how to keep a knot from tightening too much when lifting something

Tractor Seabee · May 10, 2020

ruffdog said:
Some other ways to connect straps:

Joining Two Slings

There again by using those knot types you are drastically reducing the load capacity and compromising the slings integrity. That procedure is not condoned. When you take a rigging course like I have you,learn all this stuff and they have examples of failed straps due to various knotting methods. Large shackles are the only proper answer. When you see pictures of heavy loads dropping due to failed straps it is a wake up call. Conversely for us on TBN not at our full time jobs; we will not be picking loads we have to worry much about either weight or height from the ground. As a construction worker though safety becomes a habit that you do not break, even at home or the farm.

Times when I was assigned as a safety inspector it was not uncommon to find a whole gang box full of straps that had seen better days. It cost more to send them out for load testing than to replace them. When condemned we painted the loops red.

Old Navy Boatswain Mates can tell a lot of sad stories about failed rigging.

Ron

bigtiller · May 10, 2020

downsizingnow48 said:
The running bowline has the anti-tighten quality of the bowline plus it will tighten up on whatever you tie it around.

I use a bowline quite often, especially when the rope will be used for lifting when it is under water. It comes apart easily when wet. But I have never used the running bowline.......

So the squirrel comes out of the hole, between the limbs and back into the hole? Interesting, I'm going to try it today.

ruffdog · May 10, 2020

Tractor Seabee said:
There again by using those knot types you are drastically reducing the load capacity and compromising the slings integrity. That procedure is not condoned. When you take a rigging course like I have you,learn all this stuff and they have examples of failed straps due to various knotting methods. Large shackles are the only proper answer. When you see pictures of heavy loads dropping due to failed straps it is a wake up call. Conversely for us on TBN not at our full time jobs; we will not be picking loads we have to worry much about either weight or height from the ground. As a construction worker though safety becomes a habit that you do not break, even at home or the farm.

Times when I was assigned as a safety inspector it was not uncommon to find a whole gang box full of straps that had seen better days. It cost more to send them out for load testing than to replace them. When condemned we painted the loops red.

Old Navy Boatswain Mates can tell a lot of sad stories about failed rigging.

Ron

Yes, I have taken rigging "courses" and I have worked in machine shops that depended on extensive rigging. The one shop we used straps from 1" wide to monster 16" wide by 1.5" thick. Also, we used about every type of lifting chains out there. We machined parts from a hundred pounds to 120 tons.

If you are using a 4000lb strap to lift 300lbs, I think you are fine on compromising on the knot type being that you are well within the capacity of the strap. Sometimes, a person has to safely improvise.

Captain Dirty · May 10, 2020

Tractor Seabee said:
. . . for us on TBN not at our full time jobs; we will not be picking loads we have to worry much about either weight or height from the ground. As a construction worker though safety becomes a habit that you do not break, even at home or the farm . . .
Ron

Depending upon the type os steel, shackles may have a safety margin of 4X or 6X (Safe Working Load or Working Load Limit or Maximum Securing Load is 1/4 to 1/6 of the Breaking Strength). This allows many (of us) to "get away with" bent, worn, or otherwise unsuitable devices a knowledgable inspector would reject. Be aware that big box stores often market their lifting or lashing materials by breaking strength. A competent rigger automatically de-rates mild steel shackles and rings by half, chain and web lashing by half, (re-used) wire rope and fiber rope by 2/3 (i.e. SWL = 1/3 BS). According to a pamphlet I have from a cordage company the hauling strength of a bowline is 50% of the tensile strength of the rope, a bowline on a bight is 60%. Note this is for round, laid (twisted) rope.