Dyneema rope suitability

[KREW2]

At our sailing club we have a team of about 10 who drive and operate a 38ft harbour launch that we use to lift and inspect moorings.
Lifting is done with a hydraulic winch which has a 16 ton wire cable. As the ground chain is pulled up over a chute on the bow with a maybe 500 to a 1000 kilo sinker there is considerable strain on the wire.
Some of the team, rightly, have concerns that should the wire part the whip back could cause sever injury to the winch operator. we have been doing this for 14 years and as of yet it has never failed.
Last January we decided to replace the wire with dyneema. In the three months to March we had at least four breaks, I was driving when 2 of them occurred. Now we have a debate among drivers as to the best way forward, wire or continue with the dyneema.
Those pro dyneema say the breaks were safe with no whipping back. Those pro wire say, when lifting weights of 1000+ kilos no break can be considered safe.
The pro dyneemas, some of who are committee members who do not operate the moorings boat, say it should not break because it also has a 16 ton breaking strain.
The argument from those pro wire is that, dyneema may have a good breaking strain but cannot cope with the shock loads that are put on it hauling huge weights and chain from the sea bed.
To me the solution is to move the winch handle so the operator can work from inside the front cabin, protected by the forward bulk head, but that seams too easy for some.

 

[Rappey]

From off roading and winching experience , wire is not allowed on play and pay sites for obvious reasons.
Many winches are 6000kg pull and if the dyneema does snap is usually just falls on the ground without any vicious recoil .
Mooring chains are abrasive and would have thought dyneema would get chafed through too often to make it viable as it's not cheap.
Myth busters used a pig carcass and tried slicing it in half with a wire cable snapping.
The best that they achieved was the carcass getting a slap from the cable.
Can the cable run on the boat deck not have strong steel hoops over it so it couldn't go anywhere if it did snap ?

 

[KREW2]

Can the cable run on the boat deck not have strong steel hoops over it so it couldn't go anywhere if it did snap ?

Good thought but couldn't be done. the winch is about 4/5meters back from the chute on the bow. The riser is pulled onto the fore deck, a chain hook attached and it is hauled in. It usually takes about 4 bites before we get the ground chain on board. When on board bar is inserted through one of the ground chain links, a foot of cable is let out leaving the bar to retain it with the sinker dangling below the bow. I'm always happy when the weight is taken off the rope or wire.

The dyneema does not touch the chain it has a spliced loop at the end to which is attached a chain hook.
In theory it should be strong enough to haul in 1000kg without breaking. It has been suggested that breakages could be caused by grit and bits of broken mussel shells getting into contact with the dyneema.
There is now talk of sheathing the dyneema, but that ain't gonna work the winch guides will just peel it back.

 

[alahol2]

At our club we have a manual winch with a dyneema cable on the mooring barge. We operate in much the same way, taking bite after bite. I'm fairly sure we have had no breaks and we are lifting what must be close to a 1000kg at times. I'm not a regular operator, only occasional.
Maybe, because it is manually operated, we can tell when the cable/mooring jams and give it time to sort itself or let out and try again?
Does your cable part at the same place every time or is it just random?

 

[thinwater]

Where is it breaking? Are there burs remaining from when it was wire? That is the most common problem with wire/Dyneema conversions. It does not take much to cut it when under great tension.

 

[penberth3]

Potential here for a fatal accident. You need professional advice from a lifting gear specialist, not random answers from an internet forum.

 

[rgarside]

Difficult to comment without more information on the lifting arrangements and the nature of the breaks. What size and construction of wire? What size and type of Dyneema? Is the cable subject to chafe? Where did the breaks occur? etc.

I assume you are referring to 16 tonne MBL cable - in 6x36 s/s wire this would be at least 18mm in diameter. The same MBL in Dyneema would be at least 12mm in diameter. One would expect a dyneema line of that size to stretch slightly more than that wire rope. In the event of a break, the dyneema would behave in a more benign fashion than the wire.

 

[jwfrary]

Potential here for a fatal accident. You need professional advice from a lifting gear specialist, not random answers from an internet forum.

this arrangement should be inspected and certified under LOLER regs. Your on seriously dodgy grounds with respect to HSE.

wire or rope it shouldn’t be breaking. And if it’s happening more than once you have either a fundamental problem with the process or equipment or both!

 

[KREW2]

Difficult to comment without more information on the lifting arrangements and the nature of the breaks. What size and construction of wire? What size and type of Dyneema? Is the cable subject to chafe? Where did the breaks occur? etc.

