid or late in the path to the ground? Why did you choose the VSL as the rigging method?
 
Like all rigging questions---it depends.

Do you know where or how the rope broke?
What size/type rope are you using?
Was the chunk attached with a sling?
36"length/diameter? What was the diameter/length?

In most of my VSL setups the groundie kept the rope tight until the chunk hit the ground. Then they might, or might not, let it run a little. It depends...
 
The piece was about 30" in diameter and four feet long.
The rope I was using was a half inch stable braid (an old one)
The piece was attached with a sling with a steel biner

The rope broke about six feet under where I had it choked to the top of the trunk.
My buddy suggested that the rope got caught in between the trunk and the piece and got hammered.

And the line was not pretensioned.
 
[ QUOTE ]
The piece was about 30" in diameter and four feet long.
The rope I was using was a half inch stable braid (an old one)
The piece was attached with a sling with a steel biner

The rope broke about six feet under where I had it choked to the top of the trunk.
My buddy suggested that the rope got caught in between the trunk and the piece and got hammered.

And the line was not pretensioned.

[/ QUOTE ]

This brings up a few more questions. How did you get a 30" piece to leave the spar? Tag line? What type of cut? Was the VSL attached to the base of the tree and how? The 6' below the cut is a clue that your buddie might be right. With wood that big you must have been pretty close to the ground. How old is old? (Obvious anwser...too old)
 
It was a deep deep notch. About half way. Nothing was damaged (aside from the rope) so luckily I got off easy, but still wanted to take a lesson away from it. I just wanted to know if it's necessary to pretension the line to prevent a snag up.
 
Anytime you dump a log of considerable weight onto a VSL you need to make sure that the weight never hits the rope. If it cattches or hits a belly it will load a short singled line hard and fast and pretty much immediately overwhelm the ropes ability to absorb the energy and break.

I think tightening the line reduces this risk but that could be hogwash. I broke a few slings on a VSL when I let the log fall past the ground anchor on a hill. It was like the 1/2" sling wasnt even there.
 
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Gorman, I think what you need to consider going forward is just to reduce the size of the pieces you are sending into that system. Being that it is a guided free-fall more than a controlled fall, there are many factors that can come into play and cause a shock load.

Another option would be to run your normal sling and block in addition to the vertical line and simply use the vertical line as a tag to reduce swing.

You might also try using a beefier line that is not the oldest rope on the floor at the shop. VSLs are typically not extremely long, so purchasing a dedicated piece of "Dynasorb" or similar line may be worthwhile.

Final mention: An X-rigging ring sling or similar hardware would have less tendency to pinch or snag the rope.

Nevermind, just thought of this: running the VSL through an overhead lowering device like Tom uses would give the climber the ability to introduce slack when needed. I might try that actually...
 
[ QUOTE ]
Sooooooo, how do u make sure the line doesn't catch the weight?

[/ QUOTE ]

No Stubs, no slack? I broke a few slings doing VSL, but never before the piece hit the ground, and only when it fell past the ground anchor.
 
Yeah it worked awesome, used a prussic to tention the 3/4 rigging line, made adjusting for height as blocked down a breeze, also meant no expensive mechanical devices in the drop zone to get damaged
 
Simply put, the piece was too big. The tension in the line goes up really high when weight is applied to the speedline. Applying slack to the line wouldn't help. You have to take smaller pieces.

Joe
 
Would it help to offset the notch direction from the vsl so the piece is less likely to hit the vsl at the top? Should have broken at the knot if all else was equal and the log did not hit the rope, but with an old 1/2" rope who knows...
 
With VSL you want to let the ground take the impact and just keep the piece from taking a bad bounce...

I prefer to use a bit of slack in the system, but I honestly couldn't say for sure that it's the way to go, because I haven't used it enough to find out all the things that go wrong.. I did break one rope with a VSL, but I was only trying to keep the but of the 30' top close to the trunk so it didn't fall backwards after landing... so the VSL did the job...

In thinking about the force multipliers in regular speed line, they can get huge when the line is pretensioned..
I'd stay away from it... longer sling and keep the VSL offset to the fall

 
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