Next generation snatch block

[Vinman]

Isn't that a false positive anecdotal position? You know we also never heard about all the parachute designs that didn't work either.

Pretty sure theres a good reason the failed parachute owners didn’t have much to say after they found out they didn’t work.
On the upside, those parachutes came with a lifetime warranty...

 

[DaveInDenver]

Pretty sure theres a good reason the failed parachute owners didn’t have much to say after they found out they didn’t work.
On the upside, those parachutes came with a lifetime warranty...

Bingo, the failed winch line made one user into two? It's like the mistake of using a trailer ball as a connection. It persists because many people who do that where it fails don't make it to tell others not to.

Or my honest suspicion is that most people don't use their stuff that often and haven't found its limits, if it exists.

 

[MartinDWhite]

...
But can't is a strong word since there's obviously some non-zero amount of friction involve. The rule of thumb threshold to sustain a burn is 70°C (~158°F) and indefinite heat tolerance is 45°C (~110°F). So we're sitting right in the region between comfortable and too hot to handle (being immediate pain) for most people.
...

I will stick by my statement that heat from a winch using a soft shackle and synthetic line over an aluminum pulley block can't hurt either line. There is just not enough energy from the winch to heat the block with friction to a temperature that can damage the line. There is not enough distance in a pull (60 ft max). There is not enough friction. There is just not enough power put into that part of the system to cause the heat level that could do damage.

 

[DaveInDenver]

I will stick by my statement that heat from a winch using a soft shackle and synthetic line over an aluminum pulley block can't hurt either line. There is just not enough energy from the winch to heat the block with friction to a temperature that can damage the line. There is not enough distance in a pull (60 ft max). There is not enough friction. There is just not enough power put into that part of the system to cause the heat level that could do damage.

Based on what do you stand by your statement? References or qualifications? The word of some dudes on the Internet or Youtube doesn't placate the Board who reviews complaints lodged against licensed professional engineers. That's why math and standards exist.

So anyway, back of the napkin calculations using the number from Robert Pepper's video that the ring loses 37 kgf for every 500 kgf would mean for every 1,000 kgf of stuck you move 60 feet the friction ring does I think roughly 6,650 J of work. If you move this length in 600 seconds (just to pick an aggressive number) means that 6,650 joules generated 11 watts of heat.

If those calcs seem about right then, see, that wasn't so hard for you to prove. No taking anyone's word for it.

I'll stand by my preference for rated and testable rigging but that's only an opinion that I guess not many people share anymore. I'd still like to know if Sampson's got testing and one should probrably be concerned about grit in the rigging being ground into the rope and on the surfaces. But that's something you need to always watch.

 

[MartinDWhite]

Based on what do you stand by your statement? References or qualifications? The word of some dudes on the Internet or Youtube doesn't placate the Board who reviews complaints lodged against licensed professional engineers. That's why math and standards exist.

So anyway, back of the napkin calculations using the number from Robert Pepper's video that the ring loses 37 kgf for every 500 kgf would mean for every 1,000 kgf of stuck you move 60 feet the friction ring does I think roughly 6,650 J of work. If you move this length in 600 seconds (just to pick an aggressive number) means that 6,650 joules generated 11 watts of heat.

If those calcs seem about right then, see, that wasn't so hard for you to prove. No taking anyone's word for it.

I'll stand by my preference for rated and testable rigging but that's only an opinion that I guess not many people share anymore. I'd still like to know if Sampson's position and one should be concerned about grit in the rigging being ground into the rope and on the surfaces. But that's something you need to always watch.

To continue with the math (and arguing uselessly on the internet with a total stranger) it takes over 9,000 joules of heat to raise the temp of the 600 gram aluminum block from 90*F to 150*F ( Q = m x c x ΔT ). That means the 6650 J of loss in the system, if completely converted to heat, is not enough energy to get to the required temperature to do damage? AND that assumes there is no heat loss from radiant heat, and no heat goes into the rope.

I have sent several rings for pull testing on a certified pull testing rig. I have had tests done with temperature guns during pulls. I have a degree in engineering (computer engineering, so only slightly related, but I slept at a holiday inn express last night).

 

[Metcalf]

The knot is the weak point and will break in all 1/2" soft shackles at less than 40,000 lbs. specifically the rope on entry to the knot will break if the knot does not slip undone. I know this because it is the failure mode for every block I have tested.

I'm curious, what style soft shackle are you testing where the knot is failing?

 

[Vinman]

Never mind all the engineering tests, how many people are having soft shackle failures in the real world of winch recovery? Sure, they may fail before a steel shackle but if they do the recovery job without failing, is it really relevant?

Thats like saying all winch plates should be made from 1/2” thick steel because it’s been proven 1/2” steel is stronger than 1/4” steel.

 

[MartinDWhite]

I'm curious, what style soft shackle are you testing where the knot is failing?

The style with one rope completely inside the other rope. I have not tested the split rope design.
Knots are the failure point in just about any rope setup unless there is undo rope wear. That or the rope over an edge.

Are you testing some soft shackles that are not failing at the knot?

 

[Metcalf]

The style with one rope completely inside the other rope. I have not tested the split rope design.
Knots are the failure point in just about any rope setup unless there is undo rope wear. That or the rope over an edge.

Are you testing some soft shackles that are not failing at the knot?

Getting the knot as tight as practical really seems to help. I think this pretty much needs to be done in fixture to properly set the knot inline, not unevenly at an angle. It does add some expense. I do think that it happens pretty naturally over time as long as your not going to MBS in the first pull.

All my stuff is the 'improved' style with the double legs AND the legs fed back down. This gives more cross sectional area to help increase the minimum bend radius at the noose.

Most failures in this style of shackle seem to be in the noose. I think this comes more from the 'sawing' action of the noose tightening on the neck than anything. The knot is no longer folding off as long as it has been tightened.

The more formal testing at Factor 55 seems to correlate with this.