Dyneema rope suitability

Who are you using to supply the rope? If there is a local fishing fleet whoever supplies the trawlers will have much better practical experience of what you are trying to do than anyone else locally is likely to and I wouldn't be surprised if there isn't a specialist version of dyneema specifically for the trawlers now which would probably suit your application better than the marine versions that we all use, I think they used to use dynex dux, but I imagine that they should have come up with something even more specific by now.
 
As a climber I am advised never to use dyneema from sole connection to primary anchor as it snaps under excess shock load as incapable of streching. Several deaths have occurred from climbers falling a mere two metres from belay achors when attached solely with dyneema.

It is safe to use for climbers if via a long enough intermediate connection of stretchy material, as that then absorbs the shock. For climbers this means attaching via another sling or onto the primary climbing rope, not directly to the safety harness.

It seems unsuitable for the OPs intended usage
 
oldmanofthehills said:
As a climber I am advised never to use dyneema from sole connection to primary anchor as it snaps under excess shock load as incapable of streching.

It seems unsuitable for the OPs intended usage
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As mentioned upthread you specifically do not want a stretchy cable in scenarios like this because a stretched cable has considerable stored energy (which is exactly what makes a dynamic rope good for climbing) which will be released when the cable snaps with potentially lethal consequences.

Shock loads are avoided by doing everything slowly, and never allowing any slack to build up. What you cannot avoid are load multipliers from e.g. pulling the sinker out of the mud.
 
The talk about shock loading pulling the sinker out of the mud is, I suspect, a red herring: the winch is mounted on a work-boat, and a sudden 16 tonnes of load will pull the boat down in the water a bit which provides some protection. And 16 tonnes is a lot of excess snatch load on a 1 tonne sinker. Besides, the line will never break in the middle but always at a splice or knot unless damaged at the point it breaks.

So I very much suspect that the line is breaking due to a defect in the line such as a kink, and a sudden peak load (as very cogently suggested earlier) by a jam in the passage of the mooring assembly over the roller of the work boat.

As mitigation I would fit a strain gauge on the winch if it doesn't have one, and probably, the winch being hydraulic, an auto-release on excess loading. Breakages should never happen, and each one needs root-cause analysis and lessons learned to be put into the operating procedure and/or design.
 
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coveman said:
Except the OP states the line broke 4 to 6 ft back in #39
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I noticed that, which is why I made the comment about a rope never breaking in the middle unless somehow damaged there, which is why I went on to say "So I very much suspect that the line is breaking due to a defect in the line such as a kink"
 
st599 said:
Doesn't tying a knot in Dyneema reduce its working load by 60+%?...
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Yes, that's exactly why it's normal that a line breaks at a knot not along its length. So the breakage occurring not at an end but somewhere in the middle should be a clue as to cause.
 
jdc said:
I noticed that, which is why I made the comment about a rope never breaking in the middle unless somehow damaged there, which is why I went on to say "So I very much suspect that the line is breaking due to a defect in the line such as a kink"
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Sorry, I missed that, but in his initial post he states that this has occurred four times which would indicate to me that there is something fundamentally wrong with the system being employed or a faulty batch of rope.
 
oldmanofthehills said:
As a climber I am advised never to use dyneema from sole connection to primary anchor as it snaps under excess shock load as incapable of streching. Several deaths have occurred from climbers falling a mere two metres from belay achors when attached solely with dyneema.

It is safe to use for climbers if via a long enough intermediate connection of stretchy material, as that then absorbs the shock. For climbers this means attaching via another sling or onto the primary climbing rope, not directly to the safety harness.

It seems unsuitable for the OPs intended usage
Click to expand...
I am not sure whether the concern in that situation is the snapping of the dyneema rope - the safety factors normally would make that very unlikely. However, snapping the climber is a very real concern, which is why you would like a more stretchy rope in the system to give the climber a softer arrest at the end of their fall. This also will reduce the peak load on the anchor, which is also likely to be a real concern.
 
rgarside said:
I am not sure whether the concern in that situation is the snapping of the dyneema rope - the safety factors normally would make that very unlikely. However, snapping the climber is a very real concern, which is why you would like a more stretchy rope in the system to give the climber a softer arrest at the end of their fall. This also will reduce the peak load on the anchor, which is also likely to be a real concern.
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The poster is correct. The Dyneema slings themselves broke in the cases he is citing. The climber almost certainly felt the pain too, but since he also hit the ground....
 
rgarside said:
I am not sure whether the concern in that situation is the snapping of the dyneema rope - the safety factors normally would make that very unlikely. However, snapping the climber is a very real concern, which is why you would like a more stretchy rope in the system to give the climber a softer arrest at the end of their fall. This also will reduce the peak load on the anchor, which is also likely to be a real concern.
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As a designer engineer controlling risk we are now instructed that unreliability is itself always a safety risk factor, and that better reliability may be preferable to absolute safety of failed mode, due to loss of control at that failure point.

