Staying within the SWL of your rigging

[emr]

Does anyone actually figure out the weight of what they are rigging to stay within the safe working load limits of their gear? If so, what SWL factor are you using?

We never used to worry about it too much because we never really took big enough pieces to get close but after getting the GRCS we have been taking bigger pieces. I do rough calculations when taking bigger prices which is usually when we are wincing up on wood. That also brings up another question, will you push the limits when lifting vs lowering? My thought is that you could use a 5:1 safety factor when lifting because there is no shock loading and a 10:1 safety factors while lowering because there will be shocked loading.

 

[Burnham]

Not a bad rule of thumb, Eric. Either way though, always keep cycles to failure in mind...if you keep loads well under SWL limit for the weakest link (which should be the rope, I'm sure we all agree) you extend the number of safe cycles.

 

[Burnham]

Another thing to remember is to calculate the loads when negative blocking bearing in mind the exponential increase as distance from the block to the COG of the piece gets longer.

 

[emr]

Since we have been advancing our rigging techniques we have been doing lots of research and getting additional training in the new to us techniques. There is all sorts of talk about rope angles and calculating forces and I was wondering if people out there are doing the math or just figuring they are taking small enough pieces. Like I said before we always just figured that we were taking small enough pieces. Things like distance the piece falls during negative blocking and rope angles and such have always been in the back of my mind, but now they seem to be more important.

 

[Burnham]

For myself, I've looked up on the log weight charts some basic general size/weight categories I keep in my mind, for the species I commonly work with. I interpolate from there.

 

[pete mctree]

Good clear thinking & posting

I have little to add at the moment other that slings (inc loopies dead eyes etc)usually have a safety factor of 7 to 1 thus retaining good cycles to failure.
Textiles are always difficult to access with regards to loading & abuse especially when you are not on every job.

Good thread

 

[PCTREE]

When I first started using our GRCS we had a hackberry to take down that was loaded with ivy. There was a 10" lead that went out over the house and power lines. I decided to tip tie and winch it up with the GRCS as parting it out would have been a pain due to ivy. Anyways the block was set on 5" wood at top of tree that was vertical. I started undercutting and groundy started winching, lead didn't raise as expected, I looked up and the top was bent WAY over. Scared the heck outa me, I swung out and started cutting small pieces off to reduce weight before the top broke out. All ended up OK but I haven't been winching any more big leads with the GRCS. Obviously I underestimated the weight of the ivy.

I have worked 24 years taking regular sized pieces and have never had a rigging failure, only once had a top in a very dead tree break out. When you start thinking about needing to calculate SWL IMO maybe you should just make 2 cuts. Remember cycles to failure of your gear is dependent on the % of the rated weight, something like if you load a rope to 95% its tensile strength you can only cycle it about 10 times before it breaks, load it to 10% and you can cycle it thousands of times. For me I would rather take smaller pieces and not have to worry about stuff breaking.....

 

[pete mctree]

It would be a good idea to get used to installing multiple blocks if you don't already, especially when rigging on condom stems. A lot more strength when you can compress the union

 

[PCTREE]

As paranoid as I am I will always distribute the load as much as possible and try to keep the wood under compression.....

 

[pete mctree]

Not paranoia Paul, just good sense

 

[Burnham]

 

[stehansen]

Good job Paul. That is good advice for all of us. Don't be afraid to go to a plan B if plan A isn't working.

 

[Fiddler]

Great thread!

Having just purchased a GRCS I have had the same thoughts contained here.

 

[Burnham]

Here's a link to a thread where we explored some of these ideas. Might be worth a perusal.

https://www.masterblasterhome.com/showthread.php?12254-How-big-can-you-go

 

[treesmith]

Another thing to consider is the angle of of the limb you're winching, Paul. A near-horizontal limb will require more "lift" than a limb that is already at 45* and merely needs "standing up". We used the GRCS on a job a few weeks ago, where I notched and backcut a big limb, then swung away so my groundie could winch it up. He winched til the HoleHawg couldn't pull anymore then stopped. I had to swing out and cut a little more so he could finish winching it around. In a more ideal situation, we would have been lifting more. As it was, we were pulling more horizontally, with not near enough lift.

As to rigging point integrity, I had to rope out a piece this morning that prolly went 300#, which normally isn't much, but considering the condition of the tree (see Work Pics thread), it was way more than I wanted to rig. Had to though, because it was hanging out over the primary. I threw a line up into a fork, routing it through another fork, and took a couple of redirects around two stubs. Less restriction than a wrap, but would enable my groundie to control it. I told him to hold it til it cleared the lines and just let it go. It sailed down, pretty as you please, with little shock-loading to the tree, which I was thankful for, as I was riding it out.

 

[Tucker943]

I don't calculate at all when roping. I use my judgement based on experience, the species, the tree itself, and the gear I'm using. I suppose I do calculate, but not with numbers.

 

[woodworkingboy]

For fun, I look at a lot of Pines with lean and different limb configurations, and ask myself if the tree could be pulled opposite the lean and fallen successfully. Some trees are at the "don't know" point and it would likely be better not to try in a critical situation, and how I know that point is that I get a little cringe in my stomach, remembering a bad experience.

 

[Tucker943]

I remember the experience you speak of Jay. Atleast I think I do? The tree that refused to get moving?

 

[woodworkingboy]

Ya Chris, that's the one.

 

[tophopper]

I don't calculate at all when roping. I use my judgement based on experience, the species, the tree itself, and the gear I'm using. I suppose I do calculate, but not with numbers.

+1



The only time I generally get out my green weight log chart is on a crane job.

 

[JoshINtrees]

When I'm in doubt, I try to err on the far side of caution.