I assume you are referring to 16 tonne MBL cable - in 6x36 s/s wire this would be at least 18mm in diameter. The same MBL in Dyneema would be at least 12mm in diameter. One would expect a dyneema line of that size to stretch slightly more than that wire rope. In the event of a break, the dyneema would behave in a more benign fashion than the wire.

Our wire isn't stainless, it's galvanised I think.

In fifteen years we have never had a break with the wire cable, we have had four with dyneema in two months, but as you say benign it just flopped on the deck.
The breaks that I saw all happened about two feet back from the hook, and I believe the ones that I didn't see were the same.
The only friction on the rope is when it goes through the guide rollers on the winch.
We now have two retaining hooks to hold the chain inboard while taking a fresh bite, one shackled to the winch, and one on a samson post at the bow With the dyneema I reposition the retaining hook after every two feet of bite, which limits the drop if the rope parts.

 

[KREW2]

Does your cable part at the same place every time or is it just random?

In fifteen years of checking moorings we have never had a cable part, but we have with the dyneema. One driver thinks it maybe isn't suitable for shock loads
As has been said by other posters it just flopped on the deck, so no danger of any whipping back.
Just annoying that we have to abandon work for the day and renew expensive rope.

 

[penberth3]

In fifteen years of checking moorings we have never had a cable part, but we have with the dyneema. One driver thinks it maybe isn't suitable for shock loads
As has been said by other posters it just flopped on the deck, so no danger of any whipping back.
Just annoying that we have to abandon work for the day and renew expensive rope.

I'll repeat, get professional advice "thinking maybe" isn't good enough. Why did you choose Dyneema?

 

[alahol2]

The breaks that I saw all happened about two feet back from the hook, and I believe the ones that I didn't see were the same.

I would be looking at the way the eye splice is made, perhaps it's not being tapered enough or long enough?

 

[penberth3]

I would be looking at the way the eye splice is made, perhaps it's not being tapered enough or long enough?

FFS! For the third time - the OP needs to get professional advice.

 

[thinwater]

^^ This. An on-site professional could likely see the fault in moments. Cheaper than breaking something expensive and much better than getting someone hurt. Not worth the learning curve of trying to figure it out at this point. I would have made changes after the first break! No failure in lifting equipment is acceptable.

 

[fredrussell]

FFS! For the third time - the OP needs to get professional advice.

Agreed on the professional advice - but we can still discuss it. This is a forum, it’s what we do.

 

[TernVI]

this arrangement should be inspected and certified under LOLER regs. Your on seriously dodgy grounds with respect to HSE.

wire or rope it shouldn’t be breaking. And if it’s happening more than once you have either a fundamental problem with the process or equipment or both!

I'd say they were a very long way into the bad lands beyond 'dodgy'.

Dyneema's lack of elasticity means the instantaneous loads can be much higher than people might think.
Pulling a 1T sinker out of mud often requires much more than a 1T pull. Even then it comes out slowly, the mud is viscous.
Trying to jerk it out just breaks things.
When the winch pulls the lifting line very close to vertical, a small sidewise force on the boat puts an incredibly large tension on the line.

I think you actually want a slightly springy lifting line, to put a steady, controlled force on it, which doesn't go off the scale if the barge moves a few inches.

Dyneema bent round any curve is quite weak, due to the low stretch, the tension all goes on the oustide of the bend.
Rope under tension is easily cut by anything that not mirror smooth.
Any dirt can cut the rope from the inside.
Any disturbance of the lay of the rope can weaken it grossly.

Do you ever see dyneema on cranes?


As others have said, professional help required.

 

[alahol2]

FFS! For the third time - the OP needs to get professional advice.

 

[penberth3]

Agreed on the professional advice - but we can still discuss it. This is a forum, it’s what we do.

Wrong. This is safety critical, what if somebody follows advice that is dangerously wrong?

 

[coveman]

[QUOTEthis arrangement should be inspected and certified under LOLER regs. Your on seriously dodgy grounds with respect to HSE.QUOTE]

I agree - Inspection,Certification and operator training!
The loads are likely higher than you imagine - pulling the sinker out of mud (suction)is a much higher load than merely lifting the weight vertically and the same applies to the angle of pull. The consequences of a galvanised wire breaking or shackles attached to it breaking would have dire consequences for anyone in close proximity to the wire as it whips back. That is the reason why on a timber winch (which I regularly use) the operator either stands well over 10 metres away from the winch and operates it via a remote rope or if you can afford it an electrical remote system is employed.
The days of "that will probably do it ok" are gone. Not only is it putting someone at great risk but do not underestimate the powers of the Health and Safety Executive, - its just not worth the chance.

 

[RJJ]

Wrong. This is safety critical, what if somebody follows advice that is dangerously wrong?

I'd be quite interested to hear the solution.