HOw much do various knots weaken a line

[Gary Fox]

"It is a good argument to have a spliced loop instead on a mooring line."

NO! If you reckon that the breaking strain of a mooring line is at least ten times greater than the load that will be applied to it, unless of course you moor using string!

I've snapped quite a few mooring lines over the years, due to swell, ships' wash etc, and I use thick ones.

 

[Wing Mark]

I've snapped quite a few mooring lines over the years, due to swell, ships' wash etc, and I use thick ones.

Does it occur to you, there might be a better technique which doesn't break lines?
Or if the line had not broken, would something else have broken instead?

 

[newtothis]

I read that a bowline reduces the breaking strain of a line by 40%. It is a good arguement to have a spliced loop instead on a mooring line.
I wonder if someone has tested lots of different knots and their effect on breaking strain?

TudorSailor

PBO of this stable did a workshop test on different knots/splices etc in recent history (last 10 years, anyway). They had big measuring machines that could put tonnes of pressure on a rope and record at what point it failed.
I don't have a copy any longer, but you may be able to delve around in the archives.

 

[sarabande]

Does it occur to you, there might be a better technique which doesn't break lines?
Or if the line had not broken, would something else have broken instead?

I suspect that you know little about the forces in commercial towing and mooring, otherwise you would not have made that post.

 

[Kukri]

I am interested (and I may not be the only one) in the strength of a halyard knot tied in Dyneema.

 

[Gary Fox]

I am interested (and I may not be the only one) in the strength of a halyard knot tied in Dyneema.

Yes me too, and whether it would pull through itself, using that slippery stuff. But that knot seems promising, as does a fisherman's bend, due to the way it grips itself.

 

[dunedin]

Yes me too, and whether it would pull through itself, using that slippery stuff. But that knot seems promising, as does a fisherman's bend, due to the way it grips itself.

The halyard knot won’t slip in typical cruising dyneema, if tensioned properly - we winch it tight between two winches to fix it when new.

But with proper race dyneema it would be madness to do anything other than a proper dyneema splice

 

[zoidberg]

There are lots of 'experts' to answer that question - some of them with YouTube channels and who write articles for sundry editors here and there.
I've had reason to research many of the confident sources and, like much else in t'internet world, it all depends on who you ask.

For my specific purposes, I asked Paul Dyer of Marlow Ropes. Several other industry pros agreed 'chapter and verse'.

They'll also tell you that the detail of how a knot is tied or a loop spliced, and the conditions in which it is used, have significant influence on performance. For example, the bend radius or 'D:d Ratio' impacts the MBL of a spliced loop in most ropes. Tight bends overload 'outside' fibres which causes sudden 'progressive' failure. That's why bollards are big fat lumps and not big slim lumps.

The length and style of the 'bury' in single-braid Dyneema matters a lot. So does the skill of the splicer.

Wet nylon rope is not nearly as strong as dry nylon; it degrades or 'fatigues' under cyclic loads far faster than other ropes.

Climbers retire their climbing ropes after a number of falls before the rope retires the climber.

There will be some who will come on and disagree loudly. That's the price we pay for internet. I'm just the messenger....

 

[mucklestone]

I have enjoyed reading this thread.

I find this a really interesting topic, but can't help think it has little practical application. As others have hinted, a rope should be over specced to the point that this is academic. Both knots and splices have their applications.

Personally I would be prepared to bet that 9 times out of 10 when a rope breaks it is age or wear to blame, not ropes being overloaded.

 

[James_Calvert]

............ Personally I would be prepared to bet that 9 times out of 10 when a rope breaks it is age or wear to blame, not ropes being overloaded.

I had a rope break when overloaded.

My son's Topper's mainsheet.

Towing my broken down Volvo estate off a roundabout.

Curiously it didn't break at a knot!

 

[Wing Mark]

I have enjoyed reading this thread.

I find this a really interesting topic, but can't help think it has little practical application. As others have hinted, a rope should be over specced to the point that this is academic. Both knots and splices have their applications.

Personally I would be prepared to bet that 9 times out of 10 when a rope breaks it is age or wear to blame, not ropes being overloaded.

I think you are right.
The other thing is, if a rope is highly loaded, it will be stretching and relaxing every time the load fluctuates.
Say you've gone for a nice, low stretch halyard, and loaded it to 20% of breaking. It will stretch about 2mm per metre. Every time you go over a wave or get a gust, that load will vary, so the rope moves a few mm.
So the lab tests are very interesting, but not much like real life on a boat. On dinghies, we use thin dyneema for quite a lot of things, the highly loaded bits need changing every year or so, and we only race a few hours a week.
There's a knot at the top of my dinghy mast, I shorten the halyard by a cm or two every time I take down the mast, other wise the halyard will eventually fail at the knot. Obviously it moves all the other wear points too.

The other question is, what fraction of the rope's breaking load can a cleat or clutch hold? Of course on dinghies, we often cheat by 'tapering ropes, the bit in the cleat might be 6mm. the working part might just be 3 or 4mm of dyneema 'core'. Again, if you push the limits, it wears both the cleat and the rope.

 

[Wing Mark]

I had a rope break when overloaded.

My son's Topper's mainsheet.

Towing my broken down Volvo estate off a roundabout.

Curiously it didn't break at a knot!

I broke a dinghy mainsheet with my own bare hands!
It was a dinghy with a mainsheet 'hoop' and the cover exposed a section of the sheet to sunlight for a few years.
Maybe the bit that broke was where your son held the sheet in his teeth?

 

[Wing Mark]

How do people estimate what the load on e.g. a main halyard really is?

 

[Daydream believer]

Towing my broken down Volvo estate off a roundabout.

Drunk was we?

 

[Kukri]

How do people estimate what the load on e.g. a main halyard really is?

Second that question! ?

The halyards on my boat terminate in halyard knots. They are probably the only lines that come under anything like a load that approaches their breaking strain.

But what is it?

 

[Yealm]

Yes me too, and whether it would pull through itself, using that slippery stuff. But that knot seems promising, as does a fisherman's bend, due to the way it grips itself.

.

 

[Yealm]

I am interested (and I may not be the only one) in the strength of a halyard knot tied in Dyneema.

I use a lot of dyneema soft shackles - they're great, never had problems. I think common on racing boats. But I guess spliced, so irrelevant to your question

 

[andsarkit]

The Estar Hitch was developed by Evans Starzinger specifically for dyneema halyards. He did write up his extensive testing of various knots but I don't think it is still available since he closed his website.
Found some information here: Knot testing

 

[Kukri]

I use a lot of dyneema soft shackles - they're great, never had problems. I think common on racing boats. But I guess spliced, so irrelevant to your question

So do I. But I think the point of failure on a soft shackle is the button knot, afaik?

Edited: just read quickly through the postings by Evans Starzinger that andsarkit posted a link to, and yes, the soft shackle fails at the button/diamond knot.

 

[sarabande]

Some data on halyard and sheet loads here.

Calculating Halyard Loads — Rigging Doctor