Strectchy rope is clearly no good for the OPs usage. However dyneema though apparent failing in a non-whippy mode, presents out of order events at point of failure thus creating its own risk. Unless the dyneema is increased in capacity and the winch amended to reduce the strain, it seems that suitable steel rope might create less hazard
 
TLouth7 said:
This is an incredibly bad idea. The entire appeal of using dyneema is that it is not stretchy, so there is minimal elastic potential energy to be released when the line snaps.
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But established practice is to use steel, which doesn't break in the first place. Winching horizontally on land with dyneema is a very different application.
On the sea, you need some give in the system I think.
It's similar to using a length of kevlar to tow a boat, I've seen people break very strong things like that.
 
jdc said:
The talk about shock loading pulling the sinker out of the mud is, I suspect, a red herring: the winch is mounted on a work-boat, and a sudden 16 tonnes of load will pull the boat down in the water a bit which provides some protection. ...
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That is entirely flawed.
A sudden 16 tons won't move the barge instantly, the mass of the barge and the mass of the water surrounding it allows very high instantaneous loads to occur.

Dyneemahas something like 1% stretch to break? So for every metre of water depth, a centimetre of wave height would be enough to break the dyneema.
 
oldmanofthehills said:
As a designer engineer controlling risk we are now instructed that unreliability is itself always a safety risk factor, and that better reliability may be preferable to absolute safety of failed mode, due to loss of control at that failure point.

Strectchy rope is clearly no good for the OPs usage. However dyneema though apparent failing in a non-whippy mode, presents out of order events at point of failure thus creating its own risk. Unless the dyneema is increased in capacity and the winch amended to reduce the strain, it seems that suitable steel rope might create less hazard
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Translation to English - anybody?
 
TernVI said:
It's similar to using a length of kevlar to tow a boat, I've seen people break very strong things like that.
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It isn't really very similar. A tow rope is over the water, out of the way of people. I'm sure it is standard practice to keep clear of the tow rope where it is attached to each vessel. Snatch loads are also unavoidable if you want to tow at any reasonable speed; even so drogues are sometimes used to prevent buildup of slack. In contrast there is no reason for snatch loads when lifting a sinker.
 
We don't have a bow roller, we have a chute that is angled to let the chain slide in. Lifting the sinker with the riser 12mm or 16mm chain doesn't present a problem It flows in smoothly and there is no snatch. The extra strain on both rope and wire occurs when the ground chain is hauled into the chute. Ground chain can be up to 40mm the huge links make it very jerky. Fortunately we only drag about 3/4 feet of the ground chain into the boat to inspect the reeving on the egg link on the riser.
When pulling the ground chain over the chute there is no reason to have more than 4 feet of wire or rope off the drum.

I think Oldmanofthehills is saying, as we have had 15 years trouble free using wire, and 2 months of trials with dyneema which cause have caused concern, why change?
 
TernVI said:
That is entirely flawed....
Dyneemahas something like 1% stretch to break? So for every metre of water depth, a centimetre of wave height would be enough to break the dyneema.
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That is entirely flawed. For 1cm of wave height to have the mass sufficient to exert 16 tonnes of force on a barge the area of the barge has to be such that 1cm x A = 16 cubic metres. This is 1600 m2. A barge of 10m beam and 160m length? I don't think so!
 
jdc said:
That is entirely flawed. For 1cm of wave height to have the mass sufficient to exert 16 tonnes of force on a barge the area of the barge has to be such that 1cm x A = 16 cubic metres. This is 1600 m2. A barge of 10m beam and 160m length? I don't think so!
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Inertia dear boy.

The reality is the rope breaks.
I suggest you go away and understand that fact.
 
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