ratchet strap failure, whilst rigging

[Marc]

However the capstan is attached to the tree, and however much slack there is in the attachment software, you should still be able to pretension the lowering rope. Much easier with two groundies, but even if you have to pull down on the rope with one hand and make the first wrap with the other you should still be able to get it fairly tight?

 

I'm talking about snatching only mate as the piece goes over, any other rigging situation its easy to keep tension in the rigging line.

[Peter]

Haha, serious thread overlap going on here, I'v just replied to that in the other thread!

[carlos]

hi glad you are ok sam.

would be interesting to get bit more info, floatin capstan or bollard?. most ratchets i have had were rated at 5ton( think thats safe working). but when holding down a load they would have little or no shock loading (iam asuming its not an intergral one on a hobbs or similar) also if they had been used to secure logs on a truck for a year or two the rating would have gone out the window( not impliying that was the case with you )but would be worth having seperate ones for each task. i know our one get used for allsorts ( not rigging after this thread) carl

[Peter]

most ratchets i have had were rated at 5ton( think thats safe working).

 

That is a very dangerous assumption to make.

 

Assuming it is SWL, the breaking strain at a safety factor of ten must be 50 tonnes. Even snatching a 250 kg lump is very unlikely to generate that force.

 

If it is breaking strain 5 tonnes, then a SWL at a SF of ten brings it down to 500kg. Suddenly your 250 kg snatched lump generates enough Kn to destroy the cycles to failure, and you have an accident waiting to happen.

 

If you are going to use kit to handle big loads, you must know what it is capable of. Assumptions will cause accidents.

[treequip]

I am going to assume that the strap was girthed around the tree with a friction device secure to it.

 

The main weakness I can see is that the strap is designed to be loaded in a linear manner. Notch loading a point on the strap is going to compromise the system. The ratchet tensioned is also going to be a weak point particularly in the shock loading scenario.

 

Andy

[carlos]

hi peter.

dont worry iam not about to drop 1/4 ton bit of wood onto a piece of gear with out checking wether the rating is breaking or working limit, i usally only use them for load tying applications.will check and post a definate " working load" to clarfiy my assumption. carl

[sam walton]

bloody hell! I was working all yesterday and all today, just turned on my computer with 26 replies to read. I cant reply to all but.. the strap had no twists, was in reletivly good condition, rated to 5 tonne and the drop was as minimal as you can get it. however it was the first time we had used it so we was still in the experimental stages of how many wrapps needed ect and thats why there was no run to fiz out the shock. Im not sure what type of kapstan it is, whether floating or bollard and im gonna sound like a right cowboy here but i made myself, coppied it off a picture i had seen on ebay. we cant all afford hobbs! anyway thanks for you guys who showed a bit of consern but i really am fine. what are your thoughts on a chain ratchet?

[Peter]

Any chance of a pic? Sounds interesting!

 

I had a look at one of my 5 tonne ratchet straps today, the 5 tonnes is MBS, the SWL as a load tie down is 2.5 tonnes, but in a rigging situation you should apply a greater safety factor.

In short, it wont be up to the job, but you already know that!

 

Chain ratchet could work, but why not use the right tool for the job and get a sling?

[sam walton]

haha, yeah i found out the scary way. i dont reckon you can get a sling tight enough to stop the kapstan sliding up the tree. I'l try get some pictures of the snapped strap and the kapstan i used. I think the eges of it could be too sharp and may needed a little more grinding or sanding.

[Mr Ed]

Or use 3 ratchet straps. Any type of twisting or shear force on the webbing will snap them, so having more than one to hold your bollard straight will help immensly. I have a few truck straps that are 10t mbs. 3 of them on your bollard should work